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• E/R Diagram Assignment Solutions: Practical Exercises and Techniques

Solving Complex E/R Diagram Assignments: Practical Exercises and Techniques

In the realm of database design, mastering the art of creating effective Entity-Relationship (E/R) diagrams is essential. These diagrams not only serve as blueprints for database structures but also ensure that data relationships are accurately represented. E/R diagrams are fundamental tools in both academic and professional settings, providing a visual framework to model entities, attributes, and the interactions between them. For students, proficiency in designing E/R diagrams is crucial for succeeding in E/R diagram assignment help and comprehending more complex topics in database management.

Throughout this comprehensive guide, we'll explore a series of exercises designed to enhance your skills in designing E/R diagrams for various scenarios. By engaging with these exercises, you'll gain practical experience in structuring databases to meet specific requirements, such as accommodating diverse data types and defining intricate relationships between entities. This hands-on approach is invaluable for anyone studying Database Homework Help or preparing for real-world database design challenges.

By the end of this blog, you'll not only understand the theoretical underpinnings of database design but also possess the practical skills to tackle E/R diagram Assignment Help and confidently navigate complex database design tasks. Whether you're designing a database for a university registrar system, modeling relationships between different types of people, or decomposing intricate data dependencies, these exercises will equip you with the expertise needed to excel in database design. Understanding how to create well-structured E/R diagrams ensures that your databases are efficient, scalable, and optimized for data management and retrieval.

Understanding Entity-Relationship (E/R) Diagrams

Before delving into the exercises, let's first establish a clear understanding of what E/R diagrams are and their significance in database design.

What is an E/R Diagram?

An E/R diagram is a visual representation that depicts entities (things about which data is stored) and the relationships between them in a database. It uses various symbols and connectors to illustrate how entities are related and how they interact with each other.

Components of an E/R Diagram:

• Entities: Represented by rectangles, entities are the objects or concepts about which data is stored in the database. Each entity typically corresponds to a table in the database.
• Attributes: Attributes describe the properties or characteristics of entities. They are depicted within ovals connected to their respective entities.
• Relationships: Relationships represent associations or connections between entities. They are shown as lines connecting two or more entities, with optional symbols indicating cardinality (the number of instances of one entity related to instances of another entity).
• Keys: Keys are attributes that uniquely identify each entity instance within an entity set. Primary keys are underlined in E/R diagrams to signify their uniqueness.

Special Types of People

Objective: Modify your "people" database to include specific types such as females, males, and parents.

Steps to Solve:

1. Identify the Base Entity:

• Start with the People entity, which includes common attributes like PersonID and Name.

2. Create Subclasses for Gender:

• Introduce Female and Male subclasses that inherit from the People entity. This allows for distinguishing between different genders within the database schema.

3. Define Relationships for Parents:

• Introduce a binary relationship IsParentOf to denote parental relationships between individuals.
• Optionally, consider creating a Parent subclass to explicitly define entities designated as parents.

Detailed Explanation:

In this exercise, the primary goal is to extend the basic "people" database to include additional classifications and relationships.

Entities and Relationships:

• Attributes: PersonID, Name, Gender
• Inherits from : People
• Attributes: PersonID
• Inherits from: People

IsParentOf:

• Attributes: ParentID, ChildID

By introducing subclasses such as Female and Male, you establish a hierarchical structure that simplifies querying and organizing data based on gender-specific attributes. The IsParentOf relationship allows you to explicitly define parental connections, thereby enhancing the database's ability to represent familial relationships effectively.

Example E/R Diagram:

This diagram illustrates how subclasses (Female and Male) inherit attributes from the base entity (People) and how relationships (IsParentOf) connect individuals based on parental roles.

Ternary Relationship to Binary Relationships

Objective: Represent family relationships using a ternary relationship and then convert it into binary relationships.

1. Define the Ternary Relationship:

• Create a ternary relationship Family with attributes Person, Mother, and Father to represent familial connections involving parents and their children.

2. Decompose into Binary Relationships:

• Introduce an intermediary entity FamilyUnit.
• Define binary relationships HasMother and HasFather to replace the original ternary relationship.

The exercise focuses on transforming a complex ternary relationship into simpler binary relationships, which enhances the database's clarity and reduces redundancy.

Family (Ternary Relationship):

• Attributes: Person, Mother, Father

FamilyUnit (Entity):

• Attributes: FamilyID

HasMother (Binary Relationship):

• Attributes: FamilyID, MotherID

HasFather (Binary Relationship):

• Attributes: FamilyID, FatherID

By decomposing the ternary relationship (Family) into two binary relationships (HasMother and HasFather) mediated by the FamilyUnit entity, you streamline the database structure. This approach not only simplifies queries but also maintains data integrity by clearly defining parental roles and relationships.

Ternary Relationship:

Binary Relationships:

This diagram illustrates the transformation from a ternary relationship (Family) to two binary relationships (HasMother and HasFather), demonstrating how entities (FamilyUnit) mediate relationships between individuals (mothers and fathers) within family units.

University Registrar Database

Objective: Design a comprehensive database for a university registrar, including information about students, departments, professors, courses, enrollments, and more.

1. Identify Core Entities:

• Define entities such as Students, Departments, Professors, Courses, and Grades to encompass essential components of a university registrar system.

2. Establish Relationships:

• Create relationships (Enrolled, Teaches, TAFor, Offers) to connect entities and represent interactions such as student enrollments, professor assignments, TA roles, and course offerings.

3. Consider Additional Attributes:

• Include attributes such as grades (GradeID, Grade) to capture academic performance and progress within the database schema.

Designing a university registrar database involves structuring entities and relationships to effectively manage and organize academic information.

• Attributes: StudentID, Name, etc.

Departments:

• Attributes: DepartmentID, Name, etc.

Professors:

• Attributes: ProfessorID, Name, etc.
• Attributes: CourseID, Title, etc.
• Attributes: GradeID, Grade, etc.

Relationships:

• Attributes: StudentID, CourseID, GradeID
• Attributes: ProfessorID, CourseID
• Attributes: StudentID, CourseID
• Attributes: DepartmentID, CourseID

By establishing relationships such as Enrolled (to track student enrollments), Teaches (to identify which professors teach which courses), TAFor (to designate TAs for specific courses), and Offers (to denote courses offered by departments), the database efficiently manages academic operations and facilitates data retrieval and analysis.

Students (Entity):

Departments (Entity):

Professors (Entity):

Courses (Entity):

Grades (Entity):

Enrolled (Relationship):

Teaches (Relationship):

TAFor (Relationship):

Offers (Relationship):

This diagram illustrates the interconnectedness of entities (Students, Departments, Professors, Courses, Grades) and their relationships (Enrolled, Teaches, TAFor, Offers) within a university registrar database, highlighting how data flows between different components to support academic operations.

Decomposing E/R Diagrams

Objective: Decompose a complex four-way relationship into simpler binary and ternary relationships.

1. Identify the Four-Way Relationship:

• Analyze the complex relationship involving Movie, Actor, Director, and Studio to understand their interactions and dependencies.

2. Decompose into Simpler Relationships:

• Decompose the complex relationship into binary relationships (ActsIn, DirectedBy) and a ternary relationship (ProducedBy) to streamline the database structure.

In this exercise, the goal is to simplify a convoluted relationship structure by breaking it down into more manageable components.

• Attributes: MovieID, Title, etc.
• Attributes: ActorID, Name, etc.
• Attributes: DirectorID, Name, etc.
• Attributes: StudioID, Name, etc.
• Attributes: ActorID, MovieID

DirectedBy:

• Attributes: DirectorID, MovieID

ProducedBy:

• Attributes: StudioID, MovieID

By decomposing the complex four-way relationship (Movie, Actor, Director, Studio) into three distinct relationships (ActsIn, DirectedBy, ProducedBy), you enhance the database's clarity and maintainability. Each relationship now focuses on a specific aspect of the movie production process, facilitating easier data management and query operations.

Movie (Entity):

Actor (Entity):

Director (Entity):

Studio (Entity):

ActsIn (Relationship):

DirectedBy (Relationship):

ProducedBy (Relationship):

This diagram illustrates the simplified relationships (ActsIn, DirectedBy, ProducedBy) between entities (Movie, Actor, Director, Studio), ensuring clarity and coherence in representing the movie production process within the database.

Mastering database design, particularly through the creation of effective Entity-Relationship (E/R) diagrams, is crucial for anyone involved in managing or developing database systems. This blog has provided a practical approach to enhancing your skills in database design:

In one scenario, we extended a basic database schema (People) to accommodate specific classifications (Female, Male) and relationships (IsParentOf). This allowed for a clearer representation of familial roles and genders within the database structure.

Another task involved transforming a complex ternary relationship (Family) into simpler binary relationships (HasMother, HasFather) using an intermediary entity (FamilyUnit). This restructuring streamlined the representation of familial connections, improving database clarity and management.

Additionally, designing a comprehensive university registrar database included defining essential entities (Students, Departments, Professors, Courses, Grades) and establishing relationships (Enrolled, Teaches, TAFor, Offers). This approach ensures efficient management of academic operations from enrollment tracking to course offerings.

Lastly, decomposing a complex four-way relationship (Movie, Actor, Director, Studio) into binary and ternary relationships (ActsIn, DirectedBy, ProducedBy) enhanced database clarity and maintainability. This strategy simplified how entities interacted within the database, supporting better data management and retrieval.

By applying these principles and techniques, you'll develop a stronger foundation in database design. Understanding how to structure entities and relationships effectively is essential for creating databases that are well-organized, efficient, and capable of handling complex data interactions. Continuous practice and a thorough grasp of database design concepts will further refine your skills in this critical area of information technology. Happy designing!

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E/r diagram assignment solutions: practical exercises and techniques submit your homework, attached files.

Entity Relationship (ER) Diagram Model with DBMS Example

What is ER Diagram?

ER Diagram stands for Entity Relationship Diagram, also known as ERD is a diagram that displays the relationship of entity sets stored in a database. In other words, ER diagrams help to explain the logical structure of databases. ER diagrams are created based on three basic concepts: entities, attributes and relationships.

ER Diagrams contain different symbols that use rectangles to represent entities, ovals to define attributes and diamond shapes to represent relationships.

At first look, an ER diagram looks very similar to the flowchart. However, ER Diagram includes many specialized symbols, and its meanings make this model unique. The purpose of ER Diagram is to represent the entity framework infrastructure.

What is ER Model?

ER Model stands for Entity Relationship Model is a high-level conceptual data model diagram. ER model helps to systematically analyze data requirements to produce a well-designed database. The ER Model represents real-world entities and the relationships between them. Creating an ER Model in DBMS is considered as a best practice before implementing your database.

ER Modeling helps you to analyze data requirements systematically to produce a well-designed database. So, it is considered a best practice to complete ER modeling before implementing your database.

History of ER models

ER diagrams are visual tools that are helpful to represent the ER model. Peter Chen proposed ER Diagram in 1971 to create a uniform convention that can be used for relational databases and networks. He aimed to use an ER model as a conceptual modeling approach.

Why use ER Diagrams?

Here, are prime reasons for using the ER Diagram

• Helps you to define terms related to entity relationship modeling
• Provide a preview of how all your tables should connect, what fields are going to be on each table
• Helps to describe entities, attributes, relationships
• ER diagrams are translatable into relational tables which allows you to build databases quickly
• ER diagrams can be used by database designers as a blueprint for implementing data in specific software applications
• The database designer gains a better understanding of the information to be contained in the database with the help of ERP diagram
• ERD Diagram allows you to communicate with the logical structure of the database to users

Facts about ER Diagram Model

Now in this ERD Diagram Tutorial, let’s check out some interesting facts about ER Diagram Model:

• ER model allows you to draw Database Design
• It is an easy to use graphical tool for modeling data
• Widely used in Database Design
• It is a GUI representation of the logical structure of a Database
• It helps you to identifies the entities which exist in a system and the relationships between those entities
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ER Diagrams Symbols & Notations

Entity Relationship Diagram Symbols & Notations mainly contains three basic symbols which are rectangle, oval and diamond to represent relationships between elements, entities and attributes. There are some sub-elements which are based on main elements in ERD Diagram. ER Diagram is a visual representation of data that describes how data is related to each other using different ERD Symbols and Notations.

Following are the main components and its symbols in ER Diagrams:

• Rectangles: This Entity Relationship Diagram symbol represents entity types
• Ellipses : Symbol represent attributes
• Diamonds: This symbol represents relationship types
• Lines: It links attributes to entity types and entity types with other relationship types
• Primary key: attributes are underlined
• Double Ellipses: Represent multi-valued attributes

Components of the ER Diagram

This model is based on three basic concepts:

• Relationships

ER Diagram Examples

For example, in a University database, we might have entities for Students, Courses, and Lecturers. Students entity can have attributes like Rollno, Name, and DeptID. They might have relationships with Courses and Lecturers.

WHAT IS ENTITY?

A real-world thing either living or non-living that is easily recognizable and nonrecognizable. It is anything in the enterprise that is to be represented in our database. It may be a physical thing or simply a fact about the enterprise or an event that happens in the real world.

An entity can be place, person, object, event or a concept, which stores data in the database. The characteristics of entities are must have an attribute, and a unique key. Every entity is made up of some ‘attributes’ which represent that entity.

Examples of entities:

• Person: Employee, Student, Patient
• Place: Store, Building
• Object: Machine, product, and Car
• Event: Sale, Registration, Renewal
• Concept: Account, Course

Notation of an Entity

An entity set is a group of similar kind of entities. It may contain entities with attribute sharing similar values. Entities are represented by their properties, which also called attributes. All attributes have their separate values. For example, a student entity may have a name, age, class, as attributes.

Example of Entities:

A university may have some departments. All these departments employ various lecturers and offer several programs.

Relationship

Relationship is nothing but an association among two or more entities. E.g., Tom works in the Chemistry department.

Entities take part in relationships. We can often identify relationships with verbs or verb phrases.

For example:

• You are attending this lecture
• I am giving the lecture
• Just loke entities, we can classify relationships according to relationship-types:
• A student attends a lecture
• A lecturer is giving a lecture.

Weak Entities

A weak entity is a type of entity which doesn’t have its key attribute. It can be identified uniquely by considering the primary key of another entity. For that, weak entity sets need to have participation.

In above ER Diagram examples, “Trans No” is a discriminator within a group of transactions in an ATM.

Let’s learn more about a weak entity by comparing it with a Strong Entity

It is a single-valued property of either an entity-type or a relationship-type.

For example, a lecture might have attributes: time, date, duration, place, etc.

An attribute in ER Diagram examples, is represented by an Ellipse

Cardinality

Defines the numerical attributes of the relationship between two entities or entity sets.

Different types of cardinal relationships are:

• One-to-One Relationships
• One-to-Many Relationships
• May to One Relationships
• Many-to-Many Relationships

1.One-to-one:

One entity from entity set X can be associated with at most one entity of entity set Y and vice versa.

Example: One student can register for numerous courses. However, all those courses have a single line back to that one student.

2.One-to-many:

One entity from entity set X can be associated with multiple entities of entity set Y, but an entity from entity set Y can be associated with at least one entity.

For example, one class is consisting of multiple students.

3. Many to One

More than one entity from entity set X can be associated with at most one entity of entity set Y. However, an entity from entity set Y may or may not be associated with more than one entity from entity set X.

For example, many students belong to the same class.

4. Many to Many:

One entity from X can be associated with more than one entity from Y and vice versa.

For example, Students as a group are associated with multiple faculty members, and faculty members can be associated with multiple students.

How to Create an Entity Relationship Diagram (ERD)

Now in this ERD Diagram Tutorial, we will learn how to create an ER Diagram. Following are the steps to create an ER Diagram:

Let’s study them with an Entity Relationship Diagram Example:

Step 1) Entity Identification

We have three entities

Step 2) Relationship Identification

We have the following two relationships

• The student is assigned a course
• Professor delivers a course

Step 3) Cardinality Identification

For them problem statement we know that,

• A student can be assigned multiple courses
• A Professor can deliver only one course

Step 4) Identify Attributes

You need to study the files, forms, reports, data currently maintained by the organization to identify attributes. You can also conduct interviews with various stakeholders to identify entities. Initially, it’s important to identify the attributes without mapping them to a particular entity.

Once, you have a list of Attributes, you need to map them to the identified entities. Ensure an attribute is to be paired with exactly one entity. If you think an attribute should belong to more than one entity, use a modifier to make it unique.

Once the mapping is done, identify the primary Keys. If a unique key is not readily available, create one.

For Course Entity, attributes could be Duration, Credits, Assignments, etc. For the sake of ease we have considered just one attribute.

Step 5) Create the ERD Diagram

A more modern representation of Entity Relationship Diagram Example

Best Practices for Developing Effective ER Diagrams

Here are some best practice or example for Developing Effective ER Diagrams.

• Eliminate any redundant entities or relationships
• You need to make sure that all your entities and relationships are properly labeled
• There may be various valid approaches to an ER diagram. You need to make sure that the ER diagram supports all the data you need to store
• You should assure that each entity only appears a single time in the ER diagram
• Name every relationship, entity, and attribute are represented on your diagram
• Never connect relationships to each other
• You should use colors to highlight important portions of the ER diagram
• ER Model in DBMS stands for an Entity-Relationship model
• The ER model is a high-level data model diagram
• ER diagrams are a visual tool which is helpful to represent the ER model
• ER diagrams in DBMS are blueprint of a database
• Entity relationship diagram DBMS displays the relationships of entity set stored in a database
• ER diagrams help you to define terms related to entity relationship modeling
• ER Model in DBMS is based on three basic concepts: Entities, Attributes & Relationships
• An entity can be place, person, object, event or a concept, which stores data in the database (DBMS)
• Relationship is nothing but an association among two or more entities
• A weak entity is a type of entity which doesn’t have its key attribute
• It is a single-valued property of either an entity-type or a relationship-type
• It helps you to defines the numerical attributes of the relationship between two entities or entity sets
• ER- Diagram DBMS is a visual representation of data that describe how data is related to each other
• While Drawing ER diagrams in DBMS, you need to make sure all your entities and relationships are properly labeled.

Explaining an ER Diagram, With Steps and Use Cases

Sudip is a TOGAF Certified Solutions Architect with more than 15 years spent in the IT industry. He is now a full-time freelance technical writer and has contributed to several publications on various topics including the cloud, DevOps, SaaS, and cybersecurity. When not reading or writing, he is found playing a game of chess or in a squash court.

• Entity-Relationship Diagram
• Vertabelo Features

Get to know what an ER Diagram is through use cases and examples. Explore the notations for the essential components of an ERD.

Entity-relationship diagrams (ERDs) are used to visualize data and relationships among the entities of a system. At its core, an ER Diagram explains the logical structure and the flow of information within a data model. To do so, an entity-relationship diagram highlights entities, attributes , and relationships through predefined symbols for effective visualization of the architecture. Preparing an ERD is an essential first step towards designing a database, helping to analyze data flow and helping with due diligence of related system requirements.

When you Need an ER Diagram

An ER diagram is used to design database data models. If you are designing a new data model, preparing an ER Diagram helps with essential due diligence to capture and document system requirements. While in production, an ER diagram acts as a reference to improve database throughput , debug errors , and redesign architecture .

In addition to technical references, as ERDs are conceptual blueprint of the data flow within a system, they are also used to streamline business processes by identifying redundancies and bottlenecks within business entities.

In this article, we will go through a few ER diagram examples and how you can use Vertabelo to create ER diagrams to design efficient data models.

Objects in ER Diagrams

While there are several notations, the crow’s foot notation (also known as the information engineering notation or the IE notation) is prominently used in ER modeling due to its intuitive format and symbols. Let us delve into the representation of entities and relationships in crow’s foot notation to help model an ER diagram.

Entities represent data components within a database that could be living or non-living, real or abstract, so long as their data is stored in the database. Examples of entities include people, places, objects, events, or concepts. In ER diagrams, entities are usually depicted by rectangles, with the entity name at the top.

Client, City and Country Entities of a Data Model

An attribute is a description of the properties of an entity or relationship. For instance, the entity shipment could have attributes such as shipment ID ( id ), client_id , shipment time_created , billing_address , etc. In the crow’s foot notation, an attribute is represented as a line of text in the lower compartment of the corresponding entity’s rectangle.

A Snapshot Showing Various Attributes of the shipment Entity

Relationship

A relationship denotes how various entities interact with each other. For instance, in a database for a vehicle hiring service, a customer will form a relationship with the entity vehicle through the act of selecting . “Select” is, therefore, a relationship between the two entities.

The relationship between data in one table and data in another table is called cardinality . Specifically, the cardinality indicates the number of times one entity in a table can relate with the instances of another entity.

When drawing relationships in crow’s foot notation, there are two indicators: one for multiplicity (cardinality) while the other indicates whether a relationship is optional or mandatory. A mandatory relationship is shown by a line perpendicular to the relationship line, while an optional relationship is shown by an empty circle.

When drawing relationships in crow’s foot notation, there are two indicators: one for multiplicity (cardinality) while the other indicates whether a relationship is optional or mandatory. A mandatory relationship is shown by a line perpendicular to the relationship line, while an optional relationship is shown by an empty circle.

In data modeling, there are three types of cardinalities.

In a one-to-one association, one entity in a table can relate only once to an entity in another table. For instance, a customer can hire only one vehicle at a time, and a vehicle can be assigned to only one customer at a time.

In an entity-relationship diagram, one row in one table would correlate to only one row in another table. In the IE notation, a mandatory one-to-one relationship is represented by two lines perpendicular to the relationship line near both entity rectangles.

One-to-One Association With Mandatory Relationship

One-to-One Association With Optional Relationship

One-to-Many

A one-to-many relationship occurs when one instance of an entity can interact with multiple instances of another entity. For instance, one customer can hire several vehicles, while each vehicle can only be assigned to one customer at a time.

In the IE notation, a one-to-many relationship is represented by a single line at the end of the single instance, and a three-pronged crow’s-foot symbol facing the multiple instance rectangle.

One-to-Many Association With Mandatory Relationship

Many-to-Many

This type of cardinality occurs when multiple instances of one entity can relate with more than one instance of another set of entities. Imagine a scenario in which a customer could select multiple vehicles, and a vehicle could be leased by multiple customers within a certain time period. In the IE notation, a many-to-many relationship is depicted by crow’s feet at both ends of the relationship line.

Many-to-Many Association With Mandatory Relationship

Many-to-Many Association With Optional Relationship

While the above notations are in crow’s foot notation, there are a number of other ERD notation formats, the details of which can be found here .

Types of Data Models

There are three types of data models in ER modeling.

Conceptual and Logical Data Models 

The conceptual and logical data models describe how information is organized in a system regardless of the database used. The logical model specifies entities, attributes, and relationships between entities. It abstracts away from actual DBMS used in the implementation of the system.

Physical Data Model

The physical data model represents how the model will be built in the database. It shows the full table definition, including column names, column data types, table constraints, the primary key, the foreign keys, and the relationships between tables. The physical data model will be different for different RDBMS. For example, the data type for a given column may be different between MySQL and SQL Server.

This section appears incomplete. There is no explanation of what a conceptual model is (as opposed to logical). Also, the last sentence is incomplete. here .-->

How to Draw an ER Diagram

Let’s create an ER diagram for a data model using Vertabelo . Consider a simple scenario in which a client orders food at a restaurant. The client must purchase one or more menu items, while each menu item is served by one attendant.

1. First, identify the entities in your database. In this case, we have three entities: Client , Menu_Item , and Attendant .

2. The second step involves identifying the relationships between the selected entities.

• The Client is served a Menu_Item .
• The Attendant delivers the Menu_Item .

3. The third step involves identifying cardinalities .

• A Client can be assigned multiple Menu_Item s.
• An Attendant can only deliver one Menu_Item at a time before taking another order from the same Client (assumption) .

4. The fourth step is identifying entity attributes . Make sure that every attribute is mapped to only one entity; assign modifiers for those that belong to more than one.

Specify the primary key for each entity by using the most uniquely identifying attributes.

Setting the Attributes of an Entity Using the Vertabelo Property Editor

5. Once you have identified the entities, relationships, cardinalities, and attributes, you can now create your ER diagram. Here’s what our sample project will look like when designed using the crow’s foot (IE) notation.

Disclaimer: All the above diagrams were created using Vertabelo .

Data modeling challenges in the real world are often complex. Creating a precise ER diagram requires not only the right knowledge but also the right tools. Whether you are learning or designing a data model, Vertabelo acts as a great resource to your ERD designing needs. To find out more about Vertabelo features and how it can help, visit this article .

ER Diagram Example Use Cases

Let’s look at a few examples of the entity-relationship diagram to understand its use cases better.

Use Case: Data Model for a Freelancers Collective

You can find a detailed discussion of this ER diagram in A Data Model for a Freelancers Collective .

This model shows the logical structure that can be used in large freelance projects that require collaboration between distributed teams. Since the freelance world connects professionals in a wide range of fields with varying skill sets, you will need a tool to orchestrate the interactions among freelancers, teams, and clients. Let’s consider the Freelancer Collective platform as a project management solution that helps connect various actors to collaborate on a number of projects.

Our model is broken into four main subject areas: Freelancers , Customers & Projects , Teams , and Project Phases .

The Freelancers section includes all the information provided by freelancers when they register to use the application. The information relevant to our database includes the freelancer’s skills, skill level, and skill sets. We also need to understand the freelancer’s availability to be sure that they can deliver an assigned project.

The second focus area is Customers & Projects . Customers use the system to upload their projects and connect with freelancers. This section includes the customer , project , project_status_history , skill , and project_outcome tables. Customers have also registered to use the application, and the system extracts their details from a special form. Project details are revealed when the client posts a project.

The third section is for the teams . This subject area forms a team and assigns them a project based on the freelancer’s ability and skill sets. The team is the major entity for this section. Other tables in this section include team_member , in_charge , freelancer , phase_plan , and project .

The final section involves the Project phases . Some entities in this section have appeared in other subject areas, and these include freelancer , customer , project_outcome , and project . The new entities in this set include phase_history , phase_catalog , and phase_plan .

Relationships

When a client posts a project, the system checks for the skill requirements and the availability of freelancers. The system then creates a team of freelancers who will collaborate on the project, which is now divided into phases. This system works as a supervisor, looking for the best collective that will work on a project, and assigning different project phases to different freelancers depending on the availability and skill level.

Collectively, this is how the data model can look:

Use Case: Peer-to-Peer Lending Data Model

You can find a detailed discussion of this ER diagram in A Peer-to-Peer Lending Platform Data Model .

Peer-to-peer lending refers to the practice of multiple lenders and borrowers transacting through a common platform. A peer-to-peer lending platform here essentially acts as a liaison between the parties to enable the process of lending, while ensuring necessary compliance and maintaining data security of all parties.

Let’s understand the data model by considering a scenario.

The entities are the following:

• A borrower requests a loan of a specific amount through the peer-to-peer lending platform after submitting details of his credit score, default history, tax returns, etc. Additional details of the loan may include repayment duration and preferred interest rate window.
• The lender(s) register(s) on the platform by entering its respective financial details, including KYC, tax returns, etc. It also enters its lending preferences, including the loan duration, interest rate, amount, borrower credit score, etc.

The borrower asks for funding from an investor, who releases the funds through the loan fulfilment and repayment subsystem. This subsystem forms an associative relationship between the two entities.

The lending platform here essentially acts as the interface, connecting would-be investors with potential borrowers. This reduces the complexity of access to financing by allowing users to determine their own lending rates. The data model that can support this platform is outlined below:

An ER Diagram Is a Must

An ER diagram provides an easy way to represent your data model at a higher level of abstraction. With marked-up relationships among data sets, an ER diagram is perfect for process modeling and system debugging. In this article, we discussed the core concepts of ER modeling, with practical examples using Vertabelo for pragmatic experience. Whether you are learning or working on real-time data modeling, creating an ER diagram is a must.

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What is an Entity Relationship Diagram (ERD)? | An Introduction to ER Diagram

So you want to learn Entity Relationship diagrams? This ER diagram tutorial will cover their usage, history, symbols, notations and how to use our ER diagram software to draw them. We’ve also added some templates for you to get started quickly.

What is an ER diagram?

An Entity Relationship Diagram (ERD) is a visual representation of different entities within a system and how they relate to each other . It is a tool used to design and model relational databases, and shows the logical structure of the database. ER diagrams use symbols to represent entities, attributes, and relationships, which help to illustrate the relationships between the entities in the database. It consists of entities (which represent objects or concepts, like “Customer” or “Product”) and relationships (which represent how these entities are connected or interact with each other, like “owns” or “buys”).

Entities are depicted as rectangles, and relationships are shown as diamonds. Lines connecting entities and relationships represent the connections between them, often indicating the type of relationship (such as one-to-one, one-to-many, or many-to-many).

ER diagrams are commonly used in software engineering and database design to help developers and stakeholders understand and design complex databases. For example, the elements writer, novel, and a consumer may be described using ER diagrams the following way:

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History of ER Diagrams

ER diagrams were first introduced by a computer scientist named Peter Chen in 1976. He proposed them as a way to visually represent the structure of databases. During the late 1970s and early 1980s, ER diagrams became widely used in both academic and industrial settings. They provided a clear way to show how different pieces of information are related to each other.

As database systems became more complex, ER diagrams remained important tools for designing and managing databases. They helped developers and users understand how data was organized and connected.

In the 1990s and 2000s, with the rise of the internet and new technologies, ER diagrams adapted to accommodate these changes. They continued to be essential for designing databases, but they were sometimes used alongside other modeling techniques.

Today, ER diagrams are still widely used in software engineering and database design. They provide a simple and intuitive way to plan and communicate the structure of databases, making them valuable tools for developers and designers.

ER Diagram Templates

Below are some ER diagram templates so you can get started quickly. Clicking on the image and in the new page that opens click the “Use as Template” button. For more templates check our ER diagram template section .

Uses of ER Diagrams?

ER diagrams are essential tools for designing, communicating, maintaining, and optimizing databases. They facilitate collaboration, ensure data integrity, and contribute to the efficient management of database systems. Here are several uses of ER diagrams.

Database design: ER diagrams are used to design databases. They provide a visual representation of how different pieces of information, called entities, are related to each other. This helps in planning the structure of the database before it’s built.

Communication: ER diagrams act as a common language between people involved in developing databases, such as developers, designers, and clients. They help everyone understand how the database will work and how data will be organized.

Database maintenance: Even after a database is created, ER diagrams remain useful for maintenance. They help developers understand the existing structure and make changes or updates as needed while ensuring the integrity of the database.

Documentation: ER diagrams serve as documentation for the database system. They provide a detailed overview of the database schema, including entities, attributes, and relationships. This documentation helps in troubleshooting issues and training new team members.

Identifying redundancy and inconsistencies: By visualizing relationships between entities, ER diagrams help identify redundant or inconsistent data in the database design. This allows for optimization and ensures data accuracy.

Database optimization: ER diagrams aid in optimizing database performance. By understanding entity relationships, developers can design efficient queries and data retrieval strategies, leading to improved performance and scalability.

Integration with development tools: ER diagrams can be integrated into various development tools and database management systems. Many software tools provide features for creating, editing, and generating code from ER diagrams, streamlining the database development process.

The Components and Features of ER Diagrams

An entity represents a real-world object, concept, or thing about which data is stored in the database. It could be a person, place, thing, event, or concept.

Characteristics

Attributes: Entities have attributes that describe their properties or characteristics. Instances: Each entity has instances or occurrences, representing individual occurrences of the entity in the real world. Identity: Each instance of an entity is uniquely identifiable and can be distinguished from other instances. Relationships: Entities can be related to other entities through relationships, forming connections within the database schema.

Types of entities

Strong entities: Also known as regular entities, these entities have attributes that uniquely identify each instance. They can exist independently of other entities. Weak entities: Weak entities do not have a primary key attribute of their own and depend on a related strong entity (owner entity) for their existence. They are identified by their relationship with the owner entity. Associative entities: Also called many-to-many entities, these entities are used to represent relationships between relationships. They arise in many-to-many relationships and typically contain attributes in addition to the foreign keys linking the associated entities.

Types of entity keys

Simple key: A single attribute serves as the primary key. Composite key: A combination of two or more attributes serves as the primary key. It is used when no single attribute uniquely identifies each instance. Surrogate key: An artificially generated identifier, such as an auto-incremented integer, is used as the primary key. It is often added when no suitable natural key exists or when there are concerns about stability or size of natural keys.

Attributes are the characteristics or properties of entities. They describe the details of each entity. For example, attributes of a “Customer” entity might include “Customer ID,” “Name,” and “Email Address.”

Name: Each attribute has a name that identifies it within the entity. Data type: Attributes have a data type that specifies the kind of data they can hold, such as text, number, date, etc. Constraints: Attributes may have constraints that define rules or conditions for the values they can contain, such as uniqueness or requiredness. Domain: Attributes have a domain, which is the set of all possible values that the attribute can take. Nullability: Attributes may allow null values, meaning they can have no value assigned to them for some instances of the entity.

Types of attributes

Simple attribute: A single atomic value is stored in the attribute. Example: Name, Age. Composite attribute: An attribute that can be divided into smaller sub-parts, each representing a distinct attribute. Example: Address (composed of Street, City, Zip Code). Single-valued attribute: An attribute that holds a single value for each instance of the entity. Multi-valued attribute: An attribute that can hold multiple values for each instance of the entity. Example: Phone Numbers.

Relationships

Relationships show how entities are connected or related to each other in the database. They represent interactions or associations between entities. Examples include “owns,” “buys,” or “works for.”

Name: Each relationship has a name that describes the nature of the association between entities. Directionality: Relationships can be unidirectional or bidirectional, indicating the flow or direction of the association between entities. Cardinality: Cardinality specifies the number of instances of one entity that can be associated with instances of another entity in a relationship. It defines the minimum and maximum occurrences of related entities. Degree: The degree of a relationship indicates the number of entities participating in the relationship. Relationships can be unary (involving a single entity), binary (involving two entities), ternary (involving three entities), etc. Attributes: Relationships can have attributes that describe additional information or properties about the association between entities. Recursive relationships: Some relationships involve an entity being related to itself, known as recursive relationships. They represent connections or interactions within the same entity.

Types of relationships

One-to-one (1:1): Each instance of one entity is associated with exactly one instance of another entity. One-to-many (1:N): Each instance of one entity is associated with multiple instances of another entity, but each instance of the other entity is associated with only one instance of the first entity. Many-to-one (N:1): Multiple instances of one entity are associated with exactly one instance of another entity. Many-to-many (M:N): Multiple instances of one entity are associated with multiple instances of another entity, and vice versa. Recursive relationships: An entity is related to itself through a relationship. This can represent hierarchical structures or self-referential associations.

Cardinality

Cardinality specifies the number of instances of one entity that can be associated with the number of instances of another entity in a relationship. It describes the minimum and maximum number of occurrences of one entity that can be associated with occurrences of another entity.

Minimum cardinality: Specifies the minimum number of instances required in a relationship. Maximum cardinality: Indicates the maximum number of instances allowed in a relationship. Directionality: Determines if the relationship is one-way or two-way. Completeness: Shows whether participation in the relationship is mandatory or optional. Multiplicity: Defines the range of valid occurrences for each entity. Constraint enforcement: Ensures data integrity by enforcing rules on entity participation.

Entity Relationship Diagram (ERD) Symbols and Notations

There are three basic elements in an ER Diagram: entity, attribute, relationship. There are more elements which are based on the main elements. They are weak entity, multi valued attribute, derived attribute, weak relationship, and recursive relationship. Cardinality and ordinality are two other notations used in ER diagrams to further define relationships.

An entity can be a person, place, event, or object that is relevant to a given system. For example, a school system may include students, teachers, major courses, subjects, fees, and other items. Entities are represented in ER diagrams by a rectangle and named using singular nouns.

Weak Entity

A weak entity is an entity that depends on the existence of another entity. In more technical terms it can be defined as an entity that cannot be identified by its own attributes. It uses a foreign key combined with its attributed to form the primary key. An entity like order item is a good example for this. The order item will be meaningless without an order so it depends on the existence of the order.

An attribute is a property, trait, or characteristic of an entity, relationship, or another attribute. For example, the attribute Inventory Item Name is an attribute of the entity Inventory Item. An entity can have as many attributes as necessary. Meanwhile, attributes can also have their own specific attributes. For example, the attribute “customer address” can have the attributes number, street, city, and state. These are called composite attributes. Note that some top level ER diagrams do not show attributes for the sake of simplicity. In those that do, however, attributes are represented by oval shapes.

Multivalued Attribute

If an attribute can have more than one value it is called a multi valued attribute. It is important to note that this is different from an attribute having its own attributes. For example, a teacher entity can have multiple subject values.

Derived Attribute

An attribute based on another attribute. This is found rarely in ER diagrams. For example, for a circle, the area can be derived from the radius.

Relationship

A relationship describes how entities interact. For example, the entity “Carpenter” may be related to the entity “table” by the relationship “builds” or “makes”. Relationships are represented by diamond shapes and are labeled using verbs.

Recursive Relationship

If the same entity participates more than once in a relationship it is known as a recursive relationship. In the below example an employee can be a supervisor and be supervised, so there is a recursive relationship.

Cardinality and Ordinality

These two further defines relationships between entities by placing the relationship in the context of numbers. In an email system, for example, one account can have multiple contacts. The relationship, in this case, follows a “one to many” model. There are a number of notations used to present cardinality in ER diagrams. Chen, UML, Crow’s foot, Bachman are some of the popular notations. Creately supports Chen, UML and Crow’s foot notations.The following example uses UML to show cardinality.

How to Draw ER Diagrams

Below points show how to go about creating an ER diagram.

• Identify all the entities in the system. An entity should appear only once in a particular diagram. Create rectangles for all entities and name them properly.
• Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship.
• Add attributes for entities. Give meaningful attribute names so they can be understood easily.

Sounds simple right? In a complex system, it can be a nightmare to identify relationships. This is something you’ll perfect only with practice.

Conceptual, Logical and Physical Data Models

Conceptual, logical, and physical data models are three distinct stages in the process of designing and implementing a database system. Each model serves a specific purpose and targets different levels of abstraction.

Conceptual Data Model

Purpose: The conceptual data model represents the highest level of abstraction and focuses on understanding the business requirements and concepts without considering implementation details. Characteristics: Describes entities, their attributes, and the relationships between them at a conceptual level. Independent of any specific database management system (DBMS) or technology. Provides a global view of the entire database system without delving into technical details. Representation: Often depicted using Entity-Relationship (ER) diagrams or similar graphical tools. Example: In a university system, the conceptual data model might include entities like Student, Course, and Instructor, along with their attributes and relationships.

Logical Data Model

Purpose: The logical data model translates the conceptual model into a more detailed and structured representation that can be implemented in a specific DBMS. Characteristics: Defines the structure of the database using tables, columns, keys, and relationships. Captures data requirements and relationships more precisely than the conceptual model. Still independent of the physical implementation details such as storage optimizations or indexing strategies. Representation: Often depicted using Entity-Relationship (ER) diagrams or Unified Modeling Language (UML) class diagrams, along with normalization techniques. Example: In the university system, the logical data model would specify tables like Student, Course, and Instructor, along with their attributes and primary/foreign keys.

Physical Data Model

Purpose: The physical data model represents the actual implementation of the database design in a specific DBMS, considering storage structures, indexing strategies, and optimization techniques. Characteristics: Translates the logical data model into a schema that can be directly implemented in a DBMS. Specifies details such as data types, indexes, partitions, and storage allocation. Optimized for performance, scalability, and efficiency based on the requirements of the application and the capabilities of the chosen DBMS. Representation: Often represented using Data Definition Language (DDL) scripts or database schema diagrams specific to the chosen DBMS. Example: In the university system, the physical data model would include details like table definitions with specific data types, indexes on frequently queried columns, and partitioning strategies for large tables.

Limitations of ER Diagrams

While Entity-Relationship diagrams are widely used for database design and modeling, they do have some limitations:

ER diagrams can get really complicated, especially in big systems with lots of entities and relationships. It can be tough to manage and understand these complicated diagrams, making it harder to see how the database works overall.

Sometimes ER diagrams don’t capture everything about the real world accurately. This can happen if the descriptions used to make the diagrams aren’t clear or if there are differences in how people understand things. It can lead to mistakes or confusion in the diagram.

ER diagrams focus on the big picture of the database structure, but they might miss out on some of the smaller details, like how the data is actually stored or used. This means they might not show everything about how the database works.

ER diagrams have trouble showing certain kinds of relationships or rules well. For example, really complicated structures or rules about time or space can be hard to draw accurately using ER diagrams.

ER diagrams might not be great at showing certain ideas from object-oriented programming, like inheritance or polymorphism. It can be tricky to translate these ideas into ER diagrams, and it might need extra explanations or changes to make them work.

As databases change over time, ER diagrams might need to be updated to show the changes accurately. Keeping track of these changes and making sure the diagrams match the actual database can take a lot of time and effort.

ER Diagram Best Practices

Provide a precise and appropriate name for each entity, attribute, and relationship in the diagram. Terms that are simple and familiar always beats vague, technical-sounding words. In naming entities, remember to use singular nouns. However, adjectives may be used to distinguish entities belonging to the same class (part-time employee and full-time employee, for example). Meanwhile attribute names must be meaningful, unique, system-independent, and easily understandable.

Remove vague, redundant or unnecessary relationships between entities.

Never connect a relationship to another relationship.

Make effective use of colors. You can use colors to classify similar entities or to highlight key areas in your diagrams.

Benefits of ER diagrams

ER diagrams constitute a very useful framework for creating and manipulating databases. First, ER diagrams are easy to understand and do not require a person to undergo extensive training to be able to work with it efficiently and accurately. This means that designers can use ER diagrams to easily communicate with developers, customers, and end users, regardless of their IT proficiency.

Second, ER diagrams are readily translatable into relational tables which can be used to quickly build databases. In addition, ER diagrams can directly be used by database developers as the blueprint for implementing data in specific software applications.

Lastly, ER diagrams may be applied in other contexts such as describing the different relationships and operations within an organization.

Drawing ER Diagrams Using Creately

You can draw entity relationship diagrams manually, especially when you are just informally showing simple systems to your peers. However, for more complex systems and for external audiences, you need diagramming software such as Creately to craft visually engaging and precise ER diagrams. The ER diagram software offered by Creately as an online service is pretty easy to use and is a lot more affordable than purchasing licensed software. It is also perfectly suited for development teams because of its strong support for collaboration.

FAQs about Entity Relationship Diagrams

Why are er diagrams important, what are the common mistakes to avoid when creating er diagrams.

• Not defining the entities and relationships clearly
• Overcomplicating the diagram by including too many entities and relationships
• Using inconsistent naming conventions for entities and attributes
• Failing to specify cardinality and participation constraints for relationships
• Using unclear or ambiguous symbols or terminology

What types of relationships can be represented in an ER diagram?

ER diagrams can represent several types of relationships, such as:

• one-to-one,
• one-to-many, and
• many-to-many relationships.

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ER Diagram: What Is Entity Relationship Diagram With Examples

This is a comprehensive guide to the Entity-Relationship Diagram or ER Diagram including ER models, tools, symbols, examples and more:

Entity Relationship Diagram (ER Diagram or ERD) is a pictorial or visual representation of classifying groups or entities of common interest and defining the relationship between these groups. Hence, a structure is created with various symbols of different shapes and sizes so that it can be used as a model to depict the internal structure & relationship.

Entity Relationship Diagram is primarily used in the following areas:

• ER Models in Database Design:  Used to visualize database tables and their relationships between them. Also finds usage in database troubleshooting.
• ER Diagrams in Software Engineering: Normally used in the planning stages of a software project. It is used for identifying different system elements and how they interact with each other. Also commonly known as Data Flow Diagrams (DFD).

Table of Contents:

What Is Entity Relationship Model

Why use er diagrams, components of er diagram, er diagrams symbols and notations, cardinality, steps to create an er diagram (erd), er diagram examples, advantages of erd, disadvantages of erd, importance of enhanced er diagram, normalize an er diagram, list of the online er tools, was this helpful, recommended reading, what is an entity relationship diagram.

Entity Relationship Diagram (ERD) was a solution to the problem of not having a standard way to model databases or neither to business processes. Thus, it is a type of flowchart that helps us understand how different entities, objects, or concepts are related to each other within a system.

ER Diagram finds usage in fields such as business information system, software engineering, education & research, etc.

Here ERD or ER models are used through a defined set of symbols such as ovals, diamonds, rectangles, etc., and connecting lines to display the interconnectedness between them. ER Diagrams are also used in conjunction with Data Flow Diagrams (DFD), to show the flow of information within processes or systems.

Entity-Relationship Model (ER Model) is a high-level data model or a graphical approach to database design, which defines the data elements and their relationship within a specified system or software.

ER Diagram is a way of representing ER Model graphically.

History of ER models:

Peter Chen is credited with the development of ER Modelling for database designs in the 1970s, through his 1976 seminal paper titled “The Entity-Relationship Model: Towards a Unified View of Data”.

Later around 1960–70s, Charles Bachman developed a type of Data Structure Diagram, which further contributed to the development of the Unified Modelling Language (UML), widely used in software design.

Suggested Reading =>> Data Modeling Tutorial

They find usage in some of these below key areas:

#1) Business Information Systems

The diagrams help in designing or analyzing relational databases used in the business processes. Any business process that has used fielded data involving entities can benefit from a relational database. It can be used for streamlining processes, and to uncover information more easily, and thus improve results.

#2) Database Troubleshooting

ER diagrams help to analyze existing databases and to identify and resolve problems in database logic or during deployment. Drawing them helps to highlight areas where things may have gone wrong.

#3) Business Process Re-engineering (BPR)

They are used to analyze databases used in business process re-engineering and also during modeling of a new database setup.

#4) Education

They are used in planning data structures for storing relational information and later retrieval from databases.

#5) Research

ER Diagrams are used in setting up databases to analyze structured data.

It comprises:

• Entity: Any object that can have data stored in it.
• Relationships between entities:  Defines how the entities are associated or related with each other.
• Attributes of entities & relationships:  Represents the characteristic or property of an entity.

It is n ormally depicted as Rectangle.

Entity Type: A group of similar entities, which are having similar characteristics.

Entity Set: A particular sub-group within an entity type having a common sub-characteristic.

Entity Categories: It can be categorized as

• Strong Entity
• Weak Entity
• Associative Entity

Difference between Strong and Weak Entity:

Entity Keys: It is an attribute that helps to define an entity uniquely within an entity set.

Entity keys can be categorized as:

• Super key: A set of attributes that helps together define an entity uniquely, within an entity set.
• Primary or Candidate key: A key used to uniquely identify an entity set.
• Foreign key: Helps to identify relationships between entities.

#2) Relationship

It is normally depicted as a diamond.

Difference between Strong and Weak Relationship:

#3) Attributes

It is normally depicted as an oval.

Difference between Key and Partial-key attribute:

Other different attribute types:

#1) Simple attribute

• Attributes that cannot be further divided.
• Example: Aadhar number of any individual.

#2) Composite attribute

• Constitutes of multiple simple attributes.
• Example:  A full name may consist of a combination of First Name & Last Name.

#3) Derived attribute

• Attributes that do not directly exist in the database, but whose values are derived based on user requirements.
• Example:  Age can be derived based on DOB.

#4) Single-value attribute

• Attributes that contain a single value.
• Example: A field to store the Aadhar number of an individual.

#5) Multi-value attribute

• Attributes that contain more than one value.
• Example:  Any individual may have more than one mobile no./email that are required to be stored.

It shows how an entity in one entity set is related to another entity within the same or other entity sets.

Below are some of the different types of cardinal relationships:

#1) One-to-One Relationships

• One entity from an entity set is related to one entity in another entity set.
• For example , A student can register for multiple courses. But for any particular course, it can be traced back to every single student.

#2) One-to-Many Relationships

• One entity from an entity set is related to many entities in another entity set.
• For example , A classroom with multiple students.

#3) Many to One Relationships

• Many entities from an entity set are related to one entity in another entity set.
• For example , many students belong to the same class.

#4) Many-to-Many Relationships

• Many entities from an entity set are related to many entities in another entity set.
• For example , many students associated with multiple faculty members and vice versa.

[image source ]

Below are some of the basic steps:

Entity Relationship Diagram, commonly known as ERD or ER Diagram or ER model, is one type of structural diagram used in database design. It contains different symbols and connectors that help to visualize two important information:

• The major entities present within the system scope
• The inter-relationships among these present entities.

Below is an example of the Loan system ER Diagram:

Entities: i) Borrower ii) Loan Request ii) Lender iv) Intermediary.

Relationship: How the Borrower Loan request is being captured by the lender, and the lending process takes place.

Below is an example of Subject wise Performance ER Diagram.

Entities: i) Students ii) Subject ii) Marks Obtained iv) Teacher.

Relationship: How the Students have performed on each Subject in terms of Marks allotted by the Teacher.

These are enlisted below:

• Offers a visual representation of the overall structure.
• Aids database designers to create an efficient design/architecture.
• Helps to show the flow of data and the working of the entire system.
• Acts as a blueprint for the existing database.
• Aids in effective communication, as readers are able to understand relationships among different fields.
• Provides flexibility in establishing and deriving relationships from the existing ones.
• Good support for DBMS.
• Expression is limited.
• Can be sometimes ambiguous.
• It may not be always concise.
• There are no industry-defined standards for documentation, so it may be confusing sometimes.
• Hard to display information control.
• Some data may be lost or covered up.
• Enhanced Entity Relationship (EER) diagrams represent an expanded version of ER diagrams.
• EER models are more helpful while designing databases with high-level models.
• With more enhanced features, databases can be planned more efficiently by delving into the properties and constraints with much more precision.
• It aids you in having a more detailed look at your information.
• If the database would contain a larger amount of data, then it is advisable to switch to the enhanced model to gain a more deep understanding of your model.

Application or provisioning of normalization leads to more robust requirement analysis, thus helping in overcoming some of the disadvantages.

Below are some of the reasons for the normalization of ERD:

• Helps to improve the conceptual model.
• Aids in speeding up implementation.
• Helps in standardizing organizational vocabulary.
• Enforce business rules.
• Ensures adequate data quality.

Below are some of the basic ways/steps for normalization of ERD:

• Transforming attributes into entity types.
• Splitting compound attributes into further smaller attributes.
• Expanding entity types into more two entity types and a relationship.
• Transforming a weak entity type into a stronger entity type.
• Adding historical details to an existing data model.

Multiple tools are available online for creating and editing ER models. Some of the prominent online tools are as mentioned below:

• Pony ORM : One of the best SQL ORM used for fast prototyping.
• Smartdraw : Easy and powerful for creating perfect layouts.
• ERD Plus : Helps to draw with the step-by-step process explained for any user.
• Lucidchart : Helps to create powerful visuals for every business need.
• Creately : Helps in drawing the most complex data design easily with intuitive features.

Also Read =>> Open source Database Design Tools

• 10 Best Data Modeling Tools To Manage Complex Designs
• 5 Important Diagrams That Testers Need to Learn How to Use
• Dimensional Data Model In Data Warehouse - Tutorial With Examples
• Top 10 Database Design Tools to Build Complex Data Models
• Top 24 Data Modeling Interview Questions with Detailed Answers
• What Is Data Modeling – Conceptual, Logical, Physical Models
• 40+ Best Database Testing Tools - Popular Data Testing Solutions
• Database Normalization Tutorial: 1NF 2NF 3NF BCNF Examples

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A Guide to the Entity Relationship Diagram (ERD)

Learn all about Entity Relationship Diagrams (ERDs), what they are used for, how to understand them, how to create them, and more in this guide.

Table of Contents

What is an Entity Relationship Diagram (ERD)?

An Entity Relationship Diagram (ERD) is a type of diagram that lets you see how different entities (e.g. people, customers, or other objects) relate to each other in an application or a database.

They are created when a new system is being designed so that the development team can understand how to structure the database. They can also be created on an existing system to help the team understand how the system works and to find and resolve any issues.

Entity Relationship Diagrams use a specific set of symbols, such as shapes and arrows, to depict the system and database.

Here’s an example of an ERD:

Components of an ERD

An Entity Relationship Diagram is made up of many different components:

Relationship

An entity is a thing that can have data stored about it. It can be a physical object (e.g. car, person), a concept (e.g. address) or an event (e.g. student enrolment in a course). They represent nouns.

They are usually represented as rectangles on an ERD with the entity name inside the rectangle.

An entity can also be a strong entity or a weak entity. What’s the difference?

A strong entity has an identifier (a primary key) and does not depend on any other entities for it to exist. For example, a student may be a strong entity, as it can have a primary key and does not depend on any other entities for it to exist.

A weak entity is one that depends on a strong entity for existence. This means it has a foreign key to another entity. For example, an enrolment of a student may be a weak entity, as an enrolment cannot exist without a student.

A relationship in an ERD defines how two entities are related to each other. They can be derived from verbs when speaking about a database or a set of entities.

Relationships in ERDs are represented as lines between two entities, and often have a label on the line to further describe the relationship (such as “enrols”, “registers”, “completes”).

There are several types of relationships that are represented on an ERD:

• One to one: One record of an entity is directly related to another record of an entity
• One to many: One record of an entity is related to one or more records of another entity.
• Many to many: Many records of one entity can be related to many records of another entity.

An attribute is a property of an entity or something that can be used to describe an entity. They are often represented as ovals, or as entries inside an entity.

There are several different types of attributes represented on an ERD:

• Simple: an attribute that cannot be split into other attributes, such as a first name.
• Composite: an attribute that can be split into other attributes, such as name being split into first, middle, and last name.
• Derived: an attribute that is calculated or determined from another attribute, such as the age of record being calculated from the created date.

An attribute can also be single-value or multi-value:

• Single-value: an attribute that is only captured once for
• Multi-Value: an attribute that can be captured more than once for an entity, such as multiple phone numbers.

What is Cardinality?

Cardinality represents the number of instances of an entity that exist in a relationship between two entities. This is often expressed as a number but could also be a symbol, depending on the style of diagram used. Common cardinality values are zero, one, or many.

We’ll see some examples of cardinality later in this guide.

Natural Language

When we are creating an ERD we often have an idea of what we want to capture. This can usually be expressed in words, or using “natural language”.

Some examples are:

• “Record students, courses they enrol in, and teachers who teach the course”
• “Capture the customer orders, customer details, and where the orders are being sent”
• “Capture patient data and the operations they had”

These sentences include a few different types of words, which can be used as a starting point for an ERD. They are represented in a few different ways:

• Noun: a “thing”, such as a student or customer. Represented as an entity.
• Verb: an action, such as enrol or send. Represented as a relationship between two entities.
• Adjective: a describing word, such as residential or advanced. Represented as an attribute on an entity.

This can help you translate a description of what you need to diagram into an actual diagram.

Symbols and notations

When creating an ERD, it can be simple to create boxes and lines between them. But, like many things in software development, there are a few different methods and standards that are available. For ERDs, there are several notation standards, which define the symbols used.

Here’s an example of the symbols used with the Chen notation style.

Here’s an example ERD using Chen notation:

Crow’s Foot

Here’s an example of the symbols used with the Crow’s foot notation style. This is the style you’ll see the most on Database Star as it’s the one I’m most familiar with. It’s called “crow’s foot’ as the symbol for a many relationship looks like the foot of a crow with its three prongs.

Here’s an example ERD using Crow’s Foot notation:

Here’s an example of the symbols used with the Bachman notation style.

Here’s an example ERD using Bachman notation:

Here’s an example of the symbols used with the IDEF1X notation style.

Here’s an example ERD using IDEF1X notation:

Here’s an example of the symbols used with the Barker notation style.

Conceptual, logical, physical

An Entity Relationship Diagram can be drawn at three different levels: conceptual, logical, or physical.

Each of these levels has a different level of detail and are used for a different purpose.

Let’s see some examples.

Conceptual Data Model

The conceptual data model shows the business objects that exist in the system and how they relate to each other.

It defines the entities that exist, which are not necessarily tables. Thinking of tables is too detailed for this type of data model.

An example of a conceptual data model is shown here. It shows students, courses, and how they relate.

Logical Data Model

A logical model is a more detailed version of a conceptual data model. Attributes are added to each entity, and further entities can be added that represent areas to capture data in the system.

Here’s an example of the student and course data model created as a logical data model.

Physical Data Model

The physical data model is the most detailed data model in this process. It defines a set of tables and columns and how they relate to each other. It includes primary and foreign keys, as well as the data types for each column.

These diagrams can be created manually in a data modelling tool. They are also often generated by an IDE from an existing database.

Here’s an example of the student and course physical data model.

This table outlines the differences between a conceptual, logical, and physical model:

How to Create an Entity Relationship Diagram

So how do you create a data model or an Entity Relationship Diagram?

I’ve detailed this in my Relational Database Design course, and I’ve also explained it in my guide to designing a database .

The process to create an ERD is:

• Write a sentence or two about what you are storing data about
• List what you’re storing data about – the nouns/objects
• List the information you want to store for each object
• Describe the relationships between each object
• Draw the diagram

The steps listed here are brief but the process can take some time, depending on how familiar you are with the system and how experienced you are with creating Entity Relationship Diagrams.

Tools to Use

What tool should you use to create a data model or an Entity Relationship Diagram?

There are a lot of applications available to help you create one. I’ve written a post that lists them all with a comparison of major features and price, which you can find here: 79 Data Modeling Tools Compared .

Personally, I use LucidChart as it’s simple to use and web-based. But in the past, I’ve used Visio and even the data modelling capabilities inside an IDE.

That page above includes a range of tools and some recommendations if you’re not sure what to use.

You can also start with a pen and paper to get an understanding of how a diagram can be created. I often start by drawing one in my notebook. It gets messy eventually, but I transfer it to an electronic copy anyway.

Tips for Creating an Entity Relationship Diagram

Here are some tips for creating an Entity Relationship Diagram:

• Determine the right level of detail based on the purpose of the diagram. Development teams often find the logical model the most useful, but others might find the conceptual model more valuable.
• Review the entities and attributes to see if they include everything you want to store in the system.
• Name all entities and attributes.
• If you have a large diagram, consider using colours to highlight different sections, or breaking it up into smaller diagrams.
• Be consistent with your naming and the symbols you use.

An Entity Relationship Diagram is a great tool to help you define, understand, and communicate the requirements of a system. It can be modelled at a high level (conceptual data model), a detailed level (physical data model) or a level in between (logical data model).

There is a range of modelling notations or types of symbols which define how entities, attributes, and relationships are captured.

If you want to get started with creating an ERD for your system, consider drawing one on paper, or use one of the many tools available.

19 thoughts on “A Guide to the Entity Relationship Diagram (ERD)”

Hi, may I congratulate you on a job very well done. Your comparative diagram notation are clear, you don’t use too much jargon. Kudo

Very clearly explained, Thank You

excellent job with the explanation. Thanks, it really helps👍👍

Great insight will be coming can you help me solve my question from my class? To identify a problem of an organization and develop ER-Diagram and a database management system to solve it.

You need to give lecture to our doctor at the university. I am glad that English is the science language not German or any other language,

Very well explained, as I was struggling of what is a ERD, how do I design it. But now you have explained clearly as I understand very much. I like to say thank you for your hard effort.

Nice post!I will read more post in this site! Thank you!

Great article, really clear and well-written -thank you!

Just one minor point; I think the second Bachman diagram should actually be a Barker example?

Dear mister genius, thank you.

The notes are very clear and understandable.

i support you dear.

Thats the best description of data modelling I’ve seen in my quest to understand the concept

Excellent Explain

help me a lots, tyvm

Very understandable 😊

Great job, thank you for explaning so clearly

thank you so mach

this is great content manhz, very simple but detailed explanation init

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How to Draw an ER Diagram

What are your erd needs, i want to make my own erd in lucidchart., i want to make an erd from a lucidchart template..

While ERDs may seem hard, they’re not as tricky as they appear. Entity-relationship diagrams can easily be built with the shapes included in a free Lucidchart account. Follow these steps to begin diagramming!

2 minute read

Want to make an ERD of your own? Try Lucidchart. It's quick, easy, and completely free.

Identify the components

Entity-relationship diagrams are incredibly useful, and you can easily create one of your own by following these simple steps.

1. Determine the entities: Entities are typically nouns such as car, bank, student, or product.

2. Identify the relationships: Relationships highlight how entities interact with each other.

Relationships are typically verbs such as “buys,” “contains,” or “does.” In our example, the relationships “Registers for” and “Teaches” effectively explain the interactions between the three entities.

3. Add attributes: Attributes show specific characteristics of an entity, refining what information is important to the model.

4. Complete the diagram

Organizing the ERD in a logical way is incredibly important to increase comprehension. The main purpose of entity-relationship diagrams is to model a complex database, so learning how to create simple, logical ERDs is key.

How to create an ER Diagram

Enable erd shape libraries.

In a new document, make sure that the entity-relationship shapes libraries are enabled by clicking on the “+ Shapes” button found in the left menu.

Drag and drop shapes

Once you have enabled the entity relationship shapes, add shapes to the canvas by clicking on the desired shape, and dropping it wherever you want it.

Connect shapes

After placing the appropriate shapes on the canvas, connect the shapes by dragging out from the red dots at the borders of the shapes. Then, you can change the line ending in the toolbar above the canvas.

Additional Resources

• What is an Entity Relationship Diagram (ERD)?
• Entity-Relationship Diagram Symbols and Notation

With the help of Lucidchart, creating professional-looking ERDs, data flows, and other specialized diagrams has never been easier. Since all editing takes place right in a web browser, collaborating and sharing is as simple as the press of a button. Sign up for a free account and check it out for yourself.

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Lesson 3 of 9 By Ravikiran A S

Table of Contents

An Entity Relationship Diagram is a diagram that represents relationships among entities in a database. It is commonly known as an ER Diagram. An ER Diagram in DBMS plays a crucial role in designing the database. Today’s business world previews all the requirements demanded by the users in the form of an ER Diagram. Later, it's forwarded to the database administrators to design the database.

What is an ER Diagram?

An Entity Relationship Diagram (ER Diagram) pictorially explains the relationship between entities to be stored in a database. Fundamentally, the ER Diagram is a structural design of the database. It acts as a framework created with specialized symbols for the purpose of defining the relationship between the database entities. ER diagram is created based on three principal components: entities, attributes, and relationships.

The following diagram showcases two entities - Student and Course, and their relationship. The relationship described between student and course is many-to-many, as a course can be opted by several students, and a student can opt for more than one course. Student entity possesses attributes - Stu_Id, Stu_Name & Stu_Age. The course entity has attributes such as Cou_ID & Cou_Name.

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What is an ER Model?

An Entity-Relationship Model represents the structure of the database with the help of a diagram. ER Modelling is a systematic process to design a database as it would require you to analyze all data requirements before implementing your database.

History of ER models

Peter Chen proposed ER Diagrams in 1971 to create a uniform convention that can be used as a conceptual modeling tool. Many models were presented and discussed, but none were suitable. The data structure diagrams offered by Charles Bachman also inspired his model.

Why Use ER Diagrams in DBMS?

• ER Diagram helps you conceptualize the database and lets you know which fields need to be embedded for a particular entity
• ER Diagram gives a better understanding of the information to be stored in a database
• It reduces complexity and allows database designers to build databases quickly
• It helps to describe elements using Entity-Relationship models
• It allows users to get a preview of the logical structure of the database

Symbols Used in ER Diagrams

• Rectangles: This Entity Relationship Diagram symbol represents entity types
• Ellipses: This symbol represents attributes
• Diamonds: This symbol represents relationship types
• Lines: It links attributes to entity types and entity types with other relationship types
• Primary key: Here, it underlines the attributes 
• Double Ellipses: Represents multi-valued attributes

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Components of ER Diagram

You base an ER Diagram on three basic concepts:

Weak Entity

Key attribute, composite attribute, multivalued attribute, derived attribute.

• Relationships
• One-to-One Relationships
• One-to-Many Relationships
• Many-to-One Relationships
• Many-to-Many Relationships

An entity can be either a living or non-living component.

It showcases an entity as a rectangle in an ER diagram.

For example, in a student study course, both the student and the course are entities.

An entity that makes reliance over another entity is called a weak entity

You showcase the weak entity as a double rectangle in ER Diagram.

In the example below, school is a strong entity because it has a primary key attribute - school number. Unlike school, the classroom is a weak entity because it does not have any primary key and the room number here acts only as a discriminator.

An attribute exhibits the properties of an entity. 

You can illustrate an attribute with an oval shape in an ER diagram.

Key attribute uniquely identifies an entity from an entity set.

It underlines the text of a key attribute.

For example: For a student entity, the roll number can uniquely identify a student from a set of students.

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An attribute that is composed of several other attributes is known as a composite attribute.

An oval showcases the composite attribute, and the composite attribute oval is further connected with other ovals.

Some attributes can possess over one value, those attributes are called multivalued attributes.

The double oval shape is used to represent a multivalued attribute.

An attribute that can be derived from other attributes of the entity is known as a derived attribute.

In the ER diagram, the dashed oval represents the derived attribute.

Relationship

The diamond shape showcases a relationship in the ER diagram.

It depicts the relationship between two entities.

In the example below, both the student and the course are entities, and study is the relationship between them. 

One-to-One Relationship

When a single element of an entity is associated with a single element of another entity, it is called a one-to-one relationship.

For example, a student has only one identification card and an identification card is given to one person.

One-to-Many Relationship

When a single element of an entity is associated with more than one element of another entity, it is called a one-to-many relationship

For example, a customer can place many orders, but an order cannot be placed by many customers.

Many-to-One Relationship

When more than one element of an entity is related to a single element of another entity, then it is called a many-to-one relationship.

For example, students have to opt for a single course, but a course can have many students.

Many-to-Many Relationship

When more than one element of an entity is associated with more than one element of another entity, this is called a many-to-many relationship.

For example, you can assign an employee to many projects and a project can have many employees.

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How to Draw an ER Diagram?

Below are some important points to draw ER diagram:

• First, identify all the Entities. Embed all the entities in a rectangle and label them properly.
• Identify relationships between entities and connect them using a diamond in the middle, illustrating the relationship. Do not connect relationships with each other.
• Connect attributes for entities and label them properly.
• Eradicate any redundant entities or relationships.
• Make sure your ER Diagram supports all the data provided to design the database.
• Effectively use colors to highlight key areas in your diagrams.

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ER Diagram in DBMS is widely used to describe the conceptual design of databases. It helps both users and database developers to preview the structure of the database before implementing the database. 

If you have any questions or inputs for our editorial team regarding this “ER Diagram in DBMS” article, do share them with us in the comments section below. Our team will review them and help solve them for you very soon!

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About the Author

Ravikiran A S works with Simplilearn as a Research Analyst. He an enthusiastic geek always in the hunt to learn the latest technologies. He is proficient with Java Programming Language, Big Data, and powerful Big Data Frameworks like Apache Hadoop and Apache Spark.

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ER diagram of Library Management System

ER Diagram is known as Entity-Relationship Diagram, it is used to analyze  the structure of the Database. It shows relationships between entities and their attributes. An ER Model provides a means of communication. 

The Library Management System database keeps track of readers with the following considerations –

• The system keeps track of the staff with a single point authentication system comprising login Id and password.
• Staff maintains the book catalog with its ISBN, Book title, price(in INR), category(novel, general, story), edition, author Number and details.
• A publisher has publisher Id, Year when the book was published, and name of the book.
• Readers are registered with their user_id, email, name (first name, last name), Phone no (multiple entries allowed), communication address. The staff keeps track of readers.
• Readers can return/reserve books that stamps with issue date and return date. If not returned within the prescribed time period, it may have a due date too.
• Staff also generate reports that has readers id, registration no of report, book no and return/issue info.

Follow given link to build a Web application on   Library Management System .

Below is the ER Diagram for Library Management System:

ER Diagram of Library Management System

This Library ER diagram illustrates key information about the Library, including entities such as staff, readers, books, publishers, reports, and authentication system. It allows for understanding the relationships between entities. 

Entities and their Attributes –

• Book Entity : It has authno, isbn number, title, edition, category, price. ISBN is the Primary Key for Book Entity.
• Reader Entity : It has UserId, Email, address, phone no, name. Name is composite attribute of firstname and lastname. Phone no is multi valued attribute. UserId is the Primary Key for Readers entity.
• Publisher Entity : It has PublisherId, Year of publication, name. PublisherID is the Primary Key.
• Authentication System Entity : It has LoginId and password with LoginID as Primary Key.
• Reports Entity : It has UserId, Reg_no, Book_no, Issue/Return date. Reg_no is the Primary Key of reports entity.
• Staff Entity : It has name and staff_id with staff_id as Primary Key.
• Reserve/Return Relationship Set : It has three attributes: Reserve date, Due date, Return date.

Relationships between Entities – 

• A reader can reserve N books but one book can be reserved by only one reader. The relationship 1:N.
• A publisher can publish many books but a book is published by only one publisher. The relationship 1:N.
• Staff keeps track of readers. The relationship is M:N.
• Staff maintains multiple reports. The relationship 1:N.
• Staff maintains multiple Books. The relationship 1:N.
• Authentication system provides login to multiple staffs. The relation is 1:N.

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