What is The ER(Entity Relationship) Schema Diagram ✨
In this article, I plan to provide you with valuable information about the ER (Entity Relationship) Schema diagram. In terms of content, I paid great attention to including definitions, examples and visuals to help you understand this concept better. I hope it will be a useful and instructive article for all of you. Happy reading to all of you. 📖
TOPICS:
— What is an Entity Relationship Schema Diagram ?
— Why Make an ER Schema Diagram?
— The History of Entity RelationShip Schema Diagrams
— Common Entity RelationShip Symbols
— Entity RelationShip Schema Diagram Models
— RelationShip
— Attributes
— How to Draw an ER Diagram
— Creating Entity RelationShip Schema Diagram With DatabaseSample
— Creating Entity RelationShip Schema Diagram With AI Database Generator
What is an Entity Relationship Schema Diagram ?
Entity Relationship Schema Diagram stands for entity relationship diagram. People also call these types of diagrams ER diagrams and Entity Relationship Models. An Entity Relationship Schema Diagram visualizes the relationships between entities like people, things, or concepts in a database. An Entity Relationship Schema Diagram will also often visualize the attributes of these entities.
By defining the entities, their attributes, and showing the relationships between them, an ER diagram can illustrate the logical structure of databases. This is useful for engineers hoping to either document a database as it exists or sketch out a design of a new database.
Why Make an ER Schema Diagram?
An ER diagram can help businesses document existing databases and thereby troubleshoot logic or deployment problems or spot inefficiencies and help improve processes when a business wants to undertake business process re-engineering. ERDs can also be used to design and model new databases and make sure that engineers can identify any logic or design flaws before they’re implemented in production.
- Document an existing database structure
- Debug, troubleshoot, and analyze
- Design a new database
- Gather design requirements
- Business process re-engineering (BPR)
When documenting a system or process, looking at the system in multiple ways increases the understanding of that system. ERD diagrams are commonly used in conjunction with a data flow diagram to display the contents of a data store. They help us to visualize how data is connected in a general way, and are particularly useful for constructing a relational database.
The History of Entity Relationship Schema Diagrams
Peter Chen developed ERDs in the 1970s and published his proposal for entity relationship modeling in a 1976 paper titled “The Entity-Relationship Model: Toward a Unified View of Data”. Peter Chen was a computer scientist who worked on improving database design. His entity relationship model was a way to visualize a database that unified other existing models into a single understanding that removed ambiguities. Prior to ERDs, there were three data models for databases: the network model, the relational model, and the entity set model. Each had their own strengths and weaknesses, but none provided a complete view of the database. With an ERD, Chen could provide a unified framework for database modeling.
Peter Chen’s work was greatly influenced by scientists and engineers who came before him, specifically Charles Bachman, who worked on visualizing databases in the 1960s and his data structure diagrams became known as Bachman diagrams.
Chen’s entity relationship model is in many ways the foundation for later practices like Unified Modeling Language or UML in information systems.
In the 1980s, another computer scientist named James Martin, worked to further refine Chen’s ER model and introduced what’s known today as the IE notation. IE notation uses Crow’s foot to express cardinality (one to many relationship) instead of Chen’s notation to epxress the same.
Common Entity RelationShip Symbols
An ER diagram has three main components: entities, relationships, and attributes connected by lines.
- Entities, which are represented by rectangles. An entity is an object or concept about which you want to store information. A weak entity is an entity that must be defined by a foreign key relationship with another entity as it cannot be uniquely identified by its own attributes alone.
- Relationships, which are represented by diamond shapes, show how two entities share information in the database. In some cases, entities can be self-linked.
- Attributes, which are represented by ovals. A key attribute is the unique, distinguishing characteristic of the entity. For example, an employee’s social security number might be the employee’s key attribute.
A multivalued attribute can have more than one value. For example, an employee entity can have multiple skill values. A derived attribute is based on another attribute. For example, an employee’s monthly salary is based on the employee’s annual salary. - Connecting lines, solid lines that connect attributes and show the relationships of entities in the diagram.
- Cardinality specifies the numerical attribute of the relationship between entities. It can be one-to-one, many-to-one, or many-to-many.
ERD Models
Entity Relationship Models can also vary based on the level of abstraction visualized. There are usually three models people refer to based on the level of detail you want to show: conceptual ERD, logical ERD, and physical ERD.
- Conceptual ERD or data model: This model has the most abstraction and least amount of detail, as such it’s appropriate for large projects that need a higher level view used by business analysts. A typical conceptual ERD will contain entities and relationships, but offer no details on specific database columns or cardinalities. It’s a general, high-level view of database design.
- Logical ERD or data model: This model adds more detail to the conceptual model by defining additional entities that are operational and transactional.
- Physical ERD or data model: This model serves as the actual design or blueprint of the database with lots of technical details including defining cardinality and showing primary and foreign keys of entities instead of just their abstract semantic names. For this type of ERD, attributes will often be listed to represent the columns of the real database table.
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.
Attribute
An attribute exhibits the properties of an entity.You can illustrate an attribute with an oval shape in an ER diagram.
Key Attribute
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.
Composite Attribute
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.
Multivalued Attribute
Some attributes can possess over one value, those attributes are called multivalued attributes. The double oval shape is used to represent a multivalued attribute.
Derived 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.
How to Draw an ER Diagram?
1-Below are some important points to draw ER diagram:
2-First, identify all the Entities. Embed all the entities in a rectangle and label them properly.
3-Identify relationships between entities and connect them using a diamond in the middle, illustrating the relationship. Do not connect relationships with each other.
4-Connect attributes for entities and label them properly.
5-Eradicate any redundant entities or relationships.
6-Make sure your ER Diagram supports all the data provided to design the database.
7-Effectively use colors to highlight key areas in your diagrams.
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