An entity-relationship diagram (ERD) is a graphical representation of an organization’s data. An ERD can be used to represent any kind of data, including:
-The contents of a database
-The relationships between people, objects, or ideas
-The processes that transform data
Building an ERD is the first step in designing a database. It allows you to see how the different elements of your data fit together, and to identify any potential problems with your design.
What is an Entity Relationship Diagram (ERD)?
An Entity Relationship Diagram (ERD) is a data modeling technique that graphically illustrates an information system’s entities and the relationships between those entities. An ERD is a conceptual and representational model of data used to describe a database.
Entity Relationship Diagrams are a major data modeling tool and will help organize the data requirements for any project into an understandable format. When complete, ERDs can provide a graphical view of tables, views, stored procedures and relationships between them. They are also known as ER diagrams or ERD diagrams.
There are three basic elements in an ERD:
Entities are the “things” about which we want to store information. For example, in a school database we might want to store information about students, classes, and instructors. In this case, “student,” “class,” and “instructor” would be considered entities. Attributes are the pieces of information that describe an entity. For example, some of the attributes of the entity “student” might be “student ID,” “name,” and “address.” In addition to being able to store information about entities, we also need to be able to define relationships between those entities; this is where relationships come in. Relationships allow us to answer questions such as: “What classes is a particular student taking?” or “Who teaches this class?”
In order for an Entity Relationship Diagram to be effective it must follow certain conventions:
- Entities must be nouns (e.g., student not students).
- Attributes must be single words that describe the entity (e.g., name not first name).
- Relationships must be verbs (e.g., takes not course).
The first step in building an ERD is to
The first step in building an ERD is to identify the entities that will be included in the diagram. An entity is any object, person, place, or thing that can be uniquely identified. Once you have identified the entities, you will need to decide on the relationships between them. Relationships can be one-to-one, one-to-many, or many-to-many.
How to create an ERD
There are a few different methods you can use to create your ERD, but the most common is the top-down approach.
- Start by identifying the main entities (or objects) in your system. These are typically the nouns in your requirements document.
- For each entity, identify its attributes. Attributes are the properties or characteristics of an entity. They can be physical (size, weight, color) or non-physical (name, description).
- Once you have a list of entities and attributes, you can start to identify relationships between them. Relationships are typically verbs that connect two entities together (e.g., “employee works for company”).
- Finally, you can add any additional information that might be relevant to your diagram, such as cardinality or primary keys.
What are the benefits of using an ERD?
Entity Relationship Diagrams (ERD) are a graphical representation of data that depicts how data is related to entities and attributes. An ERD can be used to model Data Warehouse schemas, relational database schemas, and business process models.
There are many benefits of using an ERD when modeling data, including:
- improved communication between designers and stakeholders;
- enhanced understanding of the domain;
- identification of opportunities for data reuse;
- prevention of redundant data;
- better adherence to design standards; and
- improved development efficiency.
After you have identified the main entities in your system, you need to decide how they are related to each other. This is where you start to draw lines between the boxes on your diagram. The relationships can be one-to-one, one-to-many, or many-to-many.
One-to-one relationships are when each instance of one entity can only be related to one instance of another entity. For example, each person has only one social security number. One-to-many relationships are when each instance of one entity can be related to multiple instances of another entity. For example, each person can have multiple addresses. Many-to-many relationships are when multiple instances of one entity can be related to multiple instances of another entity. For example, a product can be purchase by many customers and a customer can purchase many products.
Once you have determined the relationships between your entities, you need to give them names. These names will become the key terms in your database tables. In a one-to-one relationship, you would name the relationship after the entity that it is related to. In a one-to-many relationship, you would name the relationship after the entity that it is relate