How to Create an Entity Relationship Diagram (ERD)

An Entity Relationship Diagram (ERD) is a data model describing how entities (or concepts or things) relate to one another. When created by business analysts, ERDs can be used to understand the business domain, clarify business terminology, and connect business concepts to database structures.

Essentially, a conceptual or logical ERD will visually show how the terms in your glossary relate to one another. They are especially helpful in clarifying information models for relational databases and helping business users understand database structures at a high level and without details.

(This might surprise you as typically ERDs look almost ridiculously complicated. That’s because most ERDs are automated output from physical database designs, not carefully crafted abstractions of business concepts.)

For now, onto what goes into an Entity Relationship Diagram.

(By the way, we cover ERDs in more detail in Data Modeling for Business Analysts – a virtual class covering the most critical data modeling techniques you need to know.)

The Key Elements of an ERD

Although they look complex, an ERD has 3 simple components.

  • Entities – An entity is a thing. In business domain terms, it’s a concept or glossary-level term. In relational database terms, it’s the table.
  • Relationships – The real insight from this type of diagram comes when we see how entities relate to one another, or relationships. Relationships can be thought of as verbs that link two or more nouns. Relationships can be modeled numerically, using the multiplicity syntax from a class diagram, or using Crows Foot Notation.
  • Attributes – Within each entity, there can be more than one attribute. Attributes provide detailed information about the concept. In a relational database, attributes are represented by the fields where the information inside a record is held.

An ERD Sample

Now, let’s see how all these components work together. Here’s a sample ERD from the materials for our Data Modeling for Business Analysts course. The relationships are modeled using Crows Foot Notation.

ERD-Crows-Foot

Steps to Creating an ERD

Like any analysis model, creating an ERD is an iterative process that involves elicitation, analysis, and review with stakeholders. Here are some steps you’ll go through as you create an ERD.

  1. Create boxes for each entity or primary business concept relevant to your model.
  2. Model the relationships between each by drawing lines to connect related entities. Label the relationships using verbs or a numeric notation. Crows Foot Notation is common for ERDs, but you can also use the multiplicity notation from UML’s Class Diagrams.
  3. Identify relevant attributes within each entity. For a conceptual model, focus on the most important attributes. As your model evolves, make your attribute lists more specific.
  4. Review your model with business and technical stakeholders.
  5. Repeat until your domain is well-represented by your model.

As an end result, you’ll have clearly defined how different business concepts relate to one another, and created a solid conceptual foundation for designing a relational database to support your business requirements, as well as a way to get business and technical stakeholders on the same page about how these concepts relate.

>>Learn More About Data Modeling

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