- What is an Entity Relationship Diagram?<\/a><\/li>
- Components of ER Diagrams<\/a>
- Entities<\/a><\/li>
- Attributes<\/a><\/li>
- Relationships<\/a><\/li><\/ul><\/li>
- Type of ERD models<\/a>
- 1. Conceptual data model<\/a><\/li>
- 2. Logical data model<\/a><\/li>
- 3. Physical data models<\/a><\/li><\/ul><\/li>
- ER Diagram Notations<\/a>
- 1. Chen notation style<\/a><\/li>
- 2. Crow’s foot\/Martin\/information engineering style<\/a><\/li>
- 3. Bachman notation<\/a><\/li>
- 4. IDEF1X notation<\/a><\/li>
- 5. Barker style<\/a><\/li><\/ul><\/li>
- ER Diagram Examples<\/a>
- 1. Flow chart<\/a><\/li>
- 2. Process map<\/a><\/li>
- 3. Data flow diagram<\/a><\/li>
- 4. UML class diagram<\/a><\/li>
- 5. Network diagram<\/a><\/li>
- 6. Database file reference<\/a><\/li><\/ul><\/li>
- How to Create an ER Diagram<\/a>
- 1. Choose the tools for creating ER diagrams<\/a><\/li>
- 2. Bring together the elements<\/a><\/li>
- 3. Use a template<\/a><\/li>
- 4. Integrate all relevant data<\/a><\/li><\/ul><\/li>
- Uses and Applications of ER Diagrams<\/a>
- 1. Database design<\/a><\/li>
- 2. Process design<\/a><\/li>
- 3. Quality control<\/a><\/li>
- 4. Documentation<\/a><\/li><\/ul><\/li>
- Limitations and Challenges of ER Diagrams<\/a><\/li>
- Tips and Resources for ER Diagram Creation<\/a>
- Choose your level first<\/a><\/li>
- Follow a naming convention<\/a><\/li>
- Throw in some color<\/a><\/li>
- Add notes<\/a><\/li>
- Set up version control<\/a><\/li><\/ul><\/li><\/ul>\n\t\t\t<\/div>\n\t\t<\/div><\/div>\n\n\n
What is an Entity Relationship Diagram?<\/strong><\/h2>\n\n\n\n
An entity relationship diagram (ERD) is a visual representation of interrelated items within a specific domain of knowledge. Designed by computer scientist and Carnegie-Mellon professor Peter Chen in the 1970s, the entity relationship model uses a set of symbols to represent the interconnectedness of various entities.<\/p>\n\n\n\n
A typical ERD comprises of two things:<\/p>\n\n\n\n
- \n
- Entities<\/strong>: People, objects, concepts, locations, or assets represented as boxes<\/li>\n\n\n\n
- Relationships<\/strong>: Connections between entities, drawn as lines<\/li>\n<\/ul>\n\n\n
\n![\"entity](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-12.png\")
Simple example of an entity relationship diagram (Source: <\/em>Peter Chen<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n In theory, you can use the entity relationship diagram to visualize anything. For instance, you might create an organizational hierarchy<\/a> as an ERD. However, in practice, it is most commonly used in designing relational databases in software, where the following components are critical.<\/p>\n\n\n\n
Components of ER Diagrams<\/strong><\/h2>\n\n\n\n
A typical ER diagram only has two components, i.e., entities and relationships. However, the nature of these might vary, creating more components. Let\u2019s look at them all.<\/p>\n\n\n
\n![\"entity](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-13.png\")
Example of an entity relationship diagram with various components (Source: <\/em>Wikimedia Commons<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n Entities<\/h3>\n\n\n\n
Entities are definable items such as person, object, event, location, etc. They exist independently, have a unique identifier, and the information stored is about them. They are typically represented as rectangles.<\/p>\n\n\n
\nFor example, if you\u2019re building an e-commerce website, each product, customer, or order is an entity.<\/p>\n\n\n<\/div>\n\n\n
Entity types<\/strong>: Entities are grouped into types, such as products, customers, or vendors. Each of these types will have multiple entities under them.<\/p>\n\n\n\n
Entity categories<\/strong>: Within each entity type, you might have categories. Electronics, pet food, stationery, etc. are categories under products. <\/p>\n\n\n\n
Strong vs. weak entities<\/strong>: Strong entities are independent ones with enough information about them available. Weak entities are those that occur as a consequence of another entity. In the e-commerce example, an order would be a strong entity. However, the discount applicable to that order would be a weak entity.<\/p>\n\n\n\n
Associative entities<\/strong>: An associative entity is a link between two entities with its own data.<\/p>\n\n\n
\nFor instance, the cart might be an associative entity between shopping and checkout.<\/p>\n\n\n<\/div>\n\n\n
Attributes<\/h3>\n\n\n\n
Attributes are data points or properties related to an entity, depicted as ovals or circles. Attributes can be simple, composite, derived, or multivalue.<\/p>\n\n\n
\n- \n
- Simple attributes<\/strong>: A singular piece of simple information that can not be further broken down. E.g.: Order date<\/li>\n\n\n\n
- Composite attributes<\/strong>: A collection of attributes to form coherent data. E.g., Address as a collection of door number, street name, city, and pin code<\/li>\n\n\n\n
- Derivative attributes<\/strong>: Calculated based on existing information or other attributes. E.g., Cart value<\/li>\n\n\n\n
- Multivalue attributes<\/strong>: Multiple values per entity. E.g.: Several delivery addresses<\/li>\n<\/ul>\n\n\n<\/div>\n\n\n
Each of these attributes also has a primary and foreign key that defines them. Order number, product ID, customer mobile number, etc. can be keys. <\/p>\n\n\n\n
Relationships<\/h3>\n\n\n\n
Relationships are the connections between entities in the diagram. It shows how they are related to one another, usually within a rhombus. There are primarily three types of relationships.<\/p>\n\n\n\n
One-to-one<\/strong>: A direct relationship between records in one entity to another. For example, the product ID is connected to its corresponding price.<\/p>\n\n\n\n
One to many<\/strong>: Relationships between one record in one entity and multiple records in another. For example, a product might have multiple size variants.<\/p>\n\n\n\n
Many to many<\/strong>: Relationships between multiple records in two entities. For example, tiered shipping costs applicable to multiple products.<\/p>\n\n\n\n
Depending on the type of ERD model you need, the components you use might vary. Here\u2019s how.<\/p>\n\n\n\n
Type of ERD models<\/strong><\/h2>\n\n\n\n
The type of an entity relationship diagram depends on the level of detail or abstraction it visualizes. Typically, this falls under three categories.<\/p>\n\n\n\n
1. Conceptual data model<\/h3>\n\n\n\n
A conceptual data model is the highest level containing minimum detail. It references master data entities across the organization. Teams use conceptual data models to define the data architecture of the company, support model integration, and set the foundation for smaller logical models.<\/p>\n\n\n\n
2. Logical data model<\/h3>\n\n\n\n
The logical data model includes more detail than the conceptual model, including operational and transactional entities. It is used to design small-scale data projects within the organization. <\/p>\n\n\n\n
3. Physical data models<\/h3>\n\n\n\n
A physical data model is the blueprint for the database structure. It includes granular details, such as attributes, primary keys, foreign keys, cardinality, etc. They are derived from logical or conceptual models developed by business analysts.<\/p>\n\n\n\n
Irrespective of the type of model, all ERDs use rectangles, ovals, rhombus (diamond shapes), and lines; notations can vary based on the style you\u2019re using. Let\u2019s understand them in detail.<\/p>\n\n\n\n
ER Diagram Notations<\/strong><\/h2>\n\n\n\n
Since Chen\u2019s recommendation many moons ago, multiple notions have emerged and evolved. Here are a few commonly used ones.<\/p>\n\n\n\n
1. Chen notation style<\/h3>\n\n\n\n
The original style recommended by Peter Chen still holds ground as a widely used framework. In this notation, the following shapes are used.<\/p>\n\n\n
\n- \n
- Rectangle<\/strong>: Entity<\/li>\n\n\n\n
- Rectangle with a double line border<\/strong>: Weak entity<\/li>\n\n\n\n
- Rectangle with a rhombus inside<\/strong>: Associative entity<\/li>\n\n\n\n
- Oval<\/strong>: Attribute<\/li>\n\n\n\n
- Oval with double line border<\/strong>: Multivalue attribute<\/li>\n\n\n\n
- Oval with dotted line border<\/strong>: Derived attribute<\/li>\n\n\n\n
- Rhombus<\/strong>: Relationship<\/li>\n\n\n\n
- Rhombus with double line border<\/strong>: Weak relationship<\/li>\n\n\n\n
- Straight line<\/strong>: Mandatory relationship<\/li>\n\n\n\n
- Dotted line<\/strong>: Optional relationship<\/li>\n\n\n\n
- Characters 1, N, M<\/strong>: Cardinality of one-to-one, one-to-many, and many-to-many relationships<\/li>\n<\/ul>\n\n\n<\/div>\n\n\n
2. Crow’s foot\/Martin\/information engineering style<\/h3>\n\n\n\n
Similar to Chen\u2019s notation, the crow\u2019s foot style represents entities and relationships as boxes and lines. It differs by adding different shapes at the end of the lines for the cardinality of the relationship.<\/p>\n\n\n
\n![\"Example](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-14.png\")
Example of crow\u2019s feet notation (Source: <\/em>Wikimedia Commons<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n The shapes used are ring (meaning zero), dash (one), and crow\u2019s foot (many). Users combine these shapes to express the cardinality of the relationship. <\/p>\n\n\n
\nFor example, two dashes mean minimum one, maximum one. Dash and crow\u2019s feet mean minimum one and maximum infinite.<\/p>\n\n\n<\/div>\n\n\n
3. Bachman notation<\/h3>\n\n\n\n
The Bachman style, a commonly used data structure diagram, uses rectangles to represent a relation (collection of attributes) and lines for connections. The end of each line has one arrow to indicate a one-to-one relationship or two arrows for a one-to-many relationship. <\/p>\n\n\n
\n![\"Bachman](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-15.png\")
Bachman notation (Source: <\/em>Wikipedia Commons<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n 4. IDEF1X notation<\/h3>\n\n\n\n
Integration DEFinition for information modeling (IDEF1X) uses rectangles for independent entities and rounded rectangles for dependent entities. Domains are set in ovals. <\/p>\n\n\n\n
Relationships are represented through lines; however, the end of a line with a circle and letters indicates cardinality.<\/p>\n\n\n
\n![\"Relationship](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-16.png\")
Relationship cardinality syntax in IDEF1X notation (Source: <\/em>Wikimedia Commons<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n 5. Barker style<\/h3>\n\n\n\n
Barker\u2019s style is an adaptation of the crow\u2019s feet model popularized when the creator joined Oracle and integrated it into its CASE modeling tools. This notation uses the following symbols:<\/p>\n\n\n
\n- \n
- Straight line<\/strong>: Mandatory relationship (one-to-one)<\/li>\n\n\n\n
- Dotted line<\/strong>: Optional relationship<\/li>\n\n\n\n
- Crow\u2019s feet<\/strong>: One-to-many, many-to-one or many-to-many relationships<\/li>\n<\/ul>\n\n\n<\/div>\n\n\n
With these in mind, let\u2019s look at a few examples.<\/p>\n\n\n\n
ER Diagram Examples<\/strong><\/h2>\n\n\n\n
An entity relationship diagram can be as simple as a visual representation of a marriage or as complex as an enterprise\u2019s data architecture. Here\u2019s a cross-section of diagram examples<\/a> to get a better idea.<\/p>\n\n\n\n
1. Flow chart<\/h3>\n\n\n\n
A flow chart is the simplest form of entity relationship diagram. It connects various elements (entities) to visualize a logical decision-making flow. The following diagram asks a series of questions to decide whether an organism is an autotroph or heterotroph.<\/p>\n\n\n
\n![\"Flow](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-17.png\")
Is it an autotroph, heterotroph, or a subtype? (Source: <\/em>Wikimedia Commons<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n 2. Process map<\/h3>\n\n\n\n
A process map<\/a> is a visual representation of the journey, events, and milestones in any process. It maps who needs to do what at every step of the way. The following workflow diagram example<\/a> demonstrates the process of writing for English Wikipedia.<\/p>\n\n\n
\n![\"Article](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-18-1011x1400.png\")
Article creation workflow (Source: <\/em>Wikimedia Commons<\/em><\/a>)<\/em><\/figcaption><\/figure><\/div>\n\n\n If you\u2019re new to flow charts and process maps, try ClickUp\u2019s Process Flow Chart Template<\/a>. This beginner-friendly, customizable template allows you to graphically represent any process within your organization, complete with pre-designed shapes, lines, and a legend.<\/p>\n\n\n\n
- Dotted line<\/strong>: Optional relationship<\/li>\n\n\n\n
- Rectangle with a double line border<\/strong>: Weak entity<\/li>\n\n\n\n
- Composite attributes<\/strong>: A collection of attributes to form coherent data. E.g., Address as a collection of door number, street name, city, and pin code<\/li>\n\n\n\n
- Relationships<\/strong>: Connections between entities, drawn as lines<\/li>\n<\/ul>\n\n\n
- Follow a naming convention<\/a><\/li>
- 2. Process design<\/a><\/li>
- 2. Bring together the elements<\/a><\/li>
- 2. Process map<\/a><\/li>
- 2. Crow’s foot\/Martin\/information engineering style<\/a><\/li>
- 2. Logical data model<\/a><\/li>
- Attributes<\/a><\/li>
- Components of ER Diagrams<\/a>
![\"ClickUp's](\"https:\/\/clickup.com\/blog\/wp-content\/uploads\/2025\/01\/image-20.png\")