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The first law of ecology and environmental science is: Everything is connected to everything else. In many ways, this is true of business systems as well.
People are connected to each other as team members, managers, support staff, etc. Each team member’s data, such as name, email, social security number, compensation package, etc. is connected to their profile. In modern software, microservices are interconnected.
Effectively managing these connections requires a visual and comprehensive modeling—a framework called the entity relationship diagram.
In this blog post, we see what it is, how it works, and how you can use entity relationship diagrams in your everyday work.
What is an Entity Relationship Diagram?
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.
A typical ERD comprises of two things:
- Entities: People, objects, concepts, locations, or assets represented as boxes
- Relationships: Connections between entities, drawn as lines
In theory, you can use the entity relationship diagram to visualize anything. For instance, you might create an organizational hierarchy as an ERD. However, in practice, it is most commonly used in designing relational databases in software, where the following components are critical.
Components of ER Diagrams
A typical ER diagram only has two components, i.e., entities and relationships. However, the nature of these might vary, creating more components. Let’s look at them all.
Entities
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.
For example, if you’re building an e-commerce website, each product, customer, or order is an entity.
Entity types: Entities are grouped into types, such as products, customers, or vendors. Each of these types will have multiple entities under them.
Entity categories: Within each entity type, you might have categories. Electronics, pet food, stationery, etc. are categories under products.
Strong vs. weak entities: 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.
Associative entities: An associative entity is a link between two entities with its own data.
For instance, the cart might be an associative entity between shopping and checkout.
Attributes
Attributes are data points or properties related to an entity, depicted as ovals or circles. Attributes can be simple, composite, derived, or multivalue.
- Simple attributes: A singular piece of simple information that can not be further broken down. E.g.: Order date
- Composite attributes: A collection of attributes to form coherent data. E.g., Address as a collection of door number, street name, city, and pin code
- Derivative attributes: Calculated based on existing information or other attributes. E.g., Cart value
- Multivalue attributes: Multiple values per entity. E.g.: Several delivery addresses
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.
Relationships
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.
One-to-one: A direct relationship between records in one entity to another. For example, the product ID is connected to its corresponding price.
One to many: Relationships between one record in one entity and multiple records in another. For example, a product might have multiple size variants.
Many to many: Relationships between multiple records in two entities. For example, tiered shipping costs applicable to multiple products.
Depending on the type of ERD model you need, the components you use might vary. Here’s how.
Type of ERD models
The type of an entity relationship diagram depends on the level of detail or abstraction it visualizes. Typically, this falls under three categories.
Conceptual data model
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.
Logical data model
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.
Physical data models
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.
Irrespective of the type of model, all ERDs use rectangles, ovals, rhombus (diamond shapes), and lines; notations can vary based on the style you’re using. Let’s understand them in detail.
ER Diagram Notations
Since Chen’s recommendation many moons ago, multiple notions have emerged and evolved. Here are a few commonly used ones.
Chen notation style
The original style recommended by Peter Chen still holds ground as a widely used framework. In this notation, the following shapes are used.
- Rectangle: Entity
- Rectangle with a double line border: Weak entity
- Rectangle with a rhombus inside: Associative entity
- Oval: Attribute
- Oval with double line border: Multivalue attribute
- Oval with dotted line border: Derived attribute
- Rhombus: Relationship
- Rhombus with double line border: Weak relationship
- Straight line: Mandatory relationship
- Dotted line: Optional relationship
- Characters 1, N, M: Cardinality of one-to-one, one-to-many, and many-to-many relationships
Crow’s foot/Martin/information engineering style
Similar to Chen’s notation, the crow’s 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.
The shapes used are ring (meaning zero), dash (one), and crow’s foot (many). Users combine these shapes to express the cardinality of the relationship.
For example, two dashes mean minimum one, maximum one. Dash and crow’s feet mean minimum one and maximum infinite.
Bachman notation
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.
IDEF1X notation
Integration DEFinition for information modeling (IDEF1X) uses rectangles for independent entities and rounded rectangles for dependent entities. Domains are set in ovals.
Relationships are represented through lines; however, the end of a line with a circle and letters indicates cardinality.
Barker style
Barker’s style is an adaptation of the crow’s feet model popularized when the creator joined Oracle and integrated it into its CASE modeling tools. This notation uses the following symbols:
- Straight line: Mandatory relationship (one-to-one)
- Dotted line: Optional relationship
- Crow’s feet: One-to-many, many-to-one or many-to-many relationships
With these in mind, let’s look at a few examples.
ER Diagram Examples
An entity relationship diagram can be as simple as a visual representation of a marriage or as complex as an enterprise’s data architecture. Here’s a cross-section of diagram examples to get a better idea.
1. Flow chart
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.
2. Process map
A process map 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 demonstrates the process of writing for English Wikipedia.
If you’re new to flow charts and process maps, try ClickUp’s Process Flow Chart Template. This beginner-friendly, customizable template allows you to graphically represent any process within your organization, complete with pre-designed shapes, lines, and a legend.
Bonus: More context diagram templates
3. Data flow diagram
A data flow diagram shows the movement of information through any process or system. It helps data and engineering teams view how data is shared between various entities so they can identify loopholes, if any.
Replicate this simple, yet powerful visual with ClickUp’s Data Flow Diagram Template. Use this ClickUp Whiteboards template to point out data sources and destinations, track entities, and troubleshoot errors/issues.
Bonus: More data flow diagram templates
4. UML class diagram
Unified Modeling Language class diagram is a visual representation of the structure and relationships of classes in object-oriented systems. It typically contains:
- Classes: A blueprint or a framework for an object
- Attributes: Properties of objects
- Operations/methods: Services provided by the classes
- Relationships: Connections, such as association, inheritance, dependency, etc.
There are purpose-designed UML diagram software available. However, for a quick and easy way to draw these visuals, try some UML diagram templates. In particular, ClickUp’s Class Diagram Template enables you to organize classes into logical groups, map relationships, and collaboratively improve their accuracy and effectiveness.
What’s more? You can link it to your ClickUp Tasks for easy access later on.
5. Network diagram
A network diagram is an ERD of computers and telecommunications equipment, such as modems, routers, firewall, cloud storage, etc. The following diagram shows a wireless mesh network connected upstream via a VSAT link.
Create your own map with ClickUp’s Project Network Diagram Template. This template comes pre-loaded with basic shapes for computers, printers, telephones, firewall, routers, and other entities on a network diagram. Drag, drop, and move around these elements to customize them for your needs.
6. Database file reference
A database file reference ERD is a simple visual mapping of the part of the database schema that deals with files in the system. The following example illustrates how that works in WordPress.
Now that you’ve seen some examples, it’s time to draw your own. Let’s see how.
How to Create an ER Diagram
All you need for an ER diagram is a pen and paper or a whiteboard and marker. However, more advanced tools can make it easier and quicker to draw entity relationship diagrams. So, begin there.
1. Choose the tools for creating ER diagrams
There are a number of ERD tools that you can use, such as:
Productivity tools: Spreadsheets, presentation software, and documents are great if you need a simple way to draw shapes and add text. They are easily shareable and accessible. However, they are limited in their features and flexibility.
Design tools: Photoshop, Figma, or Canva are immensely flexible and give you near-unlimited control over your design. On the other hand, they might be difficult to use for non-design teams.
Diagramming tools: Draw.io, Microsoft Visio, or Lucidchart are perfect for drawing ERDs. They come packed with features that support various shapes, notations, etc. However, they might exist in a silo, unable to be connected to projects and tasks.
Customizable whiteboards: Comprehensive project management tools with whiteboards like ClickUp enable you to collaboratively draw diagrams and connect them to everyday work effortlessly.
Here’s how you can use ClickUp to draw and use your ERDs.
2. Bring together the elements
Once you’ve chosen your tool, bring together all the elements included in your ERD. At this stage, also define the purpose of your ERD. Outline why and for whom you’re creating the diagram.
Then, draw shapes for entities and their attributes. Connect them using lines and other notations. On ClickUp Whiteboards, you can insert shapes, add sticky notes, include images, and write text! If all that isn’t enough, you can also hand-draw custom shapes onto your whiteboard for good measure.
3. Use a template
If adding all the elements one by one seems tedious, don’t sweat. Choose from the many free, customizable ERD templates that ClickUp has to offer.
Try ClickUp’s Entity Relationship Diagram Template for a structure to create your relational database. Visualize complex data structures with simple drag, drop, and edit of elements—the no-code way.
Customize the shapes, connectors, fonts, colors, and everything you need to make this ERD your own. Securely share it with key stakeholders for feedback and comments. Keep it updated as your entity relationships evolve.
4. Integrate all relevant data
Once you have the diagram ready, make sure you integrate all the relevant data into it. For example, if you have documentation about the entities on ClickUp Docs or an Excel database, link them. If the ERD is relevant to specific tasks, link them too.
You can also integrate chats into your whiteboard to have asynchronous conversations and contextual collaboration.
Once you’ve created a fabulous ERD, it’s time to use it. Shall we?
Uses and Applications of ER Diagrams
As Peter Chen suggests, you can map any relationship with an ER diagram—even a domestic one. However, some of the most common applications of the entity relationship diagram are in software engineering.
Database design
For software teams, ERDs are important database design tools used for modeling relational databases that visualize the business logic. They add all the entities and relationships to create a holistic view of the database.
Process design
Several organizational workflows use ERDs as the basic framework. It helps map every step in a business or technological process, marking dependencies, connections, boundaries, and pathways.
Quality control
Entity relationship diagrams accelerate troubleshooting by giving a clear and comprehensive view of the entire landscape. It makes it easier to trace bugs back to their root cause.
Documentation
ERDs also are a way of archiving the system design. They are a visual, accessible, and adaptable form in which large amounts of information can be stored, referenced, used, and updated.
Despite its many benefits, ERDs aren’t perfect for every need.
Limitations and Challenges of ER Diagrams
Entity relationship diagrams are specific visuals designed for a narrow purpose. This means that they have their limitations as well.
Restricted to relational data: As the purpose of an ER diagram is to show relationships, it is useless when the data doesn’t have a relational structure.
Limited to structured data: Suitable for relational databases, the ER diagram is not applicable to unstructured or semi-structured data.
Complex symbols: Between crow’s feet and Bachman and IDEF1X, there are various notation formats, which can become confusing if everyone isn’t using the same style.
Missing cardinalities: The lines can give the impression that all of them are one-to-one relationships, which is rarely the case.
When used correctly, these challenges can be easily overcome.
Tips and Resources for ER Diagram Creation
Before we sign off, here are some best practices you can use while creating and using your ERDs.
Choose your level first
Before you draw your diagram, decide if you want it to be at the conceptual, logical, or physical level. This will save a lot of trouble in making decisions around the level of granularity of information.
Follow a naming convention
Make sure the names of entities and attributes are consistent. For instance, use all singular, such as customer, vendor, logistics partner, and delivery person. Use the same spelling for every recurrence.
Throw in some color
Don’t shy away from color coding. You might make the unused tables red or derived attributes purple for easier reading.
Add notes
You don’t need to say everything in the diagram. For explanations, use ClickUp Docs and write down your notes. Link this doc back to your diagram so everyone has easy access. In fact, creating a document with your notations can be a great way to keep confusion at bay.
Set up version control
While it’s good to keep your ERD updated, it is also necessary to ensure you have the old versions handy. Turn version control on or maintain copies of past versions.
Delightful Visual Project Management with ClickUp
A business is more than the sum of its parts. In reality, the competitive advantage of the business is the relationship between its parts, be it people, technology, systems, or data.
A good entity relationship diagram maps these connections and provides a clear bird’s eye view. You can use it to add connections, remove bottlenecks, trace root causes, or increase value.
ClickUp supports you with all this and more. Create unlimited ERDs with ClickUp Whiteboards. Convert elements into tasks for immediate action. Assign users, seek feedback, annotate, add comments, and elevate your ERDs. Try ClickUp for free today.