An entity relationship (ER) diagram shows how people, objects, or concepts relate to each other within a process or system.
Entity diagrams are commonly used in software engineering, business information, education, and research for mapping and modeling.
For example, a developer may use an ER diagram to show data pathways in a relational database and how it flows through a system.
They are similar to a data structure diagram (DSD). While DSDs depict the relationship of elements within entities, ER diagrams show the relationship between entities.
Therefore, ER diagrams serve a very different purpose to organization charts.
ER models use a set of entity shapes (symbols) that describe the relationship between entities. This includes errors and connectors, along with the use of nouns to describe entities and verbs to show relationships.
Here are the most common:
Source: SmartDraw (link shown below)
Entities are represented by rectangles — an object or concept that you want to store information. There are two different entity types as well.
Strong entities are not dependent on any other entity within your schema. It will be represented by a single rectangle and always has a primary key.
Weak entities are dependent on a strong entity. In other words, without a relationship to a strong entity, it would not exist. Also known as an identifying relationship, a weak entity is depicted as a double rectangle.
An action is represented by a diamond shape, which shows how entities share information within a database. Relationships between strong entities and weak entities in entity sets are depicted by using a double diamond shape.
In some cases, entities may be self-linked, such as the case when a manager supervises employees.
An attribute is the unique characteristics of an entity and is depicted by an oval. An employee’s ID number or social security number might be the data inside an attribute,
There are also different types of attributes.
A multivalued attribute contains more than one value and is shown as a double oval. An example would be when you are listing the multiple skills an employee has.
A derived attribute is one that is based on another attribute. It is depicted by a dotted-line oval. An example would be an employee's pay, which is determined by the number of hours worked.
Relationships between entities are shown using solid lines. Depicted on lines is what’s called 'cardinality'. Cardinality helps users understand how many instances of an entity relate to another.
There are several ways this is expressed, although the most common is the information engineering style, which shows relationships as:
"Cardinality"
Other ways of defining relationships are the Bachman style, Chen style, Barker style, or Martin style, which use different symbols or numbers to define relationships.
Entity relationship diagrams are used in a variety of different ways in different industries. Here are a few examples of how ER diagrams might be used:
Research often starts with a large volume of raw data that needs to be cleansed to be useful. Using an ERD, researchers can better organize their structured data to create a database of usable data.
An efficient business information system requires streamlined and efficient processes. It helps managers to understand the complex interdependencies between entities.
Entity relationship diagrams are created to design a relational database and help to define the requirements and structure for information systems. ERDs can demonstrate these different types of models.
ERDs are commonly used in conjunction with a data flow diagram and can also be helpful when troubleshooting problems in a database. For example, when there is a disconnect between logic and result, an ER diagram can help in showing the relationships to narrow down what relationships are missing or incomplete.
ER diagrams are used in software engineering during the early stages of planning projects. They help to identify the different elements and define relationships.
Entity relationship diagrams are used in education to visually represent the relationships between students, teachers, and schools. ERDs can also be used to maintain relationships between entities related to educational drivers.
ER Diagram (Education)
Original Source Concept: EDraw Max
An efficient ER diagram can help you understand the relationships between each and every entity within your system, process, or organization. Here is a simplified step-by-step guide on how to create an entity relationship diagram manually.
Before you begin, you want to think about the purpose of drawing an ERD. This will help you decide whether you want to build a conceptual, logical, or physical model and the right level of detail you need to add.
The first step is to identify the entities that will be used within your diagram. Each entity should be depicted as a rectangle and a description of the information that will be stored within each rectangle. You will want to show them on a page, but spread them out so there is room between them to show relationships.
Next, you need to look at each entity and decide if they have a relationship. If they do, you draw a solid line connecting them.
In this step, you are depicting how the entities are related. Draw an action diamond between the two entities and include a short description of how the relationship works.
Next, use oval-shaped symbols to add any key attributes associated with entities.
Finally, you will want to continue to examine each entity and look for associations. Continue to add relationships and describe them. Be aware that some entities will be stand-alone without any relationships, while others may have multiple relationships.
After you’ve completed your ERD, you will need to review it for accuracy.
Some common mistakes include:
An important step in this review is to examine each relationship to see if there is a more efficient solution to define the relationship or to reduce redundancies.
You may also want to consider adding colors to highlight the important parts of your ERD to make them stand out.
ER diagrams are ideal for many scenarios, but there are limitations. For example, ERDs are not the best way to diagram the structure of an organizational chart.
Here are some of the top benefits and limitations of entity relationship diagrams.
ERDs are not effective for org charts. A better way would be to use Functionly.
You can create complex, beautiful org charts in minutes. With our 'drag and drop' org mapping, it’s easy.
One of the major advantages of using Functionly is that you can build multiple scenarios. This allows you to envision changes to your org structure, such as during periods of rapid growth, and help identify gaps and future needs.
Functionly also integrates with many of the tools businesses are using, such as ADP, Zenefits, QuickBooks, Gusto, Slack, Justworks, Bamboo HR, Rippling, and more. (If you don’t see an integration you need, please request this using our Contact page.)
These integrations allow you to seamlessly build org charts and connect data. For example, you can monitor live headcounts, open positions, and other stats about your teams.
Want to see Functionly in action? Start with a free org chart demo to see how easy it is to be robust and flexible org charts for your organization.
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Resources for ER Diagrams:
Image Credits
Title header image: Image created by Functionly.