You want to know what entity relationship model is? This ER diagram guide covers their usage, history, symbols, notations, and how to use our ER Chart Tool. We have also added some ER diagram templates so you can also see how to jump right in with the templates.
What is an ER-Diagram?
A Entity Relationship Diagram (ERD) is a visual representation of different entities within a system and their relationship to each other. For example, the elements writer, book, and a consumer can be described using ER diagrams as follows:
You are also ERD or ER models known. Click on the links below if you would like to learn something specific about ER charts.
History of ER diagrams
Although data modeling became a necessity around the 1970s, there was no standard method for modeling databases or business processes. Although many solutions were proposed and discussed, none of them found wide acceptance.
Peter Chen is credited with introducing the widely used ER model in his paper "The Entity Relationship Model-Toward a Unified View of Data". The focus was on entities and relationships, and he also cited a diagram representation for database design.
His model was innovated by the data structure diagram introduced by Charles Bachman. One of the earlier forms of ER diagrams, the Bachman diagrams, are named after him.
A detailed history of ER diagrams and data modeling assessment can be found in this article.
Use of ER diagrams
Which use of ER diagrams there is? Where are they used? Although they can be used to model almost any system, they are used primarily in the following areas.
Entity relationship model in database design
They are often used for the design of relational databases. The entities in the ER schema become tables, attributes and convert the database schema. Because they can be used to visualize database tables and their relationships, they are also commonly used to troubleshoot databases.
ER Diagrams in Software Engineering
Entity-relationship diagrams are used in software engineering during the planning stages of the software project. They help identify various system elements and their relationships to each other. It is often used as the basis for data flow diagrams or DFD’s as they are commonly known.
For example, inventory software used in a retail store will have a database that monitors items such as purchases, items, item type, item source, and item price. The representation of this information by an ER diagram would be something like this:
In the diagram, the information inside the oval shapes are attributes of a particular entity.
ER Diagram Symbols and Notations
There are three Basic elements in an ER diagram: Entity, attribute, relationship. There are other elements that are based on the main elements. They are weak entity, multi-valued attribute, derived attribute, weak relationship and recursive relationship. Cardinality and ordinality are two other notations used in ER diagrams to further define relationships.
An entity can be a person, place, event or object relevant to a particular system. For example, a school system may include students, teachers, major courses, subjects, fees, and other elements. Entities are represented in ER diagrams by a rectangle and named with singular nouns.
A weak entity is an entity that depends on the existence of another entity. In more technical terms, it can be defined as an entity that cannot be identified by its own attributes. It uses a foreign key that, together with the primary key assigned to it, forms the primary key. An entity like order item is a good example of this. Without an order, the order item is meaningless, so it depends on the existence of the order.
An attribute is a property, feature, or characteristic of an entity, relationship, or other attribute. For example, the attribute is an attribute of the entity an inventory item. An entity can have as many attributes as needed. Meanwhile, attributes may also have their own specific properties. For example, the attribute "customer address" may have the attributes number, street, city, and state. These are called composite attributes. Note that some top-level ER diagrams don’t show attributes for simplicity’s sake. However, in those that do, the attributes are represented by oval shapes.
When an attribute can have more than one value, it is called a multi-valued attribute. It is important to note that this is different from an attribute having its own attributes. For example, a teacher entity can have multiple subject values.
An attribute based on another attribute – this is rarely found in ER diagrams. For example, this can be represented with a circle.
A relationship describes how entities interact. For example, the entity "carpenter" may be related to the entity "table" by the relationship "builds" or "makes". Relationships are represented by diamonds and labeled with verbs.
When the same entity participates in a relationship more than once, it is called a recursive relationship. In the following example, an employee can be a supervisor and be supervised, so there is a recursive relationship.
Cardinality and ordinality
These two further define relationships between entities by putting the relationship in the context of numbers. For example, in an email system, an account may have multiple contacts. The relationship in this case follows a "one to many" model. There are a number of notations that can be used to create the Representation of cardinality in ER diagrams are used. Chen, UML, crowfoot, Bachman are some of the popular notations. Creately supports Chen, UML, and Crow footnotes. The following example uses UML to represent cardinality.
How to draw ER diagrams
The following points show how to create an ER diagram.
- Identify all entities in the system. An entity should only appear once in a given diagram. Create rectangles for all entities and name them correctly.
- Identify relationships between entities. Connect them with a line and add a diamond in the middle to describe the relationship.
- Adding attributes for entities: Provide meaningful attribute names so they are easy to understand.
Just sounds right? In a complex system, identifying relationships can be a nightmare. This is something that can only be perfected with practice.
Best practices for entity relationship models
- Provide a precise and appropriate name for each entity, attribute, and relationship in the diagram. Terms that are simple and familiar. When naming entities, remember to use singular nouns. However, adjectives can be used to distinguish entities that belong to the same class (z.B. Part-time and full-time employees). Meanwhile, attribute names must be meaningful, unique, system-independent, and easy to understand.
- Remove vague, redundant, or unnecessary relationships between entities.
- Never connect one relationship to another relationship.
- Use colors effectively. You can use colors to classify similar entities or to highlight key areas in your diagrams.
Drawing ER Diagrams with Creative Means
You can Draw entity relationship diagrams manually, especially if you are just informally showing simple systems to your colleagues. However, for more complex systems and for external audiences, you need an ER model tool like this from Creately to create visually appealing and accurate ER diagrams. Offered by Creately as an online service, it is quite easy to use and much more affordable than buying licensed software. It is also great for development teams because of its strong support for collaboration.
ER diagram templates
Below are some ER Diagram Templates, so you can get started quickly. Click on the image and on the new page that opens, click the "Use as Template" button. For more templates, see the ER Diagram Template section.
A basic ER diagram template to get you started quickly:
Advantages of ER Diagrams
ER diagrams provide a very useful framework for the Depict creation and modification of database relationships. First, ER diagrams are easy to understand and do not require extensive training to work with them efficiently and accurately. This means that anyone can use ER diagrams to easily communicate with developers, customers, and end users, regardless of their IT expertise. Second, ER diagrams translate easily into relational tables that can be used to quickly build databases. In addition, ER diagrams can be used directly by database developers as a kind of conversion plan for implementing data in specific software applications. Finally, ER charts can also be used in other contexts, e.g.B. to describe the various relationships and processes within an organization.
Tutorial: Feedback on the Entity Relationship Model
I did my best to cover everything you need to know about the Entity Relationship Model. If you think I missed something, please mention it in the comments. It’s also a good place to ask questions. If a question is frequently asked, I will include it in the frequently asked questions section.