Is ERD considered a kind of UML diagram?
I have another idea. I think we should look in-depth.
When we are talking about ERD (Entity Relationship Diagram), we are talking about Entity Relationship Modeling.
It is firstly introduced by Peter Chen (1976). He has two famous articles on Entity Relationship Modeling (see first and second articles)
He talked about Entity-Relationship Modeling (not Entity-Relationship Diagram). It is ER Model.
There is another paper in 1975 about Modeling the Real World System.
ER Modeling is (see reference, the second paragraph):
In software engineering an ER model is commonly formed to represent things that a business needs to remember in order to perform business processes. Consequently, the ER model becomes an abstract data model that defines a data or information structure that can be implemented in a database, typically a relational database.
Diagramming Convention Techniques
When we are talking about ER Modeling, there many diagramming convention techniques.
- Chen Notation (some links need translation)
- IDEF1X Notation
- Bechman Notation
- Martin notation
- (min, max)-notation of Jean-Raymond Abrial in 1974
- UML class diagrams
And other notations (see reference)
All of above notations are using for ER Modeling or Data Modeling.
There is no earth-shattering difference between UML notation and other ER notations. They all model the most important elements of data models.
Finally: UML is a set of standard graphical tools to model the whole or parts of a project. We can use UML (Class Diagram) for ER Modeling and name them our ER Models or ERDs. So we can say: this is my ERD in UML Notation.
This was the first search on Google:
Key Difference: UML stands for Unified Modeling Language. ERD stands for Entity Relationship Diagram. UML is a popular and standardized modeling language that is primarily used for object oriented softwares. Entity-Relationship diagrams are used in structured analysis and conceptual modeling
UML, as an object oriented notation, have nothing to data modeling. Lots times I read about attributes as data columns. It is not true. We can put to an attribute simple data or any complicated other object.
For data modeling (database, relational database) we use ERD diagram, for storing data in object systems we can use ORM (object relational model), it is mixed UML/Data model, if we use pattern like a active table or active record.
ERD is it's own thing. It's not in UML specification. You can download specification PDF from the link.
UML is a common notation/language for object oriented modeling and it includes a multitude of diagram types. ERD is a diagram for data modeling (attributes and relationships). Some structural UML diagrams are fairly similar in what you can model, but the concept is different.
Types of UML diagrams:
