Entity-relationship (ER) diagrams (ERDs) provide a way to document the entities in a database along with the attributes that describe them. There are actually several styles of ER diagrams. Today there are three major methods:
- the Chen model (named after the originator of ER modeling, Dr. Peter P.S. Chen),
- Information Engineering (IE, or crows feet), and
- Unified Modeling Language (UML).
If you are not including object-oriented concepts in a data model, it really does not matter which you use, as long as everyone who is using the diagram understands the symbols.
However, UML is specifically intended for the object-oriented environment and is usually the choice when objects are included.