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:

1. the Chen model (named after the originator of ER modeling, Dr. Peter P.S. Chen),
2. Information Engineering (IE, or crows feet), and
3. 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.