Making Data Models Readable - High-Performance Web Databases: Design, Development, and Deployment - page 244

Exhibit 16-5. Shlaer and Mellor cardinality and optionality.
each is mandatory (*) or optional (.). These additional symbols add infor-
mation without cluttering the overall model.
Some techniques (object-role modeling and Chen) go a step further, how-
ever, by showing attributes in additional circles (or ellipses) on the drawing.
Chen's notation is shown in Exhibit 7. This greatly increases the number of
symbols that must be on a page, thus making the model more complex.
Object-role modeling takes the unusual approach of not distinguishing
graphically between attributes and entities. This is based on the premise
that the relationship between an attribute and an entity is conceptually
the same as a relationship between two entities. While this also makes
the model more crowded than the notation shown previously, the consol-
idation of entities and attributes actually reduces the number of kinds of
symbols by one. The “not too many objects” rule still applies, though, and
this will require the domain of each drawing to be smaller. Exhibit 7
shows an example using object-role modeling, where the relationships
Exhibit 16-6. Attributes.