Rules all around us

Relationships tell the tale

Connecting the dots


The relationships between data entities are as important as the definitions of entities and elements that we’ve discussed in the previous chapters, and are key to understanding business requirements. This chapter defines rules and relationships and the three different levels at which relationships can exist: conceptual, logical, and physical. Data rules are distinguished from action rules. Cardinality and labels are explained so that you can read any data model as easily as reading a book. Other types of relationships, such as recursive relationships and subtyping, are discussed as well. Hands-on examples of how to create the various relationship types in CA ERwin ...

Get Data Modeling Made Simple with CA ERwin Data Modeler r8 now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.