There are several different methodologies for creating and analyzing data models. These methodologies differ considerably in the degree of rigor and formality of their approaches, and in the terminology used.
CA 2E takes a data-driven approach to data modeling: it uses the entity-relation (E-R) modeling method. An E-R model lists the significant business objects of an organization and the relationships between these objects.
The objects are called entities. Each entity has its own properties, called attributes, that distinguish it from another entity. For example, a company, person, or product is an entity; a company ID, a person's name, or a product code is an attribute.
The company entity can be described and uniquely identified by its attribute; for example, company ID. Other examples of unique identification might be a person by the person's name, or a product by a product code.
In CA 2E, an entity means a file, and an attribute means a field on the file. The associations between files or between a field and its file are called relationships.
CA 2E uses the basic English verbs, Known by, Has, Refers to, and Owned by, to represent these types of relationships. Relationships drive the design process. CA 2E is able to create the database for an application system entirely and automatically from the types of relationships it recognizes in a data model.
In addition, CA 2E uses what it knows about relationships and integrity rules stored in a data model to automatically generate default programs to implement an application.
For more information about entities, attributes, and relationships, see the chapter "Developing a Conceptual Model."
For more information about types of CA 2E relations and their use, see Chapter 3, "Understanding Your Data Model."
The following example illustrates a CA 2E data model for a simple Order Entry application. The model identifies the entities, and their relationships, and the types of the relationships using four basic relations.
To describe data models, CA 2E uses a simple data modeling language consisting of statements of the form:
<Subject Verb Object>
Example: A Customer has a Customer name
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