Modeling Entity Relationships › Introducing the Diagrammer

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Introducing the Diagrammer

Typically, the first step in creating a business application is creating a data model. In the data model, you specify how real-world entities are represented in a database. Diagrams enable you to visually communicate the specifics of an application’s data model to other developers or business analysts, and in some cases, to your end users.

With the project management application you are designing, the real-world entities map quite easily into database objects. The application tracks projects, the tasks that make up those projects, and the employees that are assigned to those tasks. Projects, tasks, and entities are each represented by one entity.

When you have identified the data structures you need, you can represent this information visually using design diagrams. The CA Plex Diagrammer enables you to create these diagrams, and define objects and their relationships. When you create entities and relationships using the Diagrammer, the corresponding triples are automatically added to your model.

 

 

Introducing the Diagrammer

 

In this chapter, you use the Diagrammer to create a diagram of the data model behind the sample application (left). In the process, CA Plex creates the Task entity for you, along with triples representing relationships between the entities.

In CA Plex diagrams, objects are represented by boxes (or other shapes) called nodes. A relationship between two objects is represented in one of two ways:

In the diagram that you create, the nodes represent entities.

Together, two nodes and the link between them, or a node and its sub-node, represent a triple in an CA Plex model. For example, the diagram of the project application has an owned by link that relates the Task entity to the Project entity. This corresponds to the following triple:

Task owned by Project

When you define and change objects using the Diagrammer, your changes are reflected everywhere in the model. Similarly, if you delete a triple in the Model Editor, any corresponding links on diagrams are also removed.