ER/Studio - Embarcadero Technologies Product Documentation

USING ER/STUDIO > DEVELOPING THE LOGICAL MODEL
Notes
• You can map an entity to tables in disparate physical models.
• Once you have created a user-defined mapping, to view the mapping you can open a Table Editor or Entity Editor
and then select the User-Defined Mappings tab.
• You can also edit the mappings from the User-Defined Mappings tab in the Table Editor or Entity Editor by
right-clicking the model you want to editor and clicking the Edit option. When editing the user-defined mappings,
you can also edit the definition and the attachments bound to the user-defined mapping.
Enforcing Data Integrity Using Check Constraints
The Check constraint evaluates the data as it is entered and only if the check evaluates to true is the entry allowed.
The constraint entered for an entity is used when creating the physical model and can be seen in the table’s DDL.
1 Double-click the entity or table you want to create a check constraint for.
2 On the Rule/Constraints tab of the Entity or Table Editor, name the constraint and then enter the constraint in
the text box.
The constraint is added to the CREATE TABLE statement in the Table’s DDL in the format:
CONSTRAINT (constraint_name) CHECK (constraint_text)
where
constraint_name is the name of the constraint
constraint_text is the text entered in the text box
NOTE: Constraints are created in the Data Dictionary, in the Rules folder. For more information, see
Promoting Data Integrity Through Rules.
Developing the Logical Model
A logical model is developed before the physical model. It addresses the business and functional requirements of
systems development. The logical design allows you to determine the organization of the data that you need to store
in a database before you create the database; it serves as a blueprint.
To design the most effective data model possible, you should focus on the logical design before developing the
physical design. Both the logical and physical design processes are complex so it is best to separate rather than to
mix the two. A sound logical design should streamline the physical design process by clearly defining data structures
and the relationships between them.
A data model can be extremely useful for other things besides creating databases, though that is generally its primary
purpose. In systems development, the goal is to create an effective database application that can support some or all
of your enterprise. However, a data model of your business can help you define operational aspects of your business
that you might otherwise overlook. Also, a well-defined data model that accurately represents your business can be
helpful in orienting employees to goals and operations. The data model can also serve as an invaluable
communications tool for both internal and external constituents.
For more information, see the following topics:
• Logical Design Concepts
• Creating and Editing Entities
• Creating and Editing Attributes and Columns
EMBARCADERO TECHNOLOGIES > ER/STUDIO® 8.0.3 USER GUIDE 111