Creating a Physical Model

What’s In This Chapter?

The objective of a physical model is to provide a database administrator with sufficient information to create an efficient physical database. The physical model also provides a context for the definition and recording in the data dictionary of the data elements that form the database, and assists the application team in choosing a physical structure for the programs that will access the data. To ensure that all systems-side needs are met, physical models are often developed jointly by a team representing the data administration, database administration, and application development areas.

When deemed appropriate for the development effort, the model can also provide the basis for comparing the physical database design against the original business information requirements — to demonstrate that the physical database design adequately supports those requirements, to document physical design choices and their implications (e.g., what is satisfied, and what is not), and to identify database extensibility capabilities and constraints.

ERwin provides support for both roles of a physical model: generating the physical database and documenting physical design against the business requirements. For example, you can create a physical model from an ERD, key-based, or fully attributed model simply by changing the view of the model from “Logical Model” to “Physical Model.” Each option in the logical model has a corresponding option in the physical model. So each entity becomes a relational table, attributes become columns, and keys become indices.

Once the physical model is created, ERwin can generate all model objects in the correct syntax for the selected target server – directly to the catalog of the target server, or indirectly, as a schema DDL script file.

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