The star schema
- Build the fact query subject with the measures you want in your reports.
- Build related query subjects to give context to the measures.
- Generate the model.
At any time, you can hover pause the pointer mouse over an object to view its properties. The properties show the origin of the object in the data source. In the Explorer Diagram view, you are also shown if the item is used in the star schema. You can right click on a join to view the Relationship Dialog.
You should save your design as you work. If you exit Model Design Accelerator and then return, you can resume working on the saved star schema.
Build the fact query subject
Use the Explorer Tree to explore the tables and columns in your data source. Select the measures that you want to include in your reports and add them to the fact query subject in the Model Accelerator workspace. Measures are numeric columns in a database table or view that can be grouped or aggregated. Examples of measures are Production Cost or Quantity. Model Design Accelerator tracks the required keys and automatically includes them in the model. There is no requirement to add keys. Select only the measures you want report authors to see in your package.
Select measures in the Explorer Tree and drag them onto the fact query subject in the Model Accelerator workspace. You can also make your selections from the Explorer Diagram.
All the measures being added must be from the same table in your data source. If you try to add measures from multiple tables, or add query items that are not measures, the Model Warning dialog box will display. This is because Model Design Accelerator supports only a single fact table star schema model.
Build related query subjects
Use objects from the Explorer Tree to build the query subjects in the star schema model. Select columns from the Explorer Tree and add them to the appropriate query subjects in the Model Accelerator workspace. You can add or remove query subjects or columns from the workspace as required.
To help you build the query subjects, use the Explorer Diagram to examine the metadata for the tables and views that you selected from the data source. You can create query subjects from either the Explorer View or the Explorer Diagram.
From the Explorer Diagram, you can select one query subject or many and view the relationships.
Generate your model
When your star schema is complete or ready for testing, click Generate Model to build the model and enter IBM® Cognos® Framework Manager.
The Model Advisor tests are applied to the resulting model. In the Verify Model Results tab, review the issues that are identified. There is a description of each issue and a list of objects that are impacted by the issue. For more information on the Model Advisor, see Analyzing models.
The star schema model that you created will usually contain only a subset of query items from the data source. When you generate a model, only the metadata that is required to support your star schema model is imported into Framework Manager.
Each time you generate a model, new namespaces are created in the open Framework Manager project. The Physical View contains only the tables that were imported to support the star schema model. The Business View contains model query subjects with only the columns you selected when building the query subjects. These are the objects you built in Model Design Accelerator. The Presentation View contains a collection of shortcuts referencing the model query subjects in the Business View.
From Framework Manager, you can enhance the model by adding calculations, filters, additional languages, and dimensional structures. However, each time you generate a new model, new namespaces are created and your enhancements are not applied to the new namespaces.
You can return to Model Design Accelerator at any time to edit your star schema. You must publish the model in Framework Manager to use it in the IBM Cognos studios.