Work with Subject Areas

This topic provides information about how to create and modify the presentation layer's subject areas.

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About Creating Subject Areas

There are several ways to create subject areas in the presentation layer.

Oracle recommends that you drag and drop a business model from the logical layer to the presentation layer, and then modify the presentation layer based on what you want users to see. You can move columns between presentation tables, remove columns that don't need to be seen by the users, or even present all of the data in a single presentation table. You can create presentation tables to organize and categorize measures in a way that makes sense to your users.

You can also duplicate an existing subject area and its corresponding business model. Or you can create an empty subject area.

Although each subject area must be populated with contents from a single business model, you can create multiple subject areas for one business model. Creating multiple subject areas for one business model makes it easier for the users to work with the content and create queries that span multiple subject areas.

There are many ways to create multiple subject areas from a single business model. One method is to drag a business model to the presentation layer multiple times, then edit the properties or objects of the resulting subject areas.

For example, suppose you have a business model called ABC that contains the Geography and Products dimensions. When you drag it to the presentation layer twice two subject areas are created with the default names ABC and ABC#1. You then edit the subject areas as follows:

Rename the ABC subject area to DEF, then delete the Geography presentation hierarchy
Rename the ABC#1 subject area to XYZ, then delete the Products presentation hierarchy

Users can then run queries that span the DEF subject area containing the Products hierarchy, and the XYZ subject area containing the Geography hierarchy.

When you query a single subject area, all the columns exposed in that subject area are compatible with all the dimensions exposed in the same subject area. However, when you combine columns and dimensions from multiple subject areas, you must ensure that you don't include combinations of columns and dimensions that are incompatible with one another.

For example, a column in one subject area might not be dimensioned by Project. If columns from the Project dimension from another subject area are added to the request along with columns that aren't dimensioned by Project, then the query might fail to return results, or cause the error, "No fact table exists at the requested level of detail: XXXX."

About the Implicit Fact Column

For each subject area in the presentation layer, you can set an implicit fact column.

The subject area's specified implicit fact column is added to a query when it contains columns from two or more dimension tables and no measures. The column isn't visible in the results. It's used to specify a default join path between dimension tables when there are several possible alternatives or contexts.

If an implicit fact isn't configured, then the Oracle Analytics query engine uses any fact table source to answer dimension-only subrequest that contains multiple dimensional references but no fact reference.

The Oracle Analytics query engine can also use any fact table source if the configured implicit fact column isn't relevant to the dimensions that are joined. This could happen, for example, when implicit fact column is a level based measure at a level higher than the dimensional only subrequest.

You use the Implicit Fact Column field in the subject area's General tab to add, remove, or replace the implicit fact column. See Create a Subject Area.

Create a Subject Area

Manually create a subject area when you can't drag and drop a business model from the logical layer to the presentation layer.

You use logical content from a single business model to build the subject area. Subject areas can't span business models.

You can select the Hide if field and write an expression to hide a subject area. See Write an Expression to Hide a Presentation Object.

Semantic Modeler doesn't create an alias when you change a subject area's name. If you need to track a subject area's previous names, then Oracle recommends that you use the Alternative Names field to create and manage alternative names for the subject. For more information about alternative names, see About Alternative Names for Presentation Objects.

On the Home page, click Navigator and then click Semantic Models.
In the Semantic Models page, click a semantic model to open it.
Click Presentation Layer.
Click Create and then click Create Subject Area.
In Create Subject Area, go to the Name field and enter a subject area name.
Go to Business Model and select the business model to associate with the subject area.
Click OK.
In the subject area, click General to set the subject area's general properties.
Optional: In the Description field, enter a description that is displayed when a user creating visualizations or analyses hovers over the subject area in the data sources list.
Optional: In the Implicit Fact Column field and click Select to browse for and select the fact column you want to use.
In the Alternative Names field, enter an alternative name for the subject area.
Optional: Select the Hide if field and provide an expression that controls whether the subject area is available to users when they create visualizations and analyses.
Click Save.