A subject area is a subset of objects taken from the whole pool of objects in your model. You can create multiple subject areas in your model. Typically, you create a subject area to help you manage a large model, to reduce the number of objects that you work with, or to focus on a particular business function.
Working with subject areas is especially useful when designing and maintaining a large or complex data model. By dividing the Main Subject Area into several smaller subject areas, you can allow different groups within an organization to concentrate on the processes and tasks pertinent to their own business area.
You create a subject area in the Subject Areas editor, which includes options for selecting the members of a subject area. In the Subject Areas editor, you name the subject area, set global options, and select members to include in the logical model or the physical model, or both. You can also exclude references, during schema generation, to tables in the Main Subject Area that are not in the currently selected subject area. In addition, you can use the Spanning Neighborhood feature to specify how many generations of ancestors or descendants, or both, of the members you select to include in a subject area.
By default, a new data model includes one subject area (Main Subject Area) and one stored display (Display 1). For each subject area you create, its name is added to the Subject Area list in the Model Explorer. You can switch to a different subject area by selecting the area from the list. If you have multiple subject areas in your model, you can create a unique set of stored displays for each subject area. When you switch to a different subject area, you only see the stored display tabs for the current subject area.
When you create a subject area for a logical model, a similar subject area is automatically created for the physical model. The same applies if you create a subject area for a physical model; a similar one is automatically created for the logical model. If you add or remove members from a subject area, the membership change is reflected in the corresponding physical or logical model but will not affect the membership of any other subject area. If you add or delete objects in one subject area, such as entities and attributes, it does not impact the other subject areas.
Some display options apply to all the subject areas in the model. For example, if you change the background color or the color of a particular object, the new color applies to every subject area and stored displays. Similarly, if you set the width or height of entities, tables, or views to a specific value, the height and width change in every subject area and stored display.
When you create or edit a subject area, the new subject area or the edits are saved when you close the Subject Areas editor. When you save a model to an .erwin file, the subject areas are saved with the model, not as individual files. When you open a model, all previously created subject areas are available. In a logical/physical model, the logical and physical models share the same subject areas.
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