In this article we’ll discuss how the new Diagramming features in ERwin R8 can help the modeler re-design Subject Area allocation and Diagram utilization.
In versions of ERwin prior to R8, the modeler would create Subject Areas to represent subsets of the data for design, engineering or implementation purposes (for instance a phased release). Subject Areas would also be beneficial for abstraction or to focus changes to a specific set of objects, introducing a limited-scope synchronization, or to assist with sub-modeling efforts within Design Layers.
Similarly, Stored Displays would be used to depict the various display levels, with Attribute/Column or Table/Entity being the most common choices. Extensions to the Dimensional notation allowed the Stored Display to collapse the Fact or Dimension tables so that particular attention could be paid to areas of the Diagram where needed. The Stored Displays ultimately would then be used to drive reporting either via the File…Print function or out of the Report Template Builder (RTB).
In R8 we see radical changes to the way in which the objects are displayed within the model, that offers a number of opportunities within the Dimensional modeling space.
Of note here is a summary of the R8 changes that are important in this area of focus:
- Diagrams replace Stored displays, and a Table within a Subject Area may or may not appear in the Diagram that is owned by the Subject Area
- A Subject Area can have associated with it many Diagrams (or none at all – there is an application for this which I’ll get to in future editions)
- The model need not have a Main Subject Area (MSA) and it’s associated Diagram, which simplifies diagram creation and management, and allows you to intentionally duplicate objects for the purpose of abstraction or specificity, which is quite taboo within OLTP applications, but defendable within the DW/Dimensional model space
- Themes are introduced in R8, which exist at many levels, from Model to Diagram, all the way down to Table. Columns can also have their own custom display levels and properties, which is a big benefit to the Dimensional model
- The new Display Level of “Keys” allows only Key fields to be displayed
There are many other new features, but let’s focus on these ones for now. The fact that a Subject Area can “own” many Diagrams presents great opportunities to the Dimensional modeler, since the Subject Area can now be more closely aligned with the Data Mart, and the Diagrams can represent “integrations” of the Data Mart to provide distinct interpretations of the Data Mart.
In the Subject Area below we have different Diagrams from the same Subject Area, each illustrating a specific analysis scenario around the same Fact.
“Problem” Subject Area with 3 Diagrams containing Tables with their own display features:
The ability to depict Diagrams within the Subject Area with different objects and abstractions levels offers the following benefits:
- Allows the model viewer to easily see what the analysis scenarios are. This will enable users to better understand the tables and relations to navigate, and also more precisely explain the limited data required to answer a specific need
- It also allows the data mart designer to focus on the more important tables/relations within the Subject Area to deliver the optimum design. A data mart designer could choose to build materialized views /cubes based upon the maximum required data, but not to include all of the data within the deployment
- Allow the ETL programmer to understand and map the needed data for a specific change request. The team can better appreciate the difference between relatively simple transformations, and those that require complex joins or a large number of tables/columns
- This also allows the DBA to pay particular attention to “hot spots” and identify potential performance problems during the design phase (design before release…an old tradition that is making a come back)
So now that you have the ability to depict a number of different Diagrams within a Subject Area, think about the real purpose of those Subject Areas before converting your models to R8. You may be surprised by the fewer numbers of SA’s that you have…