You can use a variety of techniques to create a SAM in PowerDesigner, depending on whether or not you have existing data models that can ‘seed’ the new model.

To create SAM (CDM) entities based on CDM entities in PowerDesigner models, copy them from the existing model, and paste them into the new model. It may be appropriate to paste them as replicas. To create SAM entities based on existing LDM entities, open the LDM, and choose Generate Conceptual Data Model from the Tools menu. Ensure that you update the new SAM (it will need to be open), rather than creating a new model, and that you do not keep the generation dependencies. An entity in the SAM is very likely to be related to many LDM entities, so we suggest you maintain the links from the SAM to LDMs another way, which we will describe shortly.

To create attributes based on data items in a ‘Data Dictionary’ model held in a different CDM, copy the data items from the Data Dictionary model, and paste them as shortcuts or replicas in your SAM.

Use the Excel Import facility to create or update entities in your SAM. This is a great way of making effective use of existing documentation.

In order to achieve the potential benefits of a SAM, it must communicate concepts clearly. Of all data models, this is probably the one where style and format matter the most. Look back at the figures in this chapter, and you will see that we have taken more than one approach regarding the content of symbols – revise the symbol content to suit the audience. As this is a monochrome book, we have not been able to use color in our symbols apart from some shading, but you can use color very effectively in a SAM, and even continue the color scheme to other related models.

Be prepared to create more than one diagram in your SAM, if you need to communicate your message to different audiences. For layout and formatting tips, refer to Chapter 9 in Data Modeling for the Business: A Handbook for Aligning the Business with IT using High-Level Data Models, ISBN 9780977140077, where the SAM is referred to as a High-Level Data Model, or HDM.

Every organization’s modeling requirements are different, so every organization’s model linking requirements are different. See Chapter 18 for a discussion of this topic.

Linking a SAM to other related models is great for impact analysis, and for categorizing the content of related models. The relatively abstract nature of the entities in a SAM means that they are unlikely to match directly to entities or tables in other data models, except those in other SAMs. We suggest that you do not use generation links to link the SAM to other models, even if you generated parts of the SAM from other models. You could use the mapping editor to create these links, but we believe that these links need to be more explicit and obvious than those created by the mapping editor. Instead, we suggest that you use traceability links.

Create a new type of Traceability Link, named according to the reason why you are linking models together. Create Traceability Links between the objects you need to connect together, perhaps using a Dependency Matrix. See Exercise 19 for an example of this approach. You could share standard Dependency Matrices via template models or a model extension.

When the linked models are in the repository, the links will show up in repository searches and impact analysis (assuming you select Use Repository). You may want to create your own analysis rules to make this easier for users.

You can also create links between the subject areas in a SAM and diagrams in other models by using the Related Diagrams feature.

The diagrams in the SAM are simple, and there is no need for complex naming standards for relationships. We suggest you take one of three approaches, listed in Table 15.3.

Table 15.3 Relationship names in the SAM

Approach

When to use

Let the relationship names default, or provide simple unique names; don’t display them on diagrams; do not create relationship role names

Use in a high-level BSAM, where most or all relationships are many-to-many, and are therefore difficult to name precisely.

Create relationship names that include entity names; do not create relationship role names

Use when you do not want to show relationship names on diagrams, but you need to have a meaningful list of relationships in the Browser, the portal, or in reports

Create relationship names that include entity names; also create relationship source role names

Use when you need to have a meaningful list of relationships in the Browser, the portal, or in reports, and you also want to show a shorter name on diagrams. Also use when you want to generate Assertion Statements.

PowerDesigner allows you to verify the validity of your models via the Model Check facility (press <F4> to run the model check). The following checks are particularly useful for a SAM. Check the PowerDesigner documentation to find out more about them.

·         Name or Code contains terms not in glossary [if glossary enabled]

·         Name or Code contains synonyms of glossary terms [if glossary enabled]. PowerDesigner can automatically correct these for you by replacing synonyms with their associated glossary terms.

·         Existence of attributes

·         Existence of relationship or association link(s)

·         Redundant inheritance

·         Multiple inheritance

·         Parent of several inheritances

·         Reflexive dependency

·         Reflexive mandatory

·         Bijective (completely mandatory one-to-one) relationship between two entities

·         Existence of inheritance link

“Checking a Data Model” (Data Modeling)

If you have documentation of requirements or business rules, consider importing them into PowerDesigner, and linking them to your SAM entities and relationships.

Make the SAM available to as wide an audience as you can. If you do not have a repository, generate an HTML report and add it to your intranet; generate an RTF report, including diagram images, and distribute in whatever format suits you best; use the Excel export and import features to enable non-users to contribute.

If you have a repository, ensure that the SAM and all linked models are checked in, and made available to the portal, and use the ‘Composer’ license to allow selected experts to amend the SAM via the portal.

In PowerDesigner, create the BSAM shown in Figure 15.3.

Identify an area within your organization that is in desperate need of a SAM and build it for them using the ten-step approach from this chapter. Make sure you document it in PowerDesigner as a CDM.

If you prefer, build one or more of the Subject Area Models described in this chapter.

 

Key Points

·         A subject area is a concept that is both basic and critical to your audience.

·         A subject area model is a set of symbols and text that represents key concepts and the rules binding these key concepts for a specific business or application scope and for a particular audience.

·         The BSAM is a subject area model of a defined portion of the business.

·         The ASAM is a subject area model of a defined portion of a particular application, and may be relational or dimensional.

·         The CSAM is a subject area model that shows how something new fits within an existing framework.

·         Follow the ten-step approach to building a SAM.

·         The CDM is the most appropriate type of model for a SAM in PowerDesigner.

·         Pay attention to how you present the SAM to your audience(s).

·         Use the PowerDesigner repository and portal to share and link your SAM.

·         There is no need for complex relationship naming standards.

 

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