3.      The Glossary

o        PowerDesigner automatically builds links from glossary terms to the objects that reference those terms in their names

4.      Models that the LDM was generated from

o        PowerDesigner automatically creates and updates Generation Dependencies, unless you tell it not to when generating or updating a model

5.      Models that have been generated from the LDM

o        PowerDesigner automatically creates and updates Generation Dependencies, unless you tell it not to when generating or updating a model

Generation Dependencies are broken if you move attributes between entities

6.      Models representing equivalent data structures that are not connected via a common Subject Area Model

o        Use a specific type of traceability link – see Exercise 19 for instructions

7.      Dimensional LDMs containing data derived or calculated from data in a Relational LDM

o        In the Dimensional LDM, create Traceability Links from derived or calculated attributes to the attributes in the Relational LDM – this is described in Exercise 19

Remember, links between models can be seen in the list of Target Models on the Model menu.

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 tailor the analysis results to suit your users.

Dependency Matrices provide a useful way of visualizing and managing links.

You can also create links between objects in a LDM and diagrams in other models, using the Related Diagrams feature.

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.

There is no specific notation for Dimensional models in the LDM, but there is an easy way to annotate your diagrams to identify the dimensional model concepts we discussed earlier in this chapter. We can use the standard Stereotype property, as shown in Figure 16.26.

Figure 16.26 Stereotypes in a dimensional LDM

If you want to use different symbols, depending on the entity stereotype, you can, though it is not a two-minute job, unlike the minor customization needed to add the two lists of stereotypes mentioned in Figure 16.26. See Exercise 19 to find out how to add the stereotypes. Adding icons to indicate the Dimensional Type is fairly simple, as long as you have suitable icons. You can see an example of this later, in Figure 17.12.

In a LDM, you need to be stricter with relationship names than in a SAM. We suggest you create meaningful names for your relationships, and create role names. If you have included %PARENTROLE% in the foreign attribute name template in your migration settings, make sure your role names have initial capital letters, so they meet the naming standards for attributes. See “Relationship Properties”, in Chapter 13.

There is no automated process for normalizing a data model in PowerDesigner. The tool cannot possibly understand your business or your model well enough to tell you how to alter the model. The following techniques will help you to amend your model.

·         Convert any relationship into an entity

o        Right-click the relationship symbol, and select Change to Entity

o        Use this technique when your analysis reveals that there is data involved in a relationship, and a new entity is required

·         Replicate Attributes

o        Useful if you need to have identical attributes in sibling subtype entities

·         Let PowerDesigner rename Foreign Key Attributes for you, using the relationship role name as a prefix

·         Copying and moving attributes

o        Use drag and drop between symbols, in the Browser, or between symbols and the Browser

·         Copy and paste an entity to create an almost identical copy

o        See Chapter 10 to remind yourself of the limitations of copying this way

·         To copy part of a diagram, complete with display preferences, select at least two symbols, and select Create Diagram from Selection from the contextual menu

·         Use the Hierarchical layout to make entity hierarchies really obvious

·         Save versions of your model in the repository

·         Before you introduce abstraction in your LDM, make sure you take a copy or version of the LDM so you have something to go back to; or maintain the non-abstract view of the model in a SAM.

PowerDesigner allows you to verify the validity of your models via the Model Check facility (press <F4> to run the model check). All of the checks listed for the CDM in Chapter 15 are useful for a LDM. For the LDM, the following additional checks are worth noting.

·         Detect inconsistencies between check parameters

·         Precision > maximum length

·         Undefined data type

·         Invalid data type

·         Existence of attributes

·         Existence of relationship or association link(s)

·         Redundant inheritance

·         Multiple inheritance

·         Parent of several inheritances

·         Detect differences between attribute and associated domain

·         Detect inconsistencies between check parameters

·         Precision > maximum length

·         Undefined data type

·         Invalid data type

·         'Many-many' relationships

·         Incomplete inheritance with ungenerated ancestor, which means that the ‘generate’ property for a super-type entity is not selected, and the sub-types are not a complete set. Generating the sub-type entities into a PDM will possibly result in missing data.

“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 LDM entities and relationships.

Make the LDM 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 LDM 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 LDM via the portal.

Create a new LDM called “Exercise 16”, containing the entities, attributes, and relationship from Figure 16.27.

Figure 16.27 LDM subset

The relationship states:

·         Each Office may be the location of one or many Employees.

·         Each Employee may reside in one Office.

Note the naming standard we are using for attributes – we don’t include the entity name in attribute names. The data element Employee First Name is represented by the attribute First Name in the entity Employee.

Take the LDM you created in the previous exercise.

You need to add the data element Office First Occupied Date to this model.

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