Example: Creating Robustness Diagram Extensions

In this example, we will recreate the Robustness extension file delivered with PowerDesigner to extend the OOM communication diagram to enable robustness analysis. Robustness diagrams sit between use case and sequence diagram analysis, and allow you to bridge the gap between what the system has to do, and how it is actually going to accomplish it.

In order to support the robustness diagram, we will need to define new objects by applying stereotypes to a metaclass, specify custom tools and symbols for them, as well as defining custom checks for instance links and producing a file to output a description of messages exchanged between objects.

Creating the robustness extensions will enable us to verify use cases like the following, which represents a basic Web transaction:

A customer wants to know the value of his stocks in order to decide to sell or not, and sends a stock value query from his Internet Browser, which is transferred from his browser to the database server via the application server.

• Creating a New Extension File in your Model
  The first step in defining extensions, is to create an extension file (.xem) to keep them in. To begin this process, you should create or open an OOM.
• Creating New Objects with Stereotypes
  To implement robustness analysis in PowerDesigner, we need to create three new types of objects (boundary, entity, and control objects), which we will define in the Profile category by extending the UMLObject metaclass through stereotypes.
• Specifying Custom Symbols for Robustness Objects
  We will specify diagram symbols for each of our new robustness diagram objects by adding custom symbols to our new stereotypes.
• Creating Custom Checks on Instance Links
  We will now create three custom checks on the instance links that will connect the various robustness objects. These checks, which are written in VB, do not prevent users from creating diagrams not supported by the robustness methodology, but define rules that will be verified by the Check Model function.
• Defining Templates to Extract Message Descriptions
  We are going to generate a textual description of the messages in the diagram, giving for each message, the names of the sender, message, and receiver. To do so, we will need to define PowerDesigner Generation Template Language (GTL) templates to extract the information and a generated file to contain and display the extracted information.
• Creating a Generated File for the Message Information
  Having created templates to extract information about the messages in the model, we need to create a generated file to contain and display them on the Preview tab of the diagram property sheet. We will define the file on the BasePackage metaclass, which is the common class for all packages and models, and will have it loop through all the communication diagrams in the model to evaluate the template description defined on the CommunicationDiagram metaclass.
• Testing the Robustness Extensions
  To test the extensions we have created, we will create a small robustness diagram to analyze our use case.