Extension Files

Extensions files (*.xem) provide means for customizing and extending PowerDesigner metaclasses, parameters and generation. You can use extensions to define additional properties for existing object types or entirely new kinds of objects, to modify the PowerDesigner interface (reorganizing and adding property sheet tabs, Toolbox tools and menu items), and to define additional generation targets and options.

PowerDesigner provides a number of predefined extension files and you can also create your own. Each extension file contains two first-level categories:

Generation - used to develop or complement the default PowerDesigner object generation (for BPM, OOM, and XSM models) or for separate generation. For more information, see Generation Category.
Profile - a UML extension mechanism, which is used for extending a metamodel for a particular target. Profiles are used in PowerDesigner for adding additional metadata to objects and creating new kinds of links between them, sub-dividing object types (via stereotypes and criteria), customizing symbols, menus, and forms, and modifying generation output. For example:
- The Java 5.0 object language resource file - extends the Component metaclass via several levels of criteria to model various forms of EJBs.
- The BPEL4WS 1.1 process language resource file - extends the Event metaclass through stereotypes to model Compensation, Fault, and Timer events.
- The MSSQLSRV2005 DBMS resource file - uses stereotyped extended objects in order to model aggregates, assemblies, and other SQL Server-specific objects.
You can extend the metamodel in the following ways:
- Add or sub-classify new kinds of objects:
  - Metaclasses – drawn from the metamodel as a basis for extension.
  - Stereotypes [for metaclasses and stereotypes only] – to sub-classify objects.
  - Criteria – to evaluate conditions to sub-classify objects.
  - Extended objects, sub-objects, and links – to create new kinds of objects.
- Provide new ways of viewing connections between objects:
  - Dependency matrices – to show connections between two types of objects.
  - Extended collections and compositions – to enable manual linking between objects.
  - Calculated collections – to automate linking between objects.
- Add new properties to objects and display them:
  - Extended attributes – to provide extra metadata.
  - Forms – to display custom property tabs or dialog boxes.
  - Custom symbols – to help you visually distinguish objects.
- Add constraints and validation rules to objects:
  - Custom checks – to provide data testing.
  - Event handlers – to invoke methods when triggered by an event.
- Execute commands on objects:
  - Methods – to be invoked by other profile extensions such as menus and form buttons (written in VBScript).
  - Menus [for metaclasses and stereotypes only] – to customize PowerDesigner menus.
- Generate objects in new ways:
  - Templates and generated files – to customize generation.
  - Transformations and Transformation profiles – to automate changes to objects at generation or on demand.

You can review and edit the profile in a resource file by opening it in the Resource Editor and expanding the top-level Profile category. You can add extensions to a metaclass (a type of object, such as Class in an OOM or Table in a PDM), or to a stereotype or criterion, which has previously been defined on a metaclass:

In the example above:

Class is a metaclass. Metaclasses are drawn from the PowerDesigner metamodel, and always appear at the top level, directly beneath the Profile category
MyCriterion is a criterion that refines the Class metaclass. Those classes that meet the criterion can be presented and processed differently from other classes.
MyStereotype is a stereotype that refines the Class metaclass. Those classes that bear the MyStereotype stereotype can be presented and processed differently from other classes.
AnotherCriterion is a criterion that refines further those classes that bear the MyStereotype stereotype. Classes bearing the stereotype AND meeting the criterion can be presented and processed differently from those that merely bear the stereotype.

Extensions are inherited, so that any extensions made to a metaclass are available to its stereotyped children, and those that are subject to criteria.

Thus, in the example above, classes that bear the MyStereotype stereotype have available the Attribute_5 extended attribute, and those that bear this stereotype AND meet AnotherCriterion have Attribute_4 and Attribute_5 available.

Note: Since you can attach several resource files to a model (for example, a target language and one or more extension files) you can create conflicts, where multiple extensions with identical names (for example, two different stereotype definitions) are defined on the same metaclass in separate resource files. In case of such conflicts, the extension file extension usually prevails. When two XEMs are in conflict, priority is given to the one highest in the list.

Creating an Extension File
You can create an extension file from the list of extension files or directly embedded in your model.
Attaching Extensions to a Model
Extensions can be in independent *.xem files that are attached to models or can be embedded in model files. Independent extension files can be referenced by multiple models, and any changes made to such a file are shared by all models that attach it. Changes made to extensions embedded in a model file affect only that model.
Exporting an Embedded Extension File for Sharing
If you export an XEM created in a model, it becomes available in the List of Extensions, and can be shared with other models. When you export an XEM, the original remains embedded in the model.
Extension Properties
All extension filess have the same basic category structure.
Example: Adding a New Attribute from a Property Sheet
In this example, we will quickly add a new attribute directly from the property sheet of an object. PowerDesigner will manage the creation of the extension file and creation of all the necessary extensions.
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.
Extending Generation and Creating Separate Generation Targets
Extensions can be used to extend generation and create new generation targets.
Metaclasses (Profile)
Metaclasses are classes drawn from the PowerDesigner metamodel, and appear at the top level of the Profile category. You add a metaclass to a profile when you want to extend it.
Stereotypes (Profile)
Stereotypes are a per-instance extension mechanism. When a stereotype is applied to a metaclass instance (by selecting it in the Stereotype field of the object's property sheet), any extensions that you add to the stereotype are then applied to the instance.
Criteria (Profile)
You can control the treatment of metaclass instances based on whether they conform to one or more criteria. Whereas you can apply only one stereotype to a metaclass instance, you can test the instance against multiple forms of criteria.
Extended Objects, Sub-Objects, and Links (Profile)
Extended objects, sub-objects, and links are special metaclasses that are designed to allow you to add completely new types of objects to your models, rather than basing them on existing PowerDesigner objects.
Dependency Matrices (Profile)
Dependency matrices allow you to review and create links between any kind of objects. You specify one metaclass for the matrix rows, and the same or another metaclass for the columns. The contents of the cells are then calculated from a collection or link object.
Extended Attributes (Profile)
Extended attributes allow you to define additional metadata for your objects.
Extended Collections and Compositions (Profile)
An extended collection allows you to associate multiple instances of one metaclass with an instance of another.
Calculated Collections (Profile)
You define a calculated collection on a metaclass, stereotype, or criterion, when you need to display a list of associated objects with a user-defined semantic.
Forms (Profile)
You can use forms to create new property sheet tabs or to replace existing tab, or to create dialog boxes that are launched from menus or by clicking on buttons in your property sheet tabs. Building a new form is fast and easy, using the form tools in the resource editor.
Custom Symbols (Profile)
A custom symbol allows you to modify the appearance of instances of the metaclass, stereotype, or criterion.
Custom Checks (Profile)
Custom checks are model checks, written in VBScript, which enable you to verify that your model objects are well-defined. Custom checks are listed with standard model checks in the Check Model Parameters dialog box.
Event Handlers (Profile)
An event handler can automatically launch a VBScript when an event occurs on an object. You can associate an event handler with a metaclass or a stereotype; criteria do not support event handlers.
Methods (Profile)
Methods allow you to perform actions on objects.
Menus (Profile)
You can add menus in the PowerDesigner interface and fill them with commands that call method or transformations.
Templates and Generated Files (Profile)
You can define templates and generated files for metaclasses, stereotypes, and criteria. If a template applies to all metaclasses, then you should create it in the Shared category.
Transformations and Transformation Profiles (Profile)
A transformation defines a set of actions to be executed during generation or upon request. You define a transformation in the profile category of an extension on a metaclass or a stereotype or other criteria.