Revision as of 11:29, 10 June 2014

Refine constraint validation

The information that a constraint has been violated is important, but a user typically wants to see a useful message what is wrong instead of that a certain constraint has been violated. Papyrus supports a UML profile that enables a developer to refine how constraints are violated. This profile is called Domain Specific Modeling Language (DSML), since it is often used in the context of constraints that are part of a profile that adds domain specific concepts to UML.

The additional profile enables a more precise specification of the following properties:

• Mode: Defines if the validation of the constraint is done in “batch” or “live” mode
• Severity: Defines the severity of the constraint violation. It can be one of INFORMATION, WARNING or ERROR. The latter is the default severity (if none is specified). The CANCEL severity should be used with caution, as it causes the validation operation to be interrupted, possibly resulting in the loss of valuable diagnostic information from other constraints.
• Message: Defines the message that will be displayed if the constraint is violated
• Description: Provides a description of the constraint
• Enabled by default: Defined if this constraint should be enabled by default or not

The attributes of the profile correspond quite closely to the possibilities that the EMF validation framework offers when constraints are specified in the plugin.xml of a profile.

Advanced users can also define:

• Status code: The plug-in unique status code, useful for logging.
• Target: The element to be validated

Please note that the additional constraint information via the profile is only taken into account, if you plan to generate a plugin embedded the constraints into the plugin.xml, as shown later.

How to apply the DSML validation profile

• 1. Select the UML Profile element in the Model Explorer

• 2. Select the Profile tab in the Properties View

• 3. Click on the "Apply registered profile" button

• 4. Select the "DSML Validation" profile

• 5. Select the UML Constraint element in the Model Explorer or diagram

• 6. Select the Profile tab of the Properties View

• 7. Click on the "Apply stereotype" button

• 8. Select the ValidationRule stereotype

• 9. Edit the stereotype properties to define information about the behavior of the validation

Generation from Constraints

A plugin can contain a set of validation rules that are expressed either in OCL or Java. EMF validation supports this by means of a suitable definition in the plugin.xml file that embeds OCL rules, as shown here (example taken from the OCL tutorial).

First define a category

<extension point="org.eclipse.emf.validation.constraintProviders">
   <category
         name="Your category" id="emf-validation-example/ocl">
      Category description
   </category>

Then define constraints within the category

   <constraint lang="OCL" severity="WARNING" mode="Batch" name="An example" id="example1" statusCode="101">
      <description>Describe it</description>
      <message>Write the message</message>
      <target class="Writer"/>
      <![CDATA[
         self.books->collect(b : Book | b.category)->asSet()->size() <= 2
      ]]>
   </constraint>

Constraints validation needs to be done on the context element. Therefore, the plug-in definition needs to associate constraints with the elements that should be validated. This is called constraint binding. The following snipped shows an example of such a binding.

  <extension point="org.eclipse.emf.validation.constraintBindings">
      <clientContext id="MyContextID">
         <selector class=myplugin.selectors.ConstraintSelector"/>
      </clientContext>
      <binding context="MyContextID">
         <constraint ref="myplugin.example1"/>
      </binding>

Papyrus supports the generation of a generated plug-in from a plugin, in particular for the case of stereotypes as context elements.

OCL constraints can be embedded into the profile definition and are validated without a dedicated plugin. Thus, if you only deal with OCL constraints, it is not necessary to create such a plugin. It may still be interesting, since the constraints defined in the generated plugin are grouped in a category. In addition, a message and severity specified via the DSML validation profile is taken into account.

Do one of the following:

Generate constraints directly into the profile definition

Constraints written in OCL within a UML Profile can be generated into the definition of the profile and read during the validation of the model to which the profile is applied.

How to embed the constraint definitions into a UML Profile:

• 1. Save the profile
• 2. Papyrus asks to you if "Would you like to define it" (the profile), select Yes
• 3. Ensure "Save OCL constraint in the definition" is selected (the box is checked by default in later versions of Papyrus)
  

Note that it is possible to control the message and severity using this method by writing the OCL constraint as a tuple, as shown here

Tuple{
  status=base_Class.isActive,
  message='\'' + base_Class.name + '\' is not active',
  severity=-5
}.status

It is currently not clear whether Papyrus should offer a way to edit this tuple in a user friendly way, e.g. by synchronizing message and severity with information from the DSML stereotype and only showing the original OCL constraint to the user.

Generate constraints as EMF validation plugins

The user can generate a plugin that wraps constraints and can be used in the EMF plugin validation.
The constraint can be generated in Java code, or directly from OCL.

How to embed the generate constraints into a plugin:

• 1. Select the UML Profile element in the Model Explorer
• 2. Right click UML Profile element
• 3. Select "create validation plugin for this DSML" from the context menu
• 4. Enter a Project name when prompted by the wizard
• 5. Complete the wizard and select Finish
• 6. Install or deploy the plugin with associated profile

Please note that you should not embed constraints into the profile, if you plan to generate a plugin.