Save OCL Constraints in the Profile Definition
Papyrus supports two alternative ways of validating whether constraints are respected by models. Both ways provide the option to augment the information presented to the user when a given constraint fails. The user is always presented a list of constraints that failed. While this is an important information, it is better to have a customized message describing what is wrong. It's also useful to specify the severity, in particular, whether a constraint violation is an error or warning.
To augment the default constraint failure information you can either generate the constraints directly into the profile definition or generate a plugin that embeds the constraints. Both approaches are described below.
Constraints written in OCL within a UML profile can be generated into the definition of the profile. The constraint definition is taken into account during the validation of models that have applied the profile. This method is only applicable for OCL constraints.
How to embed the constraints definitions into a UML Profile:
The OCL pivot delegate supports a specific way to define a customized message and severity in the OCL constraint: The constraint needs to be written in form of a tuple, as shown here for an example.
Tuple{
status=base_Class.isActive,
message='\'' + base_Class.name + '\' is not active',
severity=-5
}.status
The original constraint expression is defined in the status field of the tuple, as well as the message and severity fields. Whereas only the status field is returned during evaluation, OCL evaluation with the Pivot delegate will also evaluate the custom message and severity.
Please note that this is just a different way to write OCL constraints, they are put into the profile definition in the same way as described above. At the moment, there is no specific support in Papyrus to facilitate entering OCL expressions in this way. Since the whole tuple is a "normal" OCL expression, syntax validation and completion is supported by the xtext based expression editor. But it is currently not clear whether Papyrus will 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.
If you only deal with OCL constraints, this method is simple and straightforward. But it is not possible to select whether constraints defined in this way are included for validation or not (they are always included).
Users can generate a plugin from a profile that embeds the constraints, which are expressed either in OCL or Java. OCL constraints are embedded into the plugin.xml while Java constraints can directly be compiled into code. This is supported by the EMF validation framework.
CAVEAT: The validation of OCL rules within a plugin is a rather old mechanism. It does not take the user preference of an OCL validation delegate into account. Therefore, validation is done with the classical LPG mechanism whereas the constraint editor within Papyrus validates the constraint itself (not whether other parts of the model respect the constraint) using the Pivot OCL mechanism. In particular, the qualified name of UML meta classes in LPG must start with uml:: whereas Pivot requires UML:: (upper case). In the future Papyrus will offer a way to ensure that the Pivot will be used for OCL contraints within plugins.
Help->Install New Software, select Papyrus update site, deselect "group items by category" and search for DSML.
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 profiles that adds domain specific concepts to UML.
The additional profile enables a specification of the following properties:
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:
Please note that the additional constraint information is only taken in to account if you generate a plugin embedding the constraints into the plugin.xml, as discussed above.
Help->Install New Software, select Papyrus update site, deselect "group items by category" and search for DSML
This method is a bit more complicated than the first, but also more powerful. It works for both OCL and Java. The constraints are grouped in a category that can be included in the validation or not. A message and severity specified via the DSML validation profile is taken into account. It is also possible to distinguish between Live and Batch constraints. Note that this approach is currently of limited use in the case of OCL constraints as different OCL backends are used during constraint definition and validation.
This section contains information about the code in the generated plugin. It is intended for readers that want to understand how the generated plugin works.
The EMF validation framework supports constraints by means of a suitable definition in the plugin.xml file that embeds OCL or Java constraints, 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>
Constraint 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>
The generator creates a selector for each context element (typically a stereotype). The selector checks the element to be validated and selects those typed with the context element or a sub-types thereof. The constraint binding associates a list of constraints with the selector: those that share the same context element.