As we saw in the
Parsing Constraints and Queries topic, the OCL parser provides an
OCLHelper
API for parsing constraints embedded in models. OCL also permits constraints
to be specified in a text document, as an adjunct to the model. In this case,
the concrete syntax for context declarations indicates the context of
constraints, equivalent to their placement in models.
As an example, consider the following Complete OCL document:
The Ecore binding provided an
OCLInput
class to supervise the OCL source text, and the result of parsing the document was a
List<Constraint>
. The Pivot binding uses an Xtext parser with a UML-aligned output. The input text is therefore specified by
a URI and loaded by the Xtext parser to create a Concrete Syntax Resource. This may then be converted to the Pivot Abstract Syntax Resource. The Abstract Syntax Resource has a conventional Model, Package, Class, Operation hierarchy in order to provide a coherent composition context for the Constraints.
The Concrete Syntax Resource created by the Xtext parser
comprises a CompleteOCLDocumentCS
containing a PackageDeclarationCS for
extlibrary
containing a ClassifierContextDeclCS for
Library
containing a DefCS
containing a DefOperationCS for
getBooks
and a SpecificationCS
and a ClassifierContextDeclCS for
Book
containing an InvCS for
unique_title
containing a SpecificationCS
each SpecificationCS contains the parsed OCL Expression tree.
The complementing Abstract Syntax Resource
comprises a Model with a
pivot:/..../extlibrary.ocl
URI
containing a Package named
extlibrary
containing a Class named
Library
containing an Operation named
getBooks
containing a body Constraint
and a Class named
Book
containing an invariant Constraint for
unique_title
The complementing Abstract Syntax Resource has the same structure as the complemented Resource
The complemented Abstract Syntax Resource
comprises a Model with a
pivot:/..../extlibrary.ecore
URI
containing a Package named
extlibrary
containing a Class named
Library
and a Class named
Book
There are therefore two Class objects named
Library
, one for each Resource. The objects are distinct in so far as they belong to different resources, which can be separately serialized, and in so far as they may appear distinct to OCL expressions that use reflective access. However they are logically merged and the
MetaModelManager
provides utility methods that allow the multiple objects to be accessed as a merged object.
Given the
URI
of an OCL document, simply ask an
OCL
to parse it:
The
OCL
returns the list of constraints if they were
successfully parsed. They are retained by the OCL (available via the
getConstraints()
method at any time), and in particular,
any definitions of additional operations or attributes are available for
subsequent constraint parsing. Any number of OCL documents may be parsed by
the same
OCL
instance, combined also with constraints
parsed by
OCLHelpers
. All of these constraints are
retained by the
OCL
environment.
The source for these examples may be found in the org.eclipse.ocl.examples.xtext.tests plugin in model/parsingDocumentsExample.ocl and in src/org/eclipse/ocl/examples/test/xtext/PivotDocumentationExamples.java.