
h2(OCLInterpreterExample). OCL Interpreter Example

h3. Introduction

This example illustrates the usage of the generic OCL Parser API to parse and evaluate OCL query expressions and constraints within the SDK. It demonstrates how to author OCL expressions and evaluate them against elements of library model instances, or against Ecore and UML elements.  For Ecore and UML models, a further option of parsing (not evaluating) model-level (M1 in the OMG modeling stack) constraints is available.

h3. References

Please refer to the document "Object Constraint Language Examples Overview":ExamplesOverview for reviewing the library meta-model used as the basis for demonstrating the capabilities in this example.

h3. Description

This example plug-in is named @org.eclipse.emf.ocl.examples.interpreter@. This plug-in contributes the @OCL Interpreter@ menu to the library editor's main menu and context menu. The menu has one item:

* @Show Console@: Opens the interactive OCL console.

Please refer to the tutorial "OCL Interpreter Tutorial":#OCLInterpreterTutorial for reviewing the code samples within this example.

!{width:70%}images/3200-lib_editor_contrib.png(OCL Interpreter Example Contributions)!

The bottom field in the console accepts OCL expressions (comments supported). You can press *Enter* to evaluate on the currently selected element. You can press *Ctrl+Enter* or *Shift+Enter* to insert a newline. The top field shows the output and errors. The console can be cleared by the *Eraser* button and closed by the *X* button.

Because the @EXTLibrary@ model is based on the Ecore metamodel, ensure that the @Ecore@ metamodel is selected in the console's tool bar.  Also ensure that the @M2@ modeling level is selected, as @EXTLibrary@ is not a metamodel, so instances of it are not models.  Thus, the OCL expressions that
we create will target the Ecore meta-model, as the model of the EXTLibrary model.

Content-assist is automatically activated on typing any of "@.@", "@->@", "@::@", and "@^@".  Also, @Ctrl+Space@ can be used to invoke content-assist at any time.

!{width:70%}images/3200-lib_console.png(OCL Interactive Console)!

h3. Support for Ecore and UML Models

The OCL Console contributes an *OCL->Show OCL Console* menu action to the Ecore and UML editors (for @*.ecore@ and @*.uml@ models).  These actions automatically select the appropriate metamodel in the console.

For both Ecore and UML, parsing constraints at the @M1@ (model) level is supported.  This implements a scratch pad for developing OCL constraints in the context of:

* classifiers, for invariant constraints
* operations, for pre/post condition constraints and body expressions
* attributes, for initial-value and derivation constraints

The console infers the kind of constraint from the selected element; in the case of an operation, it assumes a post-condition constraint as these constraints support a superset of the syntax for pre-conditions and body expressions.

!{width:70%}images/3200-ecore_console.png(OCL Constraints for Ecore Model)!

The figure above shows the parsing of a derivation constraint on an Ecore property (an @EStructuralFeature@).

!{width:70%}images/3200-uml_console.png(OCL Constraints for UML Model)!

The figure above shows the parsing of an invariant constraint on a UML classifier (a @Class@).  Note that UML can model the @Job@ as an association class; a roughly equivalent Ecore model is more verbose.

h3. Example Code

Refer to the code in this example if you need to:
* parse, validate and evaluate OCL queries and constraints on EMF model elements
* implement content-assist for OCL constraints in your model editor

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