Semantics of OCL specified with QVT

Abstract

The Object Constraint Language (OCL) has been for many years formalized both in its syntax and semantics in the language standard. While the official definition of OCL's syntax is already widely accepted and strictly supported by most OCL tools, there is no such agreement on OCL's semantics, yet. In this paper, we propose an approach based on metamodeling and model transformations for formalizing the semantics of OCL. Similarly to OCL's official semantics, our semantics formalizes the semantic domain of OCL, i.e. the possible values to which OCL expressions can evaluate, by a metamodel. Contrary to OCL's official semantics, the evaluation of OCL expressions is formalized in our approach by model transformations written in QVT. Thanks to the chosen format, our semantics definition for OCL can be automatically transformed into a tool, which evaluates OCL expressions in a given context. Our work on the formalization of OCL's semantics resulted also in the identification and better understanding of important semantic concepts, on which OCL relies. These insights are of great help when OCL has to be tailored as a constraint language of a given DSL. We show on an example, how the semantics of OCL has to be redefined in order to become a constraint language in a database domain.

Correctly defined concrete syntax

“…Figure 7 shows an alternative concrete syntax definition for the USE input files, which follows our approach. This 1 The grammar presented here is a simplified version and has dropped all elements not needed for our running example, e.g. operation declarations, specialization between classes, different kinds of associations (aggregation, composition), etc.…”

“…Unfortunately, there is no commonly agreed format for these two parts, yet. This paper is only concerned about the first missing part (concrete syntax definitions) and will ignore entirely the problem of how the semantics of modeling concepts can be formally defined (interested readers are referred to [1] for a complementary approach on defining semantics).…”

Mapping of Behavior Model using Model Driven Architecture

“…As [3] said there is already two approaches to describe OCL constraints semantics (like this constraint eval: CONSTRAINT x STATE → {true,false,undefined}), which can be defined either mathematically by using structural induction over CONSTRAINT (refer to [4]), or logically like using Isabelle/High-Order Logic (HOL).…”

“…Metamodels are already used to define abstract syntax with very expressive and easy to understand, it is already also used to define the semantics of class diagrams that technique is provided by OMG using Evaluation-Metaclasses [3], which this approach is provided using transformation rules written in QVT. Figure1 shows metamodel for OCL abstract syntax, and figure2 shows metamodel for the semantics of OCL.…”

Behavior, Time and Viewpoint Consistency: Three Challenges for MDE

“…There are also other graphical approaches, most of which are in turn based on graph grammars. Among them, we can find the visual representation of QVT [7] (where QVT is given in-place semantics) or the use of different (usually extended) UML diagrams [8,9]. These approaches do not use (so far) the concrete syntax of the DSL, but an object diagram-like structure.…”