A Graphical Notation to Specify Model Queries for MDA Transformations on UML Models

Specifying queries on models is a prerequisite to model transformations in the MDA because queries select the model elements that are the source of transformations. Current responses to OMG's MOF 2.0 QVT RFP mostly propose to use (and/or extend) OCL 2.0 as specification language for queries. In this paper, we demonstrate that using textual notations (like OCL) quickly leads to complex query statements even for simple queries. In order to overcome this handicap, we present a graphical notation based on the UML that facilitates comprehension of query statements as well as estimation of the (ultimately) selected model elements. We advocate that queries should be specified in terms of user model entities and user model properties (rather than meta-model entities and meta-model properties) for the sake of feasibility and comprehensibility to the user.