A Metamodeling Approach to Pattern-Based Model Refactoring

class implemented_by Image Display (applying the Bridge pattern) displayed_on Display ImageImpl1 Figure 1. An example of pattern-based model refactoring. ConcreteImpB ConcreteImpA Implementor RefinedAbstraction Abstraction implemented_by Figure 2. A diagram of the Bridge pattern. tion of the UML designs representing solutions of the pattern Transformation specification: a specification of problem-to-solution transformations Figure 3 presents an overview of our metamodeling approach to specifying transformations. The M2 level is an extension of the UML metamodel level that supports the definition of a transformation language. The M1 level is an extension of the UML model level that supports representation of model transformations. A model transformation at the M1 level transforms a source model to a target model. The M1 model transformations are characterized by a transformation specification at the M2 level that includes a pattern problem specification for the source models and a pattern solution specification for the target models. We can also view the transformation specification at M2 as defining a transformation language for the pattern, and the transformations at M1 as statements of the language. A UML model that conforms to a pattern problem or solution specification is said to be an instance of the specification. Similarly, a model transformation that conforms to a transformation specification is said to be an instance of the transformation specification. Pattern problem and pattern solution specifications characterize a subset of UML models characterized by the UML metamodel, so we can view the specifications as defining UML metamodel specializations. UML tool developers can embed patterns by appropriately specializing their representations of the UML metamodel. Figure 4 illustrates how we can represent the pattern solution specification for a simplified form of the Observer pattern as a specialized form of the UML metamodel. The Observer pattern specification characterizes UML class diagrams that model structural aspects of Observer pattern solutions. Each target class diagram characterized by the spec5 4 I E E E S O F T W A R E h t t p : / / c o m p u t e r. o r g / s o f t w a r e Pattern problem specification Transformation specification Pattern solution specification Source model Target model T1 Model transformation Instance-of dependency Instance-of dependency Instance-of dependency M2