3.1 OMG Standards

The MDA is defined and trademarked by the OMG. We therefore first take a look at the OMG standards that play a role within the MDA framework.

3.1.1 OMG Languages

The OMG defines a number of modeling languages that are suitable to write either PIMs or PSMs. The most well-known language is UML. This is the most widely used modeling language.

The Object Constraint Language (OCL) is a query and expression language for UML, which is an integral part of the UML standard. The term "Constraint" in the name is an unfortunate leftover from the time when OCL was used to specify only constraints to UML models. Currently, OCL is a full query language, comparable to SQL in its expressive power.

The Action Semantics (AS) for UML defines the semantics of behavioral models in UML. Unfortunately, it defines the behavior at a low-level foundation. Therefore, it is not directly suitable for writing PIMs. It lacks the higher level of abstraction that is necessary. The AS is not a language that can be used directly by a modeler, because it does not define a concrete syntax; you cannot write down anything at all in a standardized way.

UML includes a profile mechanism that enables us to define languages derived from the UML language. The language defined in the profile is a subset of UML with additional constraints and suitable for a specific use. It uses the UML diagrammatic notation and OCL textual queries, and looks like UML. Many such profiles are standardized by the OMG; others are not standardized, but publicly available. Official OMG profiles include the CORBA Profile, the Enterprise Distributed Object Computing (EDOC) Profile, the Enterprise Application Integration (EAI) Profile, and the Scheduling, Performance, and Time Profile. More profiles are being developed and will be standardized in the coming years . Profiles are usually suitable for writing PSMs.

The UML/EJB Mapping Specification (EJB01) is an example of a profile that is standardized through the Java Community Process. Several profiles for other programming languages, like Java, C#, and so on, are defined by individual organizations and tool vendors .

Another language that is defined by the OMG is the Common Warehouse Metamodel (CWM). This is a language specifically designed to model data mining and related systems.

Chapter 11 describes the various OMG languages and their role in MDA in more detail.

3.1.2 OMG Language and Transformation Definitions

Languages used within the MDA need to have formal definitions so that tools will be able to automatically transform the models written in those languages. All of the languages standardized by the OMG have such a formal definition. The OMG has a special language called the Meta Object Facility (MOF), which is used to define all other languages. This ensures that tools are able to read and write all languages standardized by the OMG.

The transformation definitions used in the MDA framework are currently defined in a completely nonstandardized way. To allow standardization of these transformation definitions, the OMG is currently working on a standard language to write transformation definitions. This standard is called QVT, which stands for Query, Views, and Transformations. At the time of writing, the Request for Proposals (RfP) for QVT has been published. QVT is still being worked on by OMG members so we don't yet know exactly how the finished specification will look.