(Soden & Eichler, 2009) discusses the need of extending the Eclipse Modeling Project under which EMF (based on MOF) is used to define Domain Specific Languages (DSL) and GMF to define Graphical Model Editors and Xtext to define Human Understandable Textual Notations (HUTN) for a defined DSL with a Model Execution Framework (MXF) that allows for the declarative specification of a model execution and simulation.

The idea is to extend an abstract syntax, that defines a Domain Specific Language (DSL) – for example a finite state machine language – with a model that describes runtime instances of the model (including state, counter, … ) plus a declarative (in this case even graphical) model for the behavior of the model simulation.

What I like in the idea is the thrive to make the DSL architect more productive in his work by relieving his duty to implement a model interpreter or model to code translator, if he invents a new DSL. By this, he can write a new DSL (like for example BPMN 2.0) and would be able to simulate the behavior of the execution semantics without implementation work – just by declarative modeling. That is the promise of the approach.

One could discuss, if the chosen Language MAction is the best way to describe model execution semantics, but at least it has to be taken serious. For me this is an interesting DSL prototyping environment. If one looks at model execution at runtime, I do not think that the Eclipse Environment is the right architecture for this. But it is a start – as I said – for DSL Prototyping. Other points that should be discussed in the future in my opinion are:

• Runtime Optimization for the Model by adding shortcuts in the Runtime Model
• Modeling of big examples (like BPMN 2.0) with the new language
• Evaluation of different ways of describing the Model Execution Semantics

References

Soden, M., & Eichler, H. (2009). Towards a Model Execution Framework for Eclipse. First European Workshop on Behaviour Modelling in Model Driven Architecture (BM-MDA) (S. 57-71). Amsterdam, The Netherlands: Centre for Telematics and Information Technology Workshop Proceedings.

In the same workshop as mentioned before there was the presentation of (McNeile & Roubtsova, 2009).

UML State Machines were discussed for the purpose of behavior modeling. It was rightly pointed out, that they have some severe weaknesses.

One weakness is that events trigger transitions, but if there is no transition with the event, the event is not inhibited. It just happens without any result.

A second weakness is the possibility of a state explosion in real scenarios. This can – in my opinion however – be addressed with state regions (see UML).

Another weakness is the lack of composition capability – i.e. the possibility to add a model part that does not modify another model part but has an effect.

I agree to these observations.

Furthermore It was distinguished between states that are actively set (like active or closed) and those which are calculated and whose transition are done by change of input values (like overdrawn or in credit with a bank account). While I see these differences as well, in my opinion they are not so strict. There are also cases where there is a state, that is changed actively (not completed) but the result state is calculated (partially completed, fully completed). For this case it was not taken account for.

As a solution it was proposed that protocol machines are constructed, that are able to Allow an event or Refuse or Ignore. While I can understand for what Allow and Refuse is needed (i.e. Buttons on a Screen) I see no direct use case for Ignore.

Also it was proposed a composition mechanism that provides for adding behavior to a model without modifying it. While I think this is pointing into the right direction and this should be achieved, I have doubts if the way that was presented was the solution. There were some ambiguities in the proposal – especially with regards to the question what the absence of a transition within a certain region really means (Refusal?)

All in all for me it was one of the most interesting presentations going into a promising direction.

References

McNeile, A., & Roubtsova, E. (2009). Composition Semantics for Executable and Evolvable Behavioral Modeling in MDA. First European Workshop on Behaviour Modelling in Model Driven Architecture (BM-MDA) (S. 41-56). Amsterdam, The Netherlands: Centre for Telematics and Information Technology Workshop Proceedings.

Continuing my thoughts about the MDA Conference I want to make some remarks about (Kalnis, Celms, Kalnina, & Sostaks, 2009).

It was rightly stated in the presentation, that UML sequence diagrams are insufficient to model behavior and that a new kind of modeling method is needed. Also the lack of a modeling method for operations of a class was obvious – nobody knows in which sequence they have to be called – if not prose does describe it. Therefore a new modeling method was proposed, that displays classes as swim lanes containing the operation definitions of the class as nested activities containing actions. In this “action language” sequences can be expressed by arrows between actions of one swim lane and other swim lanes.

In my opinion this idea points into the right direction. Actions / operations must be set into relation with regards to their mutual constraints and a simple graphical notation for this is needed.

I did not understand however why it is necessary to distinguish between operations and actions, because in my opinion the actions in this method reveals details of the inner structure of the operations, which is in my opinion not relevant. Furthermore in my opinion the flow based modeling (arrows) leads into a model explosion, if big examples (business use cases) are modeled.

In my opinion the suggestion of (Engels, 2009) was more appropriate to the task in this aspect.

References

Engels, G. (2009). Keynote: Automatic generation of behavioral code – too ambitious or even unwanted? In M. Aksit, E. Kindler, A. McNeile, & E. Roubtsova (Hrsg.), First European Workshop on Behaviour Modelling in Model Driven Architecture (BM-MDA). Amsterdam, The Netherlands: Centre for Telematics and Information Technology Workshop Proceedings.

Kalnis, A., Celms, E., Kalnina, E., & Sostaks, A. (2009). Behaviour Modelling Notation for Information Systems Design. In M. Aksit, E. Kindler, A. McNeile, & E. Roubtsova (Ed.), First European Workshop on Behaviour Modelling in Model Driven Architecture (BM-MDA) (pp. 29-40). Amsterdam, The Netherlands: Centre for Telematics and Information Technology Workshop Proceedings.