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The architect selects these operators from a predefined palette and specifies the parameters necessary to apply them to the evolving model. As the architect does so, the effects of the operators are displayed.

Once the definition of the operators making up the transition is finished, the architect exits transition specification mode.

The architect continues specifying transitions as in step 3 until all transitions in the graph have been specified. If a path fails to satisfy any of the constraints, the user is notified of the violation and given the opportunity to correct it. Finally, the architect can run a set of predefined evaluation functions, which provide quantitative assessments of each valid path. The architect is now equipped to make an informed decision about the optimal evolution path. The most basic help with an essay and limited is by defining UML profiles.

A much richer extension mechanism is the MagicDraw Macro Engine, which I used in our JPL case study to generate an evolution graph, as described in chapter 4. Finally, the most powerful means of extension that MagicDraw provides are plug-ins, the approach we used to develop this prototype.

Development of the prototype proceeded in stages, each designed to result in a particular unit of functionality.

This staged development approach allowed us to familiarize ourselves with the relevant portions of the OpenAPI rapidly.

The development stages were: Feature 1: Manipulation of the evolution model. Screenshots of feature prototype 3, the operator palette interface. At left, the user selects an operator from the palette. This prototype was similar in function to the transformation macro that was used to define evolution operators in the JPL case study.

Here, however, this was accomplished by means of a plug-in rather than a macro. The second feature prototype was intended to demonstrate basic reasoning about an evolution model. Given a Magic- Draw model of an evolution graph, this feature prototype would analyze the model and identify all the evolution paths in the graph. Feature 3: Interface for applying evolution operators.

The third feature prototype was thus an interface for applying an evolution operator (Fig. To apply an operator, the user firsts select an operator from a palette, then specifies any required parameters.

In this stage, we developed a parser for a highly simplified version of our operator specification language. We considered several mechanisms for storing metadata. The most principled approach would have been to develop a UML profile for the purpose paper writers online of representing architecture evolution graphs. However, while elegant, this solution would have taken too long to implement given the limited time available. For this feature, we adopted the cruder but more expedient approach of storing metadata in existing fields intended for other purposes. For example, when a user applies an operator that introduces a new component, how should we position that component in any diagrams that are associated with the new state? We considered a number of possible approaches, including making use of the layout algorithms built into MagicDraw, requiring the user to specify the placement of new presentation elements, or even developing layout algorithms of our own. Evolution path constraints, like operators, are defined in a configuration file that is read by our plug-in when it is loaded. The constraints are written in a simplified subset of our constraint specification language.

The final feature prototype comprised a parser and interpreter for this language. The final phase of development was an integration phase aimed at tying these features together into a unified tool. For the most part, the project proceeded as expected. However, there were a number of unexpected challenges.

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First, the MagicDraw API turned out to be less flexible than paper writers online we had hoped, making it difficult or impossible to implement several of the features that we had envisioned. For example, the API does not provide much flexibility for plug-in developers to overhaul or replace the default user interface, which made implementing the kind of work flow we had envisioned impractical. In addition to limitations in API functionality, we also experienced problems pertaining to API discoverability. Much of this was due simply to the significant size of the MagicDraw OpenAPI.

With such a large API, it is difficult for a small team of part-time developers to learn it quickly. Thus, it was often difficult to find the features we needed, or even to know which features the API supported. These delays (along with technical difficulties in the project set-up phase) slowed our progress significantly. Although we completed all planned feature prototypes, many of them were not as fully fleshed out as we had anticipated, as mentioned 123 6 Tooling above. This also left insufficient time for the integration phase to be satisfactorily completed. Understanding the kinds of variation that the framework supports Plug-ins are, by nature, subject to the limitations of the frameworks they are based on. In this project, we found that some of the features we wished to implement (e. For a software architecture evolution plug-in, one especially important kind of variation is variation in the user interface, which I discuss next. For an architecture evolution plug-in to be usable, it is essential that significant modifications to the basic user interface of the modeling tool be possible. We found this to be impractical with the MagicDraw OpenAPI. Ideally, we might hope that paper writers online the architecture modeling platform on which our plug-in is based would provide advanced diagram layout features. The characteristics of the MagicDraw API that presented challenges for us—the rigidity of its user interface, the difficulty of prohibiting user actions that cause model inconsistencies, support for advanced diagram layout features—should certainly not be seen as failings or defects in MagicDraw. Rather, they arise from deliberate (and not unreasonable) API design choices that the developers of MagicDraw made in order to better support the core features that they wished to expose. But they do present limitations in the context of an architecture evolution modeling plug-in, and such limitations should be carefully considered by developers of any such plug-in. I suspect that most architecture modeling tools will tend to share many of these same limitations. Thus, many of the challenges we encountered are likely to pose difficulties for anyone developing an architecture evolution tool as a plug-in to an existing architecture modeling tool. If that is the case, these challenges may be fairly fundamental ones that future developers of architecture evolution tools will be forced to confront (or they will have to take great care in selecting an architecture modeling tool that is closely aligned with the necessary requirements). Of course, an alternative is to develop an architecture evolution tool from the ground up, without basing it on an existing architecture modeling framework, but this would involve forgoing the important benefits that a plug-in based approach provides, such as the ability to leverage the existing architecture modeling facilities that such a framework provides and the greater usability that results from plugging into a modeling framework with which users are already familiar.

Our approach to architecture evolution modeling is designed to lend itself to tool support, and many of the core features of our approach appear to be implementable in a reasonably straightforward way.

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