Jean-Marc Jézéquel

Making components contract aware

Components have long promised to encapsulate data and programs into a box that operates predictably without requiring that users know the specifics of how it does so. Many advocates have predicted that components will bring about widespread software reuse, spawning a market for components usable with such mainstream software buses as the Common Object Request Broker Architecture (CORBA) and the Distributed Component Object Model (DCOM). In the Windows world, at least, this prediction is becoming a reality. Yet recent reports indicate mixed results when using and reusing components in mission-critical settings. Such results raise disturbing questions. How can you trust a component? What if the component behaves unexpectedly, either because it is faulty or simply because you misused it? Before we can trust a component in mission-critical applications, we must be able to determine, reliably and in advance, how it will behave. In this article the authors define a general model of sofware contracts and show how existing mechanisms could be used to turn traditional components into contract-aware ones.

Weaving executability into object-oriented meta-languages

Nowadays, object-oriented meta-languages such as MOF (Meta-Object Facility) are increasingly used to specify domain-specific languages in the model-driven engineering community. However, these meta-languages focus on structural specifications and have no built-in support for specifications of operational semantics. In this paper we explore the idea of using aspect-oriented modeling to add precise action specifications with static type checking and genericity at the meta level, and examine related issues and possible solutions. We believe that such a combination would bring significant benefits to the community, such as the specification, simulation and testing of operational semantics of metamodels. We present requirements for such statically-typed meta-languages and rationales for the aforementioned benefits.

Models@ Run.time to Support Dynamic Adaptation

Todays society increasingly depends on software systems deployed in large companies, banks, airports, and so on. These systems must be available 24/7 and continuously adapt to varying environmental conditions and requirements. Such dynamically adaptive systems exhibit degrees of variability that depend on user needs and runtime fluctuations in their contexts. The paper presents an approach for specifying and executing dynamically adaptive software systems that combines model-driven and aspect-oriented techniques to help engineers tame the complexity of such systems while offering a high degree of automation and validation.

Taming Dynamically Adaptive Systems using models and aspects

Since software systems need to be continuously available under varying conditions, their ability to evolve at runtime is increasingly seen as one key issue. Modern programming frameworks already provide support for dynamic adaptations. However the high-variability of features in Dynamic Adaptive Systems (DAS) introduces an explosion of possible runtime system configurations (often called modes) and mode transitions. Designing these configurations and their transitions is tedious and error-prone, making the system feature evolution difficult. While Aspect-Oriented Modeling (AOM) was introduced to improve the modularity of software, this paper presents how an AOM approach can be used to tame the combinatorial explosion of DAS modes. Using AOM techniques, we derive a wide range of modes by weaving aspects into an explicit model reflecting the runtime system. We use these generated modes to automatically adapt the system. We validate our approach on an adaptive middleware for home-automation currently deployed in Rennes metropolis.

On model typing

Where object-oriented languages deal with objects as described by classes, model-driven development uses models, as graphs of interconnected objects, described by metamodels. A number of new languages have been and continue to be developed for this model-based paradigm, both for model transformation and for general programming using models. Many of these use single-object approaches to typing, derived from solutions found in object-oriented systems, while others use metamodels as model types, but without a clear notion of polymorphism. Both of these approaches lead to brittle and overly restrictive reuse characteristics. In this paper we propose a simple extension to object-oriented typing to better cater for a model-oriented context, including a simple strategy for typing models as a collection of interconnected objects. We suggest extensions to existing type system formalisms to support these concepts and their manipulation. Using a simple example we show how this extended approach permits more flexible reuse, while preserving type safety.

Semantic-based weaving of scenarios

The notion of aspect looks promising for handling cross-cutting concerns earlier in the software life-cycle, up from programming to design, analysis and even requirements. Support for aspects is thus now raising interest also at the modeling level, including with behavioral modeling languages such as scenarios. With this kind of modeling languages, even if aspect weaving can be performed at the abstract syntax level, a weaving at the semantics level seems a far more appealing and powerful mechanism. In this paper we present a semantic-based aspect weaving algorithm for Hierarchical Message Sequence Charts (HMSCs). The algorithm proposed uses a set of transformations that take into account the compositional semantics of HMSCs to weave an initial HMSC and a behavioral aspect expressed with scenarios.

An Aspect-Oriented and Model-Driven Approach for Managing Dynamic Variability

Constructing and executing distributed systems that can adapt to their operating context in order to sustain provided services and the service qualities are complex tasks. Managing adaptation of multiple, interacting services is particularly difficult since these services tend to be distributed across the system, interdependent and sometimes tangled with other services. Furthermore, the exponential growth of the number of potential system configurations derived from the variabilities of each service need to be handled. Current practices of writing low-level reconfiguration scripts as part of the system code to handle run time adaptation are both error prone and time consuming and make adaptive systems difficult to validate and evolve. In this paper, we propose to combine model driven and aspect oriented techniques to better cope with the complexities of adaptive systems construction and execution, and to handle the problem of exponential growth of the number of possible configurations. Combining these techniques allows us to use high level domain abstractions, simplify the representation of variants and limit the problem pertaining to the combinatorial explosion of possible configurations. In our approach we also use models at runtime to generate the adaptation logic by comparing the current configuration of the system to a composed model representing the configuration we want to reach.

Meta-model Pruning

Large and complex meta-models such as those of Uml and its profiles are growing due to modelling and inter-operability needs of numerous stakeholders. The complexity of such meta-models has led to coining of the term meta-muddle . Individual users often exercise only a small view of a meta-muddle for tasks ranging from model creation to construction of model transformations. What is the effective meta-model that represents this view? We present a flexible meta-model pruning algorithm and tool to extract effective meta-models from a meta-muddle. We use the notion of model typing for meta-models to verify that the algorithm generates a super-type of the large meta-model representing the meta-muddle. This implies that all programs written using the effective meta-model will work for the meta-muddle hence preserving backward compatibility. All instances of the effective meta-model are also instances of the meta-muddle. We illustrate how pruning the original Uml meta-model produces different effective meta-models.

Weaving multiple aspects in sequence diagrams

Handling aspects within models looks promising for managing crosscutting concerns early in the software life-cycle, up from programming to design, analysis and even requirements. At the modeling level, even complex behavioral aspects can easily be described for instance as pairs of sequence diagrams: one for the pointcut specifying the behavior to detect, and the second one for an advice representing the wanted behavior at the join point. While this is fine for informal documentation purposes, or even intuitive enough when a single aspect has to be woven, a more precise semantics of both join point detection and advice weaving is needed for using these modeling artifacts for Model Driven Engineering activities such as code generation or test synthesis. This paper proposes various interpretations for pointcuts that allow multiple behavioral aspects to be statically woven. The idea is to allow join points to match a pointcut even when some extra-messages occur in between. However, with this new way of specifying join points, the composition of the advice with the detected part cannot any longer be just a replacement of the detected part by the advice. We have to consider the events (or the messages) of the join point, but also the events which occur between them, and merge them with the behavior specified within the advice. We thus also propose a formal definition of a new merge operator, and describe its implementation on the Kermeta platform.

Model driven design and aspect weaving

A model is a simplified representation of an aspect of the world for a specific purpose. In complex systems, many aspects are to be handled, from architectural aspects to dynamic behavior, functionalities, user-interface, and extra-functional concerns (such as security, reliability, timeliness, etc.). For software systems, the design process can then be characterized as the weaving of all these aspects into a detailed design model. Model Driven Design aims at automating this weaving process, that is automatically deriving software systems from theirs models. This paper explores the relationship between modeling and aspect weaving. It points out some of the challenges related to such automatic model weaving, illustrating them with the example of a weaving process for behavioral models represented as scenarios.