Foundations of systems and properties

Engineering of software-intensive systems is concerned with the creation and evolution of systems that shall exhibit desired properties in their execution as well as development environment. In this context, the motivation of this thesis, derived from current development practice, was twofold. Firstly, software development methods are increasingly required to extend their scope of applicability towards systems engineering. As a consequence, their modeling approaches must be able to cope with a larger diversity of systems and consequently a larger diversity of properties. But these approaches still need to provide a smooth transition to software modeling. Secondly, non-functional properties, which are largely a result of this implicit systems scope, play a major role in the way we design our software-intensive systems. The conceptual aids of current development methods, however, are still less mature in their explicit support for non-functional properties compared with their ability to support functional ones. The principal objective of this thesis is to contribute toward an improved model-based treatment of non-functional properties in development methods. Because we cannot discuss properties independently of the objects they are ascribed to, this objective amounts to a progression from modeling of software and its properties to modeling of interrelated systems and their properties. To address this aim a philosophy of properties and systems is proposed. The philosophy is expressed as a holistic conceptual model of properties and/of systems. It is complemented with some basic rules, which we call tenets. Tenets formulate how we use the philosophical knowledge. The conceptual model offers the foundations for a more generalized understanding of those fundamentally different types of systems and different types of properties that are relevant in software-intensive systems engineering. The generality of our holistic model draws the benefits from our investigations in the areas of systems science, cognitive science, and basic philosophy. The model helps to scrutinize and make sense of the large amount of data in the literature about "non-functional" issues in software engineering. The model is applicable in the derivation of methodological building blocks that can be incorporated into development methods. The building blocks include (a) a general model to discover stakeholders and properties for a given system, (b) a principled manner to trace the fundamentally different types of properties through hierarchies of systems, and (c) a proposal for the representation of systems, their properties and property traces in the UML. The concrete application of the gained knowledge to software engineering results in a proposal for a context-sensitive, customizable quality attribute model. It also results in a proposal on how to structure quality descriptions of software components. In order for such descriptions to be standardized and possibly tool-automated, this thesis proposes to utilize the Reusable Asset Specification and suggests alternatives for its XML-based representation.

Model refactoring using transformations

Slavisa Markovic

Modern software is reaching levels of complexity encountered in biological systems; sometimes comprising systems of systems each of which may include tens of millions of lines of code. Model Driven Engineering (MDE) advocates raising the level of abstraction as an instrument to deal with software complexity. It promotes usage of software models as primary artifacts in a software development process. Traditionally, these MDE models are specified by Unified Modeling Language (UML) or by a modeling language created for a specific domain. However, in the vast area of software engineering there are other techniques used to improve quality of software under development. One of such techniques is refactoring which represents introducing structured changes in software in order to improve its readability, extensibility, and maintainability, while preserving behavior of the software. The main application area for refactorings is still programming code, despite the fact that modeling languages and techniques has significantly gained in popularity, in recent years. The main topic of this thesis is making an alliance between the two virtually orthogonal techniques: software modeling and refactoring. In this thesis we have investigated how to raise the level of abstraction of programming code refactorings to the modeling level. This resulted in a catalog of model refactorings each specified as a model transformation rule. In addition, we have investigated synchronization problems between different models used to describe one software system, i.e. when one model is refactored what is the impact on all dependent models and how this impact can be formalized. We have concentrated on UML class diagrams as domain of refactorings. As models dependent on class diagrams, we have selected Object Constraint Language (OCL) annotations, and object diagrams. This thesis formalizes the most important refactoring rules for UML class diagrams and classifies them with respect to their impact on object diagrams and annotated OCL constraints. For refactoring rules that have an impact on dependent artifacts we formalize the necessary changes of these artifacts. Moreover, in this thesis, we present a simple criterion and a proof technique for the semantic preservation of refactoring rules that are defined for UML class and object diagrams, and OCL constraints. In order to be able to prove semantic preservation, we propose a model transformation approach to specify the semantics of constraint languages.

EPFL2008

On Quality Attribute Based Software Engineering

Otto Preiss, Alain Wegmann

For a software system to be perceived as a success, or even just as properly functioning, many quality attributes, besides functionality, need to be at an acceptable level. However, current software development processes focus on the functional aspects of a system to be developed. They hardly help to systematically engineer for quality attributes other than functionality. It is a system`s architecture by which such quality requirements are satisfied. In particular, software components are an incarnation of architectural means, which have come into being to better cope with the variety of quality aspects of software systems. Unfortunately, architectural artifacts appear somewhat magically sometimes, and so do components. Hence, components are not a major extension to OO in the programming language or conceptual modeling sense, but a basis to address many of the quality requirements, be they discernable or non-discernable at system runtime. CBSE, being the discipline of engineering with components, is a promising basis to more explicitly and systematically design with and for quality attributes. After defining the context and classifying quality attributes, we first illustrate the important relationship of quality attributes to use case realizations. Second, we argue for components as the fulcrum point for the realization of functional and extra-functional roles. Third, we identify ongoing research directions that we consider conducive towards a software engineering process that supports the design for functional and extra-functional requirements.

2001

Model refactoring using transformations

Slavisa Markovic

EPFL2008