Tom Mens

A survey of software refactoring

We provide an extensive overview of existing research in the field of software refactoring. This research is compared and discussed based on a number of different criteria: the refactoring activities that are supported, the specific techniques and formalisms that are used for supporting these activities, the types of software artifacts that are being refactored, the important issues that need to be taken into account when building refactoring tool support, and the effect of refactoring on the software process. A running example is used to explain and illustrate the main concepts.

A state-of-the-art survey on software merging

Software merging is an essential aspect of the maintenance and evolution of large-scale software systems. This paper provides a comprehensive survey and analysis of available merge approaches. Over the years, a wide variety of different merge techniques has been proposed. While initial techniques were purely based on textual merging, more powerful approaches also take the syntax and semantics of the software into account. There is a tendency towards operation-based merging because of its increased expressiveness. Another tendency is to try to define merge techniques that are as general, accurate, scalable, and customizable as possible, so that they can be used in any phase in the software life-cycle and detect as many conflicts as possible. After comparing the possible merge techniques, we suggest a number of important open problems and future research directions.

Challenges in software evolution

Todays information technology society increasingly relies on software at all levels. Nevertheless, software quality generally continues to fall short of expectations, and software systems continue to suffer from symptoms of aging as they are adapted to changing requirements and environments. The only way to overcome or avoid the negative effects of software aging is by placing change and evolution in the center of the software development process. In this article we describe what we believe to be some of the most important research challenges in software evolution. The goal of this document is to provide novel research directions in the software evolution domain.

Using Description Logic to Maintain Consistency between UML Models

A software design is often modelled as a collection of UML diagrams. There is an inherent need to preserve consistency between these diagrams. Moreover, through evolution those diagrams get modified leading to possible inconsistency between different versions of the diagrams. State-of-the-art UML CASE tools provide poor support for consistency maintenance. To solve this problem, an extension of the UML metamodel enabling support for consistency maintenance and a classification of inconsistency problems is proposed. To achieve the detection and resolution of consistency conflicts, the use of description logic (DL) is presented. DL has the important property of being a decidable fragment of first-order predicate logic. By means of a number of concrete experiments in Loom, we show the feasibility of using this formalism for the purpose of maintaining consistency between (evolving) UML models.

Identifying refactoring opportunities using logic meta programming

We show how automated support can be provided for identifying refactoring opportunities, e.g., when an applications design should be refactored and which refactoring(s) in particular should be applied. Such support is achieved by using the technique of logic meta programming to detect so-called bad smells and by defining a framework that uses this information to propose adequate refactorings. We report on some initial but promising experiments that were applied using the proposed techniques.

Detecting model inconsistency through operation-based model construction

Nowadays, large-scale industrial software systems may involve hundreds of developers working on hundreds of different but related models representing parts of the same system specification. Detecting and resolving structural inconsistencies between these models is then critical. In this article we propose to represent models by sequences of elementary construction operations, rather than by the set of model elements they contain. Structural and methodological consistency rules can then be expressed uniformly as logical constraints on such sequences. Our approach is meta-model independent, allowing us to deal with consistency between different models whatever their kind. We have validated our approach by building a Prolog engine that detects violations of structural and methodological constraints specified on UML 2.1 models and requirement models. This engine has been integrated into two contemporary UML-based modelling environments, Eclipse EMF and rational software architect (RSA).

Analysing refactoring dependencies using graph transformation

Refactoring is a widely accepted technique to improve the structure of object-oriented software. Nevertheless, existing tool support remains restricted to automatically applying refactoring transformations. Deciding what to refactor and which refactoring to apply still remains a difficult manual process, due to the many dependencies and interrelationships between relevant refactorings. In this paper, we represent refactorings as graph transformations, and we propose the technique of critical pair analysis to detect the implicit dependencies between refactorings. The results of this analysis can help the developer to make an informed decision of which refactoring is most suitable in a given context and why. We report on several experiments we carried out in the AGG graph transformation tool to support our claims.

Formalising Behaviour Preserving Program Transformations

The notion of refactoring --transforming the source-code of an object-oriented program without changing its external behaviour-- has increased the need for a precise definition of refactorings and their properties. This paper introduces a graph representation of those aspects of the source code that should be preserved by a refactoring, and graph rewriting rules as a formal specification for the refactoring transformations themselves. To this aim, we use type graphs, forbidden subgraphs, embedding mechansims, negative application conditions and controlled graph rewriting. We show that it is feasible to reason about the effect of refactorings on object-oriented programs independently of the programming language being used. This is crucial for the next generation of refactoring tools.

Detecting and resolving model inconsistencies using transformation dependency analysis

Model inconsistency management is a crucial aspect of model-driven software engineering. It is therefore important to provide automated support for this activity. The problem is, however, that the resolution of inconsistencies may give rise to new inconsistencies. To address this problem, we propose to express inconsistency detection and resolutions as graph transformation rules, and to apply the theory of critical pair analysis to analyse potential dependencies between the detection and resolution of model inconsistencies. As a proof-of-concept, we report on an experiment that we have carried out along these lines using the critical pair analysis algorithm implemented in the state-of-the-art graph transformation tool AGG. The results show that both anticipated and unexpected dependencies between inconsistency detection and resolution rules are found by AGG. We discuss how the integration of the proposed approach into contemporary modelling tools may improve inconsistency management in various ways.

Towards automating source-consistent UML refactorings

With the increased interest in refactoring, UML tool vendors seek ways to support software developers in applying a (sequence of) refactoring(s). The problem with such tools is that the UML metamodel – on which their repository is based – is inadequate to maintain the consistency between the model and the code while one of them gets refactored. Therefore, we propose a set of minimal extensions to the UML metamodel, which is sufficient to reason about refactoring for all common OO languages. For instance, by specifying pre- and postconditions in OCL, we are able to compose primitive refactorings, verify preservation of program behavior, and trigger refactorings based on code smells. This way, we provide future MDA tools with the ability to improve existing UML designs, yet keeping them in synch with the underlying code base.