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Software systems are continuously evolved to enhance or
correct functionality of earlier releases, to integrate new requirements,
or to adopt new technologies. Many of the software
systems in use today have been developed over multiple
iterations and several years by teams that changed over
time or handed over their work. As a result, such systems
have become inherently complex, difficult to understand and
costly to modify and evolve.
Common techniques for addressing complexity and for
improving comprehensibility of software systems include
modularization of concerns and structuring of the code
by applying well-established design patterns. However,
non-trivial software systems unavoidably exhibit concerns
whose implementation cannot be mapped onto a single programming
module, but cut across the system’s structure.
These crosscutting concerns lead to implementations where
multiple responsibilities are tangled inside the same module,
making it hard to distinguish them and hampering the
comprehensibility of the code and the design.
This paper shows how source code query technologies
can be used to improve comprehensibility of software systems,
and particularly of crosscutting concerns. We illustrate
general concepts of employing code queries for software
analysis and comprehension through a tool-set for
identification and documentation of crosscutting concerns
in source code.
1. Introduction
Independently of whether they work on building new
systems or, most often, on changing and extending existing
ones, software developers need to gain a quick insight
into complex software applications and into how they provide
solutions to specific problems. This task is particularly
challenging in today’s software development environments
where maintenance and evolution is carried out for
ever growing (legacy) applications and involves changing
teams, in various different locations.
A major challenge to understanding,maintaining and ensuring
the quality of software systems is the presence of
crosscutting concerns. In well-designed systems, crosscutting
implementation of concerns stems frommodularization
limitations of the employed programming paradigms which
prevent the mapping of each concern in that system to a
dedicated programming module. For example, the module
for a business object that requires secured access implements
authentication checks as a secondary concern, on top
of the core domain functionality. Similarly, typical implementations
of system-wide concerns like logging or error
handling result in multiple responsibilities, i.e. concerns,
tangled in one module, such as a class or a suproutine.
Tangling of concerns hampers program comprehension
by making it difficult to distinguish between the different
concerns implemented by one module. Furthermore, crosscutting
concerns end up scattered over multiple modules
harming the quality of the code [Eaddy, Zimmermann, Sherwood, Garg, Murphy, Nagappan, Aho, 2008].
The problem of crosscutting concerns has received significant
attention from the software research and practice
community, most recently through the popularity of aspectoriented
software development (AOSD) techniques [Filman, Elrad, Clarke, Aks¸it, editors, 2005], [Murphy, Schwanninger, 2006],
[The AspectJ Programming Guide]. The benefits of using aspect-oriented techniques for implementing
typical crosscutting concerns like logging, security
or transaction management have been discussed by
various authors [Pawlak, Retaill´e, Seinturier, 2005], [Laddad, 2003], [Colyer, Clement, Harley, Webster, editors, 2005], [Colyer, Harrop, Johnson, Vasseur, Beuche,
Beust. Point/counterpoint,2006]. However, a different line of
argument goes that AOSD techniques require expert users
and they have yet to prove their value in improving code
comprehensibility and maintainability in the long run and
for a wider range of concerns [Steimann, 2006], [Colyer, Harrop, Johnson, Vasseur, Beuche,
Beust. Point/counterpoint,2006].
In this paper we present an approach to the management
of crosscutting concerns that is a complement to AOSD
techniques, but that can also be applied independently. In
particular, we focus on the identification and comprehension
of crosscutting concerns by demonstrating a tool-set
that employs query technologies to search for and to model
typical crosscutting relations in source code.
The next section gives a background overview of such
topics as crosscutting concerns and source code queries. In
Section 3 we look at design considerations for a consistent
approach to the identification and modeling of crosscutting
concerns. Section 4 describes the tool support of
the proposed approach to concern management. We discuss
a parallel between query-based approaches and AOSD,
challenges to these approaches and interesting directions for
further investigation in Section 5, and conclude in the last
section....
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