Section: Scientific Foundations

Aspect-Oriented Programming

The main driving force for the structuring means, such as components and modules, is the quest for clean separation of concerns  [50] on the architectural and programming levels. It has, however, early been noted that concern separation in the presence of crosscutting functionalities requires specific language and implementation level support. Techniques of so-called computational reflection, for instance, Smith's 3-Lisp or Kiczales's CLOS meta-object protocol  [80] , [62] as well as metaprogramming techniques have been developed to cope with this problem but proven unwieldy to use and not amenable to formalization and property analysis due to their generality.

Aspect-Oriented Software Development  [61] , [37] has emerged over the previous decade as the domain of systematic exploration of crosscutting concerns and corresponding support throughout the software development process. The corresponding research efforts have resulted, in particular, in the recognition of crosscutting as a fundamental problem of virtually any large-scale application, and the definition and implementation of a large number of aspect-oriented models and languages.

However, most current aspect-oriented models, notably AspectJ  [60] , rely on pointcuts and advice defined in terms of individual execution events. These models are subject to serious limitations concerning the modularization of crosscutting functionalities in distributed applications, the integration of aspects with other modularization mechanisms such as components, and the provision of correctness guarantees of the resulting AO applications. They do, in particular, only permit the manipulation of distributed applications on a per-host basis, that is, without direct expression of coordination properties relating different distributed entities  [81] . Similarly, current approaches for the integration of aspects and (distributed) components do not directly express interaction properties between sets of components but rather seemingly unrelated modifications to individual components  [47] . Finally, current formalizations of such aspect models are formulated in terms of low-level semantic abstractions (see, e.g., Wand's et al semantics for AspectJ  [83] ) and provide only limited support for the analysis of fundamental aspect properties.

Recently, first approaches have been put forward to tackle these problems, in particular, in the context of so-called stateful or history-based aspect languages  [51] , [52] , which provide pointcut and advice languages that directly express rich relationships between execution events. Such languages have been proposed to directly express coordination and synchronization issues of distributed and concurrent applications  [75] , [41] , [54] , provide more concise formal semantics for aspects and enable analysis of their properties  [40] , [53] , [51] , [38] . Due to the novelty of these approaches, they represent, however, only first results and many important questions concerning these fundamental issues remain open.