Abstract

　　Software architecture is important for large systems in which it is the main means for, among other things, controlling complexity. Current ideas on software architectures were not available more than ten years ago. Software developed at that time has been deteriorating from an architectural point of view over the years, as a result of adaptations made in the software because of changing system requirements. Parts of the old software are nevertheless still being used in new product lines. To make changes in that software, like adding features, it is imperative to first adapt the software to accommodate those changes. Architecture improvement of existing software is therefore becoming more and more important.

　　This paper describes a two-phase process for software architecture improvement, which is the synthesis of two research areas: the architecture visualisation and analysis area of Philips Research, and the transformation engines and renovation factories area of the University of Amsterdam. Software architecture transformation plays an important role, and is to our knowledge a new research topic. Phase one of the process is based on Relation Partition Algebra (RPA). By lifting the information to higher levels of abstraction and calculating metrics over the system, all kinds of quality aspects can be investigated. Phase two is based on formal transformation techniques on abstract syntax trees. The software architecture improvement process allows for a fast feedback loop on results, without the need to deal with the complete software and without any interference with the normal development process.

　　Keywords: software architecture, software recovery, software rearchitecting, software architecture transformation

1 Introduction

　　Royal Philips Electronics N.V. is a world-wide company that develops low-volume professional systems (such as communication systems and medical systems) and high-volume consumer electronics systems (like digital set-top boxes and television sets). Software plays an increasingly important role in all these systems.

　　In the domain of high-volume electronics the point has been reached at which it is no longer possible to develop each new product from scratch. The software architecture of new products is of great importance with respect to satisfying the demands for increasing functionality with decreasing time-to-market. Design for reuse and open architectures are of the utmost importance with respect to software architectures for product lines [BCK98].

　　In the domain of professional systems this turning point was already reached more than ten years ago. At the time when these large software systems were developed, most of the current software architecture techniques were not available. The old software is nevertheless still used in the development of new products. Current products are more and more feature-driven, and must therefore meet high requirements with respect to the flexibility and maintainability of the software.

　　Since we want to accommodate future changes in the software in both domains, there is a need for software architecture improvement. This paper describes a new software architecture improvement process that combines two research areas.

　　The main topic of this paper is the description of a two-phase process for recovering and improving software architectures, with a clear distinction between architecture impact analysis (phase one) and software architecture transformations (phase two). Architecture impact analysis uses a model based on Relation Partition Algebra (RPA [FO94,FKO98,FO99,FK99]). Software architecture transformations use formal transformation techniques, and aim at modifying the software to meet the new architecture requirements [BKV96,BSV97,SV98,BKV98,DKV99,SV99a,SV99b,SV99c,SV99d].

　　The paper is structured as follows. In Section 2 a general description of the process for software architecture improvement is given. Section 3 describes an example to illustrate this process. In Section 4 issues related to architecture impact analysis are discussed. Section 5 focuses on the software architecture transformations and describes ideas for a set of basic transformations that are of interest for these kinds of software architecture improvements. Finally, related work is described and some conclusions are given.

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