Jilles van Gurp

A taxonomy of variability realization techniques

Development of software product families relies heavily on the use of variability to manage the differences between products by delaying design decisions to later stages of the development and usage of the constructed software systems. Implementation of variability is not a trivial task, and is governed by a number of factors. In this paper, we describe the factors that are relevant in determining how to implement variability, and present a taxonomy of variability realization techniques. Copyright

Design erosion: problems and causes

Design erosion is a common problem in software engineering. We have found that invariably, no matter how ambitious the intentions of the designers were, software designs tend to erode over time to the point that redesigning from scratch becomes a viable alternative compared to prolonging the life of the existing design. In this paper, we illustrate how design erosion works by presenting the evolution of the design of a small software system. In our analysis of this example, we show how design decisions accumulate and become invalid because of new requirements. Also it is argued that even an optimal strategy for designing the system (i.e. no compromises with respect to e.g. cost are made) does not lead to an optimal design because of unforeseen requirement changes that invalidate design decisions that were once optimal.

A framework for capturing the relationship between usability and software architecture

Usability is increasingly recognized as an essential factor that determines the success of software systems. Practice shows that for current software systems, most usability issues are detected during testing and deployment. Fixing usability issues during this late stage of the development proves to be very costly. Some usability-improving modifications such as usability patterns may have architectural implications. We believe that the software architecture may restrict usability. The high costs associated with fixing usability issues during late-stage development prevent developers from making the necessary adjustments for meeting all the usability requirements. To improve upon this situation, we have investigated the relationship between usability and software architecture to gain a better understanding of how the architecture restricts the level of usability. Our article makes a number of contributions; a framework is presented that expresses the relationship between usability and software architecture. The framework consists of an integrated set of design solutions such as usability patterns and usability properties that have been identified in various cases in industry, modern day software and literature surveys. These solutions, in most cases, have a positive effect on usability but are difficult to retrofit into applications because they have architectural impact. Our framework may be used to guide and inform the architectural design phase. This may decrease development costs by reducing the amount of usability issues that need to be fixed during the later stages of development. Copyright

Design preservation over subsequent releases of a software product: a case study of Baan ERP

SUMMARY We present the results of two case studies we conducted at Baan in the Netherlands. At the time of conducting the case studies, Baan was part of Invensys plc. (Baan is now owned by SSA Global Technologies.) In these case studies we investigated how companies identify design erosion and address this in their software, a practice we call ‘design preservation’. In this study, we selected two sub-systems in Baan products that had recently been subjected to extensive maintenance activities because they were eroded. In this paper, we analyze the problems these systems had, how Baan identified that these systems were problematic, and the remedies that were used to address the problems. In addition to confirming some of our earlier conclusions, we have been able to extract some common causes for design erosion problems as well as a number of recommended design preservation practices, which, at least for Baan, have proven to be very effective in strengthening design preservation. Copyright c � 2005 John Wiley & Sons, Ltd.

Software architecture analysis of usability

Studies of software engineering projects show that a large number of usability related change requests are made after its deployment. Fixing usability problems during the later stages of development often proves to be costly, since many of the necessary changes require changes to the system that cannot be easily accommodated by its software architecture. These high costs prevent developers from meeting all the usability requirements, resulting in systems with less than optimal usability. The successful development of a usable software system therefore must include creating a software architecture that supports the right level of usability. Unfortunately, no documented evidence exists of architecture level assessment techniques focusing on usability. To support software architects in creating a software architecture that supports usability, we present a scenario based assessment technique that has been successfully applied in several cases. Explicit evaluation of usability during architectural design may reduce the risk of building a system that fails to meet its usability requirements and may prevent high costs incurring adaptive maintenance activities once the system has been implemented.

Approach for Dynamically Composing Decentralised Service Architectures with Cross-Cutting Constraints

The emergence of open, composable Internet services and mashups means that services cannot be composed in a centralised manner. Despite this, cross-cutting constraints might exist between services, stemming from, e.g., security. Especially when used with mobile devices, these service compositions need to be constructed at runtime. This paper proposes a knowledge-based approach for dynamically finding and validating decentralised service compositions while taking into account cross-cutting constraints. The approach is exemplified with a case of a shopping mall portal.

Mobile service oriented architectures (MOSOA)

Mobile services hold a promise of utilizing the phone also for other purposes than purely communication. However, repeated attempts at realizing mobile services in the market place have been met with limited success. This article (1) defines the architectural drivers that drive success or failure of mobile services, (2) analyzes three different architectural styles of realizing such a mobile service using the example of a movie ticket selling service and (3) presents the results of this analysis. The main result of the analysis is that a serious conflict exists between usability and essentially all the other architectural drivers included in our analysis, i.e. portability, deployability and scalability. This is due to the fact that, because of the restricted state of the art technology, only native client applications offer satisfactory usability, but these do not satisfy the other drivers.