Vol.5 No.1 March 1, 2006  
Web Technologies and Applications

Editorial  (pp001-002)
        S. Comai, M. Matera and C. Cachero   

Research articles: 
Reactivity on the Web: Paradigms and Applications of the Language XChange (pp003-024)
        F. Bry, M. Eckert, and P.-L. Patranjan
Reactivity on the Web is an emerging research issue covering: updating data on the Web, exchanging information about events (such as executed updates) between Web sites, and reacting to combinations of such events. Reactivity plays an important role for upcoming Web systems such as online marketplaces, adaptive Web and Semantic Web systems, as well as Web services and Grids. This article introduces the paradigms upon which the high-level language XChange for programming reactive behaviour and distributed applications on the Web relies. Then, it briefly presents the main syntactical constructs of XChange and their declarative and operational semantics.

Supporting Web Applications development with a PLA (pp025-042)
        L. Balzerani, G. De Angelis, D. Di Ruscio, and A. Pierantonio 
Web applications have become crucial elements of the global information infrastructure, evolving from simple collections of static pages to distributed applications. Since Web applications often share similar behaviors, shifting the focus from the design of single applications to that of system families is an effective way to pursue synergy effects in software development. The paper illustrates Koriandol, a product line architecture designed to develop, deploy and maintain families of Web applications. Specific family members are assembled from reusable components which support variability determination through built--in reflective mechanisms. These provide the ability to bind variation points to specific variants even post deployment, making applications widely reconfigurable.

Extending Web Engineering Models and Tools for Automatic Usability Validation (pp043-064)
        R. Atterer, A. Schmidt, and H. Hußmann  
In this paper, we present ideas of how to improve the quality of automated web usability validators. This can be achieved by taking advantage of the models of established Web Engineering solutions. We begin by analysing two of the currently available Web Engineering solutions (UWE and OO-H) with regard to the question whether any websites created with them have a high usability. Additionally, it is examined whether the respective models can express usability aspects. In a small case study, an example website is created by converting a model to an implementation manually. Special attention is paid to usability issues regarding both the generated pages and the development process. Subsequently, we take a look at existing implementations of usability validators, noting how the quality of their results is often not optimal. This is due to the fact that not enough abstract information is available. In the next step, we identify existing Web Engineering model properties which can be used to improve the checks, and propose further extensions to models.

Contracts for Cooperation between Web Service Programmers and HTML Designers (pp065-090)
        H. Bottger, A. Møller, and M. Schwartzbach
Interactive Web services consist of a mixture of HTML fragments and program code. The fragments, which are maintained by designers, are combined to form HTML pages that are shown to the clients. The code, which is maintained by programmers, is executed on the server to handle the business logic. Current Web service frameworks provide little help in separating these constituents, which complicates cooperation between programmers and HTML designers. We propose a system based on XML templates and formalized contracts allowing a flexible separation of concerns. The contracts act as interfaces between the programmers and the HTML designers and permit tool support for statically checking that both parties fulfill their obligations. This ensures that (1) programmers and HTML designers work more independently focusing on their own expertise, (2) the Web service implementation is better structured and thus easier to develop and maintain, (3) it is guaranteed that only valid HTML is sent to the clients even though it is constructed dynamically, (4) the programmer uses the XML templates consistently, and (5) the form input fields being sent to the client always match the code receiving those values. Additionally, we describe tools that aid in the construction and management of contracts and XML templates.

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