Database replication based on group communication systems has recently been proposed as an efficient and resilient solution for large-scale data management. However, its evaluation has been conducted either on simplistic simulation models, which fail to assess concrete implementations, or on complete system implementations which are costly to test with realistic large-scale scenarios. This paper presents a tool that combines implementations of replication and communication protocols under study with simulated network, database engine, and traffic generator models. Replication components can therefore be subjected to realistic large scale loads in a variety of scenarios, including fault-injection, while at the same time providing global observation and control. The paper shows first how the model is configured and validated to closely reproduce the behavior of a real system, and then how it is applied, allowing us to derive interesting conclusions both on replication and communication protocols and on their implementations.

We have experimented with modeling some of the key concepts of the VDM specification language inside the functional programming language Haskell. For instance, VDM’s sets and maps are directly available as data types defined in standard libraries; we merely needed to define some additional functions to make the match complete. A bigger challenge is posed by VDM’s data type invariants, and pre- and post- conditions. For these we resorted to Haskell’s constructor class mechanism, and its support for monads. This allows us to switch between different modes of evaluation (e.g. with or without property checking) by simply coercing user defined functions and operations to different specific types.

Program slicing is a well known family of techniques used to identify code fragments which depend on or are depended upon specific program entities. They are particularly useful in the areas of reverse engineering, program understanding, testing and software maintenance. Most slicing methods, usually targeting either the imperative or the object oriented paradigms, are based on some sort of graph structure representing program dependencies. Slicing techniques amount, therefore, to (sophisticated) graph transversal algorithms. This paper proposes a completely different approach to the slicing problem for functional programs. Instead of extracting program information to build an underlying dependencies’ structure, we resort to standard program calculation strategies, based on the so-called Bird-Meertens formalism. The slicing criterion is specified either as a projection or a hiding function which, once composed with the original program, leads to the identification of the intended slice. Going through a number of examples, the paper suggests this approach may be an interesting, even if not completely general alternative to slicing functional programs.

The theories and practices of software engineering and of human-computer interaction have, to a great extent, evolved separately. It seems obvious that the development of an interactive system would benefit from input from both disciplines. In practice, however, the communication between the two communities has been difficult. Models can be a particularly good tool for communication. For that to happen the differences between the models used by each community must first be identified and understood. This paper looks at the gaps between the models used by the software engineering and the human-computer interaction communities. It identifies where differences between these models can be found, and some aspects that need addressing in order to promote better communication.

Internet accessibility for the visually impaired community is still an open issue. Guidelines have been issued by the W3C consortium to help web designers to improve web site accessibility. However several studies show that a significant percentage of web page creators are still ignoring the proposed guidelines. Several tools are now available, general purpose, or web specific, to help visually impaired readers. But is reading a web page enough? Regular sighted users are able to scan a web page for a particular piece of information at high speeds. Shouldn't visually impaired readers have the same chance? This paper discusses some features already implemented to improve accessibility and presents a user feedback report regarding the AudioBrowser, a talking browser. Based on the user feedback the paper also suggests some avenues for future work in order to make talking browsers and screen readers compatible.

Esta comunicação é uma tentativa de sistematizar a aplicação de um método de análise de usabilidade: o cognitive walkthrough. Pode então ser utilizada como um tutorial, apresentando um exemplo da aplicação do método a uma situação prática.