Recent years have seen a shift in perception of the nature of HCI and interactive systems. As interface work has increasingly become a focus of attention for the social sciences, we have expanded our appreciation of the importance of issues such as work practice, adaptation, and evolution in interactive systems. The reorientation in our view of interactive systems has been accompanied by a call for a new model of design centered around user needs and participation. This article argues that a new process of design is not enough and that the new view necessitates a similar reorientation in the structure of the systems we build. It outlines some requirements for systems that support a deeper conception of interaction and argues that the traditional system design techniques are not suited to creating such systems. Finally, using examples from ongoing work in the design of an open toolkit for collaborative applications, it illustrates how the principles of computational reflection and metaobject protocols can lead us toward a new model based on open abstraction that holds great promise in addressing these issues.

Reflection has emerged as an important technique in the field of programming language design. Some research has also been carried out in the field of operating systems. In contrast, however, there has been little research in the area of reflective distributed systems. This paper presents an analysis of existing work on reflection and argues that reflection can have an important role to play in distributed systems, in general, and middleware platforms, in particular. The paper concludes with some thoughts on the design of reflective middleware platforms.

The design of Computer-Supported Cooperative Work (CSCW) systems involves a variety of disciplinary approaches, drawing as much on sociological and psychological perspectives on group and individual activity as on technical approaches to designing distributed systems. Traditionally, these have been applied independently---the technical approaches focussing on design criteria and implementation strategies, the social approaches focussing on the analysis of working activity with or without technological support. However, the disciplines are more strongly related than this suggests. Technical strategies---such as the mechanisms for data replication, distribution and coordination---have a significant impact on the forms of interaction in which users can engage, and therefore on how their work proceeds. Consequently, the findings of sociological and psychological investigations of collaborative working have direct impact for how we go about designing collaborative systems. I...

The past few years have seen a steadily increasing understanding of the need for customisation and tailorability in a range of computational systems. This has resulted both from a greater understanding of the role of individual and organisational work practices in human-computer interaction, and from the application of systems to more complex domains of activity. The increasing requirement that systems provide flexible and customisable behaviour, and that this customisation reach deeper into the system, forces a reconsideration of the techniques by which customisable systems are constructed.

this paper is to investigate the usefulness of generic type schemes for type inference in polymorphic programming languages. In particular, we are not interested in types of variables, but in types of variable references [11]. A variable may have different types in different program branches, e.g. in the term if (nump x) x x, variable x is numerical in the then-branch, but guaranteed to be non-numerical in the else-branch. Thus, there is a need for an adequate type representation for predicate functions like nump.

This DEA internship report proposes a study and a classification of best known Metaobject Protocols (MOPs). Far from being totally exhaustive, it explains the nowadays motivation and use of MOPs by practical examples in many application areas. These examples naturally lead to distinguish different kinds of use of MOPs techniques and also, as one can expect, different kinds of implementation. These functional and implementational differences allow us to classify MOPs in two large families: behavioral and structural oriented MOPs. The former is mainly used to deal with behavioral issues and is mostly used in system approaches. The later is more used in approaches consisting in controlling languages and structural features. This classification naturally leads to the idea that, to efficiently build effective object-oriented distributed applications, we should be able to consistently use those two approaches within the same development process, and even within the same system. This is the ...

We report the application of an OO design methodology to the reconstruction of an old program, namely the OPS5 production rule system. It exhibits the worst excesses of imperative coding, but is one of the most widely used and understood expert system shells. We started from OPS5 because of the many publicly available rule-sets which could be used for testing, aiming to reconstruct it as a concurrent object-oriented program. A signicant corollary of the use of objects for the discrimination network is that productions may be added incrementally, whereas the Rete network requires recompilation of the rule set.

this paper, I illustrate this by considering cases in which patients produce unsolicited turns at talk 1 while a prescription is being issued, either to raise issues concerning the prescription per se or to introduce unrelated topics (concerning, for example, other complaints, social issues, or problems encountered by members of their family). Subsequently, I discuss some of the potential design implications of the findings and suggest that the linkage between human-computer interaction and face-to-face interpersonal communication raises important issues for the field of HCI