26464031
A Taxonomy of Web Services Using CSP
Terms such as conversational and stateless are widely used in the taxonomy of web services. We give formal definitions of these terms using the CSP process algebra. Within this framework we also define the notion of Service-Oriented Architecture. These definitions are then used to prove important scalability properties of stateless services. The use of formalism should allow recent debates, concerning how and whether web services provide standardized access to state, to progress more rigorously.
29669559
Relating Z and First-Order Logic
Despite being widely regarded as a gloss on first-order logic and set theory, Z has not been found to be very supportive of proof. This paper attempts to distinguish between the different philosophies of proof in Z. It discusses some of the issues which must be addressed in creating a proof technology for Z, namely schemas, undefinedness, and what kind of logic to use.
37164715
The Cogito Development System
The Cogito system provides comprehensive support for the development of specifications written in the Sum language (a modular extension of Z). The tool-set provides technology to aid in the construction, analysis and development of Sum specifications. Ada code is the final result of a development in Cogito.
14876854
Security principles for public-resource modeling research
Large-scale distributed computing projects have many security concerns due to their public and often "open" nature. Climateprediction.net (CPDN) is taking the concept of public-resource, high-throughput grid computing a stage further, by using it for a major piece of modeling research. The aim is to harness the spare CPU cycles of potentially millions of individual users' PCs to run a massive ensemble of climate simulations. In doing so it has been faced with a range of security and integrity issues beyond those encountered by previous projects but likely also to confront similar initiatives in the future. This paper introduces the project and its software architecture, and outlines a threat model for such situations, including threats to participants, threats to the experiment and threats to other stakeholders. It goes on to discuss how these threats have been addressed, with the procedures presented expected to form a valuable foundation for an increasing number of similar projects.
26964761
Relating Z and First-Order Logic
Abstract. Despite being widely regarded as a gloss on first-order logic and set theory, Z has not been found to be very supportive of proof. This paper attempts to distinguish between the different philosophies of proof in Z. It discusses some of the issues which must be addressed in creating a proof technology for Z, namely schemas, undefinedness, and what kind of logic to use.
23372292
A Calculus for Schemas in Z
The popularity and flexibility of the Z notation can largely be attributed to its notion of schemas. We describe these schemas and illustrate their various common uses in Z. We also present a collection of logical laws for manipulating these schemas. These laws are capable of supporting reasoning about the Z schema calculus in its full generality. This is demonstrated by presenting some theorems about the removability of schemas from Z specifications, together with outline proofs. We survey briefly models against which this logical system may be proven sound, and other related logics for Z.
5379517
Packing Steiner Trees: Further Facets
Abstract In this paper we continue the investigations in [3] for the Steiner tree packing polyhedron. We present several new classes of valid inequalities and give sufficient (and necessary) conditions for these inequalities to be facet-definining. It is intended to incorporate these inequalities into an existing cutting plane algorithm that is applicable to practical problems arising in the design of electronic curcuits.
34039430
A model of information systems development project performance
. Performance in information systems development (ISD) projects can be critical to business success. But, while project performance has been the subject of much debate, there has been little empirical research into its determinants. A survey of IS projects in the UK and New Zealand is analysed to test hypotheses concerning performance in terms of both project completion and budget (time-cost) variances. Subsequently, a secondary analysis of the findings is used to build a more complete empirical model of project performance. The paper helps to develop the theory of IS development project performance and also has significant implications for practice. Discussion of the findings highlights the importance of project team dynamics, risk management, senior management support for strategic projects and user participation in ensuring successful IS project performance.
10076896
Agent Assistance for 3D World Navigation
This paper presents mechanisms and approaches to assist user navigation and exploration within 3-dimensional worlds. Specifically, we advocate the deployment of an agent based approach for dynamic system assistance and intervention. An algorithm has been developed, that produces a performance measure, which is employed by the intelligent agent to activate system interventions. We outline the importance of providing discrete navigational cues to users in order to increase their sense of immersion and their overall satisfaction while working within the 3D world. We present HADES - the Home of the Adaptive Environmental System, which is a 3-dimensional world within which the intelligent agent is immersed. The agent therefore has the ability to transform this 3D world into an intelligent environment. HADES reacts proactively to users' movements and offers navigational help indirectly. Indirect navigational support increases the user's satisfaction with his own performance and therefore endorses the user's sense of immersion.
145836
Packing Steiner trees: polyhedral investigations
LetG=(V, E) be a graph andT⊆V be a node set. We call an edge setS a Steiner tree forT ifS connects all pairs of nodes inT. In this paper we address the following problem, which we call the weighted Steiner tree packing problem. Given a graphG=(V, E) with edge weightswe, edge capacitiesce,e∈E, and node setT1,…,TN, find edge setsS1,…,SN such that eachSk is a Steiner tree forTk, at mostce of these edge sets use edgee for eache∈E, and the sum of the weights of the edge sets is minimal. Our motivation for studying this problem arises from a routing problem in VLSI-design, where given sets of points have to be connected by wires. We consider the Steiner tree packing problem from a polyhedral point of view and define an associated polyhedron, called the Steiner tree packing polyhedron. The goal of this paper is to (partially) describe this polyhedron by means of inequalities. It turns out that, under mild assumptions, each inequality that defines a facet for the (single) Steiner tree polyhedron can be lifted to a facet-defining inequality for the Steiner tree packing polyhedron. The main emphasis of this paper lies on the presentation of so-called joint inequalities that are valid and facet-defining for this polyhedron. Inequalities of this kind involve at least two Steiner trees. The classes of inequalities we have found form the basis of a branch & cut algorithm. This algorithm is described in our companion paper (in this issue).
16348358
Agent Chameleons: Virtual Agents Real Intelligence
Agent Chameleons provides virtual agents powered by real intelligence, delivering next generation autonomic entities that can seamlessly migrate, mutate and evolve on their journey between and within physical and digital information spaces.