My thesis is that practical language support can be provided for Service-Level Agreements (SLAs) for Application-Service Provision (ASP), which is better than that provided by pre-existing languages in that: it provides greater assistance in expressing conditions that mitigate the risks inherent in ASP; and disputes related to agreements expressed in this manner may be more easily resolved in so as to respect the original intent of the parties. I support this thesis by establishing requirements for SLAs for ASP based on an account of a typical ASP infrastructure and business model. These identify the particular risks inherent in ASP, permit comparisons between ASP SLA languages, and guide the development of an abstract, extensible, domain-specific language, SLAng. SLAng is defined using a meta-modelling approach that allows a high degree of precision in the specification of its semantics, traceability from SLA to language specification, and the testing of the language and SLAs to ensure they capture the original intent of the parties. SLAng supports the expression of mutually-monitorable SLAs, for which the determination of compliance depends only on events visible to both client and provider of the service. I demonstrate that such SLAs are the most monitorable possible in a typical ASP scenario, given current monitoring technology, and describe an approximately-monitorable constraint on the accuracy of evidence used to administer such SLAs. SLAng is shown to be of practical use in a case study, evaluated against the original requirements, and compared with pre-existing languages. The evaluation of SLAng is enhanced using metrics developed to assist in assessing the contribution of a domain-specific language specification to encoding the meaning of statements in that language.

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Many businesses produce documents as part of their daily activities: software engineers produce requirements specifications, design models, source code, build scripts and more; business analysts produce glossaries, use cases, organisation charts, and domain ontology models; service providers and retailers produce catalogues, customer data, purchase orders, invoices and web pages. What these examples have in common is that the content of documents is often semantically related: source code should be consistent with the design model, a domain ontology may refer to employees in an organisation chart, and invoices to customers should be consistent with stored customer data and purchase orders. As businesses grow and documents are added, it becomes difficult to manually track and check the increasingly complex relationships between documents. The problem is compounded by current trends towards distributed working, either over the Internet or over a global corporate network in large organisations. This adds complexity as related information is not only scattered over a number of documents, but the documents themselves are distributed across multiple physical locations. This thesis addresses the problem of managing the consistency of distributed and possibly heterogeneous documents. “Documents” is used here as an abstract term, and does not necessarily refer to a human readable textual representation. We use the word to stand for a file or data source holding structured information, like a database table, or some source of semi-structured information, like a file of comma-separated values or a document represented in a hypertext markup language like XML [Bray et al., 2000]. Document heterogeneity comes into play when data with similar semantics is represented in different ways: for example, a design model may store a class as a rectangle in a diagram whereas a source code file will embed it as a textual string; and an invoice may contain an invoice identifier that is composed of a customer name and date, both of which may be recorded and managed separately. Consistency management in this setting encompasses a number of steps. Firstly, checks must be executed in order to determine the consistency status of documents. Documents are inconsistent if their internal elements hold values that do not meet the properties expected in the application domain or if there are conflicts between the values of elements in multiple documents. The results of a consistency check have to be accumulated and reported back to the user. And finally, the user may choose to change the documents to bring them into a consistent state. The current generation of tools and techniques is not always sufficiently equipped to deal with this problem. Consistency checking is mostly tightly integrated or hardcoded into tools, leading to problems with extensibility with respect to new types of documents. Many tools do not support checks of distributed data, insisting instead on accumulating everything in a centralized repository. This may not always be possible, due to organisational or time constraints, and can represent excessive overhead if the only purpose of integration is to improve data consistency rather than deriving any additional benefit. This thesis investigates the theoretical background and practical support necessary to support consistency management of distributed documents. It makes a number of contributions to the state of the art, and the overall approach is validated in significant case studies that provide evidence of its practicality and usefulness.

Mobile computing devices, such as personal digital assistants and mobile phones, are becoming increasingly popular, smaller, more capable and even fashionable personal items. Combined with the recent advent of wireless networking techniques, users are equipped with mobile devices of significant computational abilities, which are able to wirelessly access information by dynamically connecting to many different networks. Despite the ubiquity of mobile devices, mobile systems are built using monolithic architectures, use a small set of predefined interaction paradigms and do not exploit or adapt to the dynamicity of their local or remote context. Applications deployed on mobile devices face considerable challenges posed by their changing surroundings. One of the main peculiarities of mobile devices is heterogeneity, which may occur in software, hardware and network protocols. Mobile systems may carry a large number of different applications, use different operating systems and middleware and, often, have more than one network interface. A further challenge is their considerable variation in the computational resources available, such as battery power, CPU speed, network bandwidth and volatile and persistent memory. Moreover, mobile computing systems are highly dynamic systems, in terms of their surroundings, implying that the requirements for applications deployed on a mobile device are a moving target. Changes in the requirements (such as integration with a new service) may require changes to the application. Consequently, these changes may mean that the application behaviour needs to adapt. This thesis argues that the potential of the ubiquity of mobile devices cannot be realised using static and monolithic architectures, as mobile systems need to be able to adapt to accommodate changes to their environment. It investigates the use of three technologies to offer adaptation to mobile devices: Logical mobility techniques, component systems and middleware technologies. More specifically, this thesis presents the SATIN (System Adaptation Targeting Integrated Networks) component metamodel, a lightweight local component metamodel that offers the flexible use of logical mobility primitives. The metamodel is instantiated to build the SATIN middleware system, a component-based mobile computing middleware that uses the mobility primitives exported by the metamodel to reconfigure itself and applications running on top of it. The suitability of SATIN for the creation of adaptable mobile systems is demonstrated, by using it to implement and evaluate a number of applications showing different aspects of adaptation. Moreover, existing projects are reengineered to run as SATIN components, showing the flexibility of the approach and the advantages gained over the originals.

The increasing popularity of mobile devices, such as mobile phones and personal digital assistants, and advances in wireless networking technologies, are enabling new classes of applications that present challenging problems to application designers. Applications have to be aware of, and adapt to, variations in the execution context, such as fluctuating network bandwidth and decreasing battery power, in order to deliver a good quality of service to their users. We argue that building applications directly on top of the network operating system would be extremely tedious and error-prone, as application developers would have to deal with these issues explicitly, and would consequently be distracted from the actual requirements of the application they are building. Rather, a middleware layered between the network operating system and the application should provide application developers with abstractions and mechanisms to deal with them. We investigate the principle of reflection and demonstrate how it can be used to support context-awareness and dynamic adaptation to context changes. We offer application engineers an abstraction of middleware as a dynamically customisable service provider, where each service can be delivered using different policies when requested in different contexts. Based on this abstraction, current middleware behaviour, with respect to a particular application, is reified in an application profile, and made accessible to the application for run-time inspection and adaptation. Applications can use the meta-interface that the middleware provides to change the information encoded in their profile, thus tailoring middleware behaviour to the user's needs. However, while doing so, conflicts may arise; different users may have different quality-of-service needs, and applications, in an attempt to full these needs, may customise middleware behaviour in conflicting ways. These conflicts have to be resolved in order to allow applications to come to an agreement, and thus be able to engage successful collaborations. We demonstrate how microeconomic techniques can be used to treat these kinds of conflicts. We offer an abstraction of the mobile setting as an economy, where applications compete to have a service delivered according to their quality-of-service needs. We have designed a mechanism where middleware plays the role of the auctioneer, collecting bids from the applications and delivering the service using the policy that maximises social welfare; that is, the one that delivers, on average, the best quality-of-service. We formalise the principles discussed above, namely reflection to support context-awareness and microeconomic techniques to support conflict resolution. To demonstrate their effectiveness in fostering the development of context-aware applications, we discuss a middleware architecture and implementation (CARISMA) that embed these principles, and report on performance and usability results obtained during a thorough evaluation stage.

A multi-agent system (MAS) is usually understood as a system composed of interacting autonomous agents. In this sense, MAS have been employed successfully as a modelling paradigm in a number of scenarios, especially in Computer Science. However, the process of modelling complex and heterogeneous systems is intrinsically prone to errors: for this reason, computer scientists are typically concerned with the issue of verifying that a system actually behaves as it is supposed to, especially when a system is complex. Techniques have been developed to perform this task: testing is the most common technique, but in many circumstances a formal proof of correctness is needed. Techniques for formal verification include theorem proving and model checking. Model checking techniques, in particular, have been successfully employed in the formal verification of distributed systems, including hardware components, communication protocols, security protocols. In contrast to traditional distributed systems, formal verification techniques for MAS are still in their infancy, due to the more complex nature of agents, their autonomy, and the richer language used in the specification of properties. This thesis aims at making a contribution in the formal verification of properties of MAS via model checking. In particular, the following points are addressed: • Theoretical results about model checking methodologies for MAS, obtained by extending traditional methodologies based on Ordered Binary Decision Diagrams (OBDDS) for temporal logics to multi-modal logics for time, knowledge, correct behaviour, and strategies of agents. Complexity results for model checking these logics (and their symbolic representations). • Development of a software tool (MCMAS) that permits the specification and verification of MAS described in the formalism of interpreted systems. • Examples of application of MCMAS to various MAS scenarios (communication, anonymity, games, hardware diagnosability), including experimental results, and comparison with other tools available.

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No description available.

Parameter-Driven Systems (PDS) are widely used in commerce for large-scale applications. Reusability is achieved with a PDS design by relocating implicit control structures in the software and the storage of explicit data in database files. This approach can accommodate various user requirements without tedious modification of the software. In order to specify appropriate parameters in a system, knowledge of both business activities and system behaviour are required. For large, complex software packages, this task becomes time consuming and requires specialist knowledge, yet the consistency and correctness still cannot be guaranteed. My research studied the types of knowledge required and agents involved in the PDS customisation. The work also identified the associated problems and constraints. A solution is proposed and implemented as an Intelligent Assistant prototype than a manual approach. Three areas of achievement have been highlighted: 1. The characteristics and problems of maintaining parameter instances in a PDS are defined. It is found that the verification is not complete with the technical/structural knowledge alone, but a context is necessary to provide semantic information and related business activities (thus the implemented parameters) so that mainline functions can relate with each other. 2. A knowledge-based modelling approach has been proposed and demonstrated via a practical implementation. A Specification Language was designed which can model various types of knowledge in a PDS and encapsulate relationships. The Knowledge-Based System (KBS) developed verifies parameters based on the interpreted model of a given context. 3. The performance of the Intelligent Assistant prototype was well received by the domain specialist from the participating organisation. The modelling and KBS approach developed in my research offers considerable promise in solving practical problems in the software industry.

Please read the abstract (Summary) in the section 00front of this document / Dissertation (MSc (Mathematics Education))--University of Pretoria, 2007. / Mathematics and Applied Mathematics / unrestricted