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In this thesis, we study the problem of evaluating set expressions over sorted sets in the comparison model. The problem arises in the context of evaluating search queries in text database systems; most text search engines maintain an inverted list, which consists of a set of documents that contain each possible word. Thus, answering a query is reduced to computing the union, the intersection, or a more complex set expression over sets of documents containing the words in the query. At the first step, for a given expression on a number of sets and the sizes of the sets, we investigate the worst-case complexity of evaluating the expression in terms of the sizes of the sets. We prove lower bounds and provide algorithms with the matching running time up to a constant factor. We then refine the problem further and design an algorithm that computes such expressions according to the degree by which the input sets are interleaved rather than only considering sets sizes. %We prove the running time of our algorithm is asymptotically optimal. We prove the optimality of our algorithm by way of presenting a matching lower bound sensitive to the interleaving measure. The algorithms we present are different in the set of set operators they allow in input expressions. We provide algorithms that are worst-case optimal for inputs with union, intersection, and symmetric difference operators. One of the algorithms we provide also supports minus and complement operators and is conjectured to be optimal when an input is allowed to contain these operators as well. We also provide a worst-case optimal algorithm for the form of problem where the input may contain "threshold'" operators, which generalize union and intersection operators: for a number t, a t-threshold operator selects elements that appear in at least in t of the operand sets. Finally, the adaptive algorithm we provide supports union and intersection operators.

Despite its emergence more than a decade ago, information architecture remains a problematic concept. A study of relevant literature suggests significant advocacy with inadequate supporting evidence on its existence, application or value. The available limited research evidence generally presents unsatisfactory information architecture experience. Notwithstanding the unresolved issues and reported unsatisfactory experience, information architecture continues to be referenced as an important information management issue. Hence this doctoral study sought to investigate it. In the first stage, the study set out to clarify the position of information architecture via a large scale postal survey of 294 organisations. The survey found that information architecture is being used in association with IS planning, particularly in organisations which position IT as a strategic resource, but perceptions on its two conventional key components vary. While application architecture is viewed as being useful for IS planning, corporate data model is seen as being more relevant to data management and project implementation. Both models are regarded as tools facilitating integrated information systems development. In the second stage of research, case studies on 6 large organisations were conducted to gain an in-depth understanding of successful information architecture practice. The investigation reaffirmed application architecture's position as an IS planning tool and cast further doubt on corporate data model's role not only in IS planning but also in IS practice as a whole. Business area/project data model was identified as the pragmatic high-level data model for both application/database development and data management. A major finding of the case studies was on business system architecture, a pictorial model depicting IT in its business setting. It is seen as being of value for integrating IS planning with strategy development and business planning - a tool for fusing IT with the business. The case studies concluded that the value and effectiveness of information architecture is dependent on the targeting of its components - business system architecture, application architecture and business area/project data model - in terms of tasks and recipients. The case for a holistic approach to business/IS planning and implementation is currently being argued by a number of leading management and IS scholars. This thesis embraces the holistic approach and positions the (redefined) information architecture as a valuable tool in its implementation.

This thesis describes a class of problems in which interactions occur when plans to achieve members of a set of simultaneous goals are concatenated in the hope of achieving the whole goal. They will be termed "interaction problems". Several well known problems fall into this class. Swapping the values of two computer registers is a typical example. A very simple 3 block problem is used to illustrate the interaction difficulty. It is used to describe how a simple method can be employed to derive enough information from an interaction which has occurred to allow problem solving to proceed effectively. The method used to detect interactions and derive information from them, allowing problem solving to be re-directed, relies on an analysis of the goal and subgoal structure being considered by the problem solver. This goal structure will be called the "approach" taken by the system. It specifies the order in which individual goals are being attempted and any precedence relationships between them (say because one goal is a precondition of an action to achieve another). We argue that the goal structure of a problem contains information which is simpler and more meaningful than the actual plan (sequence of actions) being considered. We then show how an analysis of the goal structure of a problem, and the correction of such a structure in the light of any interaction, can direct the search towards a successful solution. Interaction problems pose particular difficulties for most current problem solvers because they achieve each part of a composite goal independently and assume that the resulting plans can be concatenated to achieve the overall goal. This assumption is beneficial in that it can drastically reduce the search necessary in many problems. However, it does restrict the range of problems which can be tackled. The problem solver, INTERPLAN, to be described as a result of this investigation, also assumes that subgoals can be solved independently, but when an interaction is detected it performs an analysis of the goal structure of the problem to re-direct the search. INTERPLAN is an efficient system which allows the class of interaction problems to be coped with. INTERPLAN uses a data structure called a "ticklist" as the basis of its mechanism for keeping track of the search it performs. The ticklist allows a very simple method to be employed for detecting and correcting for interactions by providing a summary of the goal structure of the problem being tried.

The data flow machine, which represents a radical departure from the conventional von Neumann architecture, shows great potential as a candidate for the future generation of computers. The difficulty in the usage of data structures as well as the effective exploitation of parallelism are two issues which have not as yet been fully resolved within the framework of the data flow model. / This thesis concentrates on these important problems in the following manner. Firstly, the role memory can play in a data flow system is examined. A new concept called "active memory" is introduced together with various new actors. It is shown that these enhancements make it possible to implement a limited form of shared memory which readily supports the use of data structures. / Secondly, execution performance of data flow programs is examined in the context of conditional statements. Transformations applied to the data flow graph are presented which increase the degree of parallelism. Analysis, both theoretical and empirical, is performed, showing that substantial improvements are obtained with a minimal impact on other system components.

Thesis (Ph.D.)--University of Adelaide, School of Applied Mathematics, 2002. / "November 4, 2002." Includes bibliographical references (leaves 180-814).

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 176-195.

Thesis (Ph.D.)--University of Adelaide, School of Applied Mathematics, 2002. / "November 4, 2002." Includes bibliographical references (leaves 180-814). Also available in a print format.

Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed March 17, 2009). College of Computer and Information Science. Includes bibliographical references (p. 134-140).

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Apr. 9, 2009). Includes bibliographical references.