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Recent Submissions

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    Introducing a multi-dimensional user model to tailor natural language generation
    (University of Waterloo, 1991-04) Chu, J.
    Previous work has shown that it is important to include user modelling in question answering systems in order to tailor the output. In this thesis, we develop a natural language response generation model that handles both definitional and procedural questions, and employs a multi-dimensional user model. The various attributes of the user recorded in the user model include the user's role, domain knowledge, preferences, interests, receptivity and memory capability. We also address how to represent the user's view of a knowledge base to then tailor generation to that user's view, and introduce a representation for knowledge bases with property inheritance based on the Telos system. We further specify how this multi-dimensional user model influences different stages of McKeown style generation, on determining question type, deciding relevant knowledge, selecting schema, instantiating predicates, and selecting predicates. An algorithm is proposed to describe how the generation process can be tailored according to these influences, and some examples are presented to show that the output is desirable. We also address the problem of conflicts arising from the variation in response generation suggested by different user model attributes and use various weighting schemes to resolve them. Furthermore, we include a procedure for updating the user model after each interaction which also enables the algorithm to be used over multiple sessions, with up-to-date information about the users.
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    Probabilistic complexity classes
    (University of Waterloo, 1991-03) Lopez-Ortiz, A.
    The purpose of this work is to present an overview of the class of problems solvable in probabilistic polynomial time with double sided error (PP). We explore the relationship of PP to other complexity classes, in particular NP and the polynomial hierarchy, and discuss closure under some standard operations such as intersection and complementation. New proofs are given of some results from the literature using techniques developed by the author.
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    Reducing communication to a buffer and queue model
    (University of Waterloo, 1991-03) Hong, James W.; Black, James P.
    In our work, we seek to reduce the communication problem to its critical concepts and build a simple, efficient, and general communication paradigm based on these concepts. We present the Buffer and Queue Model, which contains a set of communication abstractions and primitives which is simple and general, rigorous and flexible, low-level and extensible. We show how this model seeks to utilize the efficiencies of shared memory communication while providing a universal communications interface between various types of entities across a wide spectrum of environments. We give examples of how various complex communication facilities may be developed from this low-level communication system.
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    Preconditioned conjugate gradient methods for incompressible Navier-Stokes equations
    (University of Waterloo, 1991-01) Chin, P.; D'Azevedo, E. F.; Forsyth, P. A.; Tang, W.-P.
    A robust technique for solving primitive-variable formulations of the incompressible Navier-Stokes equations is to use Newton iteration for the fully-implicit nonlinear equations. A direct sparse matrix method can be used to solve the Jacobian but is costly for large problems; an alternative is to use an iterative matrix-method. This paper investigates effective ways to use a conjugate gradient type method with an incomplete LU factorization preconditioner for two-dimensional incompressible viscous oow problems. Special attention is paid to the ordering of unknowns, with emphasis on a minimum updating matrix (MUM) ordering. Numerical results are given for several test problems.
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    Reasing about equations and functional dependencies on complex objects
    (University of Waterloo, 1990) Bommel, M.F. van; Weddell, G.E.
    Virtually all semantic or object-oriented data models assume objects have an identity separate from any of their parts, and allows users to define complex object types in which part values may be any other object. This often results in a choice of query language in which a user can express navigating from one object to another by following a property value path. In this paper, we consider a constraint language in which one may express equations and functional dependencies over complex object types. The language is novel in the sense that component attributes of individual constraints may correspond to property paths. The kind of equations we consider are also important since they are a natural abstraction of the class of conjunctive queries for query languages which support property value navigation. In our introductory comments, we give an example of such a query, and outline two applications of the constraint theory to problems relating to a choice of access plan for the query. We present a sound and complete axiomatization of the constraint language for the case in which interpretations are permitted to be infinite, where interpretations themselves correspond to a form of directed labeled graph. Although the implication problem for our form of equational constraint alone over arbitrary schema is undecidable, we present decision procedures for the implication problem for both kinds of constraints when the problem scheme satisfies a stratification condition, and when all input functional dependencies are keys.