Tech Reports in Computer Science and Engineering

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    Amalgamating Knowledge Bases, II - Distributed Mediators
    (1998-10-15) Adali, Sibel; Subrahmanian, V.S.
    Integrating knowledge from multiple sources is an important aspect of automated reasoning systems.In previous work, we presented a uniform declarative and operational framework, based on annotated logics, for amalgamating multiple knowledge bases and data structures (e.g. relational, object-oriented, spatial, and temporal structures) when these knowledge bases (possibly) contain inconsistencies, uncertainties, and non-monotonic modes of negation. We showed that annotated logics may be used, with some modifications, to mediate between different knowledge bases. The multiple knowledge bases are amalgamated by embedding the individual knowledge bases into a lattice. In this paper, we describe how, given a network of sites where the different databases reside, it is possible to define a distributed semantics for amalgamated knowledge bases. More importantly, we study how the mediator may be distributed across multiple sites so that when certain conditions are satisfied, network failures do not affect the end results of queries that a user may pose. We specify different ways of distributing the mediator to protect against different types of network link failures and develop alternative soundness and completeness results. (Also cross-referenced as UMIACS-TR-93-81)
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    Amalgamating Knowledge Bases, III - Algorithms, Data Structures, and Query Processing
    (1998-10-15) Adali, Sibel; Subrahmanian, V.S.
    Integrating knowledge from multiple sources is an important aspect of automated reasoning systems. In the first part of this series of papers, we presented a uniform declarative framework, based on annotated logics, for amalgamating multiple knowledge bases when these knowledge bases (possibly) contain inconsistencies, uncertainties, and non-monotonic modes of negation. We showed that annotated logics may be used, with some modifications, to mediate between different knowledge bases. The multiple knowledge bases are amalgamated by embedding the individual knowledge bases into a lattice. In this paper, we briefly describe an SLD-resolution based proof procedure that is sound and complete w.r.t. our declarative semantics. We will then develop an OLDT -resolution based query processing procedure, MULTI-OLDT , that satisfies two important properties: (1) efficient reuse of previous computations is achieved by maintaining a table -- we describe the structure of this table and show that table operations can be efficiently executed, and (2) approximate, interruptable query answering is achieved, i.e. it is possible to obtain an ``intermediate, approximate'' answer from the query processing procedure by interrupting it at any point in time during its execution. The design of the MULTI-OLDT procedure will include the development of run-time algorithms to incrementally and efficiently update the table. (Also cross-referenced as UMIACS-TR-94-35)