10 research outputs found
Query Reformulation: Data Integration Approach to Multi Domain Query Answering System
Data integration gives the user with a unified view of all heterogeneous data sources. The basic service provided by data integration is query processing. Whatever query posed to the system is being given to global schema which has to reformulate to sub queries that are to be posed to the local sources. Reformulation is being accomplished by mapping between global and local sources by Global-as-View (GAV), Local-as-view (LAV) and Global-local-as-view (GLAV) approach. When a query involves multiple domains, it is difficult to extract information in case of general service engines
Information sharing agents in a peer data exchange system
We present a semantics and answer set programs for relational peer data exchange systems. When a peer answers a query, it exchanges data with other peers in order to supplement or modify its own data source. The data exchange relationships between peers are specified by logical sentences called data exchange constraints and trust relationships, which together determine how data is moved around (in order to keep them satisfied). This process determines virtual, alternative instances for a peer that can be specified as the models of an answer set program. The peer consistent answers to a query that are returned by a peer are those that are invariant under all these instances. The logic program can be used to compute peer consistent answers
Magic Sets for Disjunctive Datalog Programs
In this paper, a new technique for the optimization of (partially) bound
queries over disjunctive Datalog programs with stratified negation is
presented. The technique exploits the propagation of query bindings and extends
the Magic Set (MS) optimization technique.
An important feature of disjunctive Datalog is nonmonotonicity, which calls
for nondeterministic implementations, such as backtracking search. A
distinguishing characteristic of the new method is that the optimization can be
exploited also during the nondeterministic phase. In particular, after some
assumptions have been made during the computation, parts of the program may
become irrelevant to a query under these assumptions. This allows for dynamic
pruning of the search space. In contrast, the effect of the previously defined
MS methods for disjunctive Datalog is limited to the deterministic portion of
the process. In this way, the potential performance gain by using the proposed
method can be exponential, as could be observed empirically.
The correctness of MS is established thanks to a strong relationship between
MS and unfounded sets that has not been studied in the literature before. This
knowledge allows for extending the method also to programs with stratified
negation in a natural way.
The proposed method has been implemented in DLV and various experiments have
been conducted. Experimental results on synthetic data confirm the utility of
MS for disjunctive Datalog, and they highlight the computational gain that may
be obtained by the new method w.r.t. the previously proposed MS methods for
disjunctive Datalog programs. Further experiments on real-world data show the
benefits of MS within an application scenario that has received considerable
attention in recent years, the problem of answering user queries over possibly
inconsistent databases originating from integration of autonomous sources of
information.Comment: 67 pages, 19 figures, preprint submitted to Artificial Intelligenc
Design and development of a context sensitive rural development software application for eService provisioning
After more than a decade since South Africa realized the importance of Information and Communication Technology (ICT) and the role it can play to deliver services, the country is still confronted by a number of challenges challenges that hinder the implementation of a fully-fledged ICT-based system in a form of electronic government to better deliver services and information. While rural development remains as one of the country’s greatest concerns, ICT is among approaches and perspectives that are recognized for not only accelerating rural development but also for providing the country’s economic growth. This research was set to investigate approaches to implement ICT solutions for rural development and service provisioning in the context of electronic government. The research focused more on the technical skills to implement such ICT systems for the benefit of rural development and e-government stakeholders that have an interest in design and development of an integrated and interoperable solution to accelerate service delivery, especially in rural communities. A mixed methods approach was used throughout the research accompanied by an evolutionary prototyping to development the desired prototype. A study was then conducted to gain an understanding of the state and the needs of rural communities to date. The results of the study yielded a number of urbanized service providers that rural dwellers need to timeously visit to consume services. Scenarios to design and develop the intended prototypes were then drawn from these results. The overall implementation of the prototypes produced an integrated platform that allows multiple disparate systems to communicate, share and use information. The qualities of the prototype are what this research recommends to relevant to stakeholders in order to implement an integrated and interoperable e-government system that elevates rural development programs and service delivery
Consistent query answers in virtual data integration systems
When data sources are virtually integrated there is no common and centralized mechanism for maintaining global consistency. In consequence, it is likely that inconsistencies with respect to certain global integrity constraints (ICs) will occur. In this chapter we consider the problem of defining and computing those answers that are consistent wrt the global ICs when global queries are posed to virtual data integration systems whose sources are specified following the local-as-view approach. The solution is based on a specification using logic programs with stable model semantics of the minimal legal instances of the integration system. Apart from being useful for computing consistent answers, the specification can be used to compute the certain answers to monotone queries, and minimal answers to non monotone queries
Consistent Query Answers in Virtual Data Integration Systems
When data sources are virtually integrated there is no common and centralized mechanism for maintaining global consistency. In consequHHj9 it is likely that inconsistencies with respect to certain global integrity constraints (ICs)will occu; In this chapter we consider the problem of defining andcompu2;) those answers that are consistent wrt the global ICs when global qubal) are posed tovirtuM data integration systems whosesou)33 are specified following the local-as-view approach