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Determining Relevance of Accesses at Runtime
"... Consider the situation where a query is to be answered using Web sources that restrict the accesses that can be made on backend relational data by requiring some attributes to be given as input of the service. The accesses provide lookups on the collection of attributes values that match the binding ..."
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Cited by 14 (9 self)
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Consider the situation where a query is to be answered using Web sources that restrict the accesses that can be made on backend relational data by requiring some attributes to be given as input of the service. The accesses provide lookups on the collection of attributes values that match the binding. They can differ in whether or not they require arguments to be generated from prior accesses. Prior work has focused on the question of whether a query can be answered using a set of data sources, and in developing static access plans (e.g., Datalog programs) that implement query answering. We are interested in dynamic aspects of the query answering problem: given partial information about the data, which accesses could provide relevant data for answering a given query? We consider immediate and long-term notions of “relevant accesses”, and ascertain the complexity of query relevance, for both conjunctive queries and arbitrary positive queries. In the process, we relate dynamic relevance of an access to query containment under access limitations and characterize the complexity of this problem; we produce several complexity results about containment that are of interest by themselves.
Efficient maintenance techniques for views over active documents
- In International Conference on Extending Database Technology (EDBT
, 2009
"... Many Web applications are based on dynamic interactions between Web components exchanging flows of information. Such a situation arises for instance in mashup systems or when monitoring distributed autonomous systems. Our work is in this challenging context that has generated recently a lot of atten ..."
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Many Web applications are based on dynamic interactions between Web components exchanging flows of information. Such a situation arises for instance in mashup systems or when monitoring distributed autonomous systems. Our work is in this challenging context that has generated recently a lot of attention; see Web 2.0. We introduce the axlog formal model for capturing such interactions and show how this model can be supported efficiently. The central component is the axlog widget defined by one tree-pattern query or more, over an active document (in the Active XML style) that includes some input streams of updates. A widget generates a stream of updates for each query, the updates that are needed to maintain the view corresponding to the query. We exploit an array of known technologies: datalog optimization techniques such as Differential or MagicSet, constraint query languages, and efficient XML filtering (YFilter). The novel optimization technique we propose is based on fundamental new notions: a relevance (different than that of MagicSet), satisfiability and provenance for active documents. We briefly discuss an implementation of an axlog engine, an application that we used to test the approach, and results of experiments. 1.
Rewrite-Based Verification of XML Updates
, 2010
"... We propose a model for XML update primitives of the W3C XQuery Update Facility as parameterized rewriting rules of the form: ”insert an unranked tree from a regular tree language L as the first child of a node labeled by a”. For these rules, we give type inference algorithms, considering types defin ..."
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We propose a model for XML update primitives of the W3C XQuery Update Facility as parameterized rewriting rules of the form: ”insert an unranked tree from a regular tree language L as the first child of a node labeled by a”. For these rules, we give type inference algorithms, considering types defined by several classes of unranked tree automata. These type inference algorithms are directly applicable to XML static typechecking, which is the problem of verifying whether, a given document transformation always converts source documents of a given input type into documents of a given output type. We show that typechecking for arbitrary sequences of XML update primitives can be done in polynomial time when the unranked tree automaton defining the output type is deterministic and complete, and that it is EXPTIME-complete otherwise. We then apply the results to the verification of access control policies for XML updates. We propose in particular a polynomial time algorithm for the problem of local consistency of a policy, that is, for deciding the non-existence of a sequence of authorized update operations starting from a given document that simulates a forbidden update operation.
On the Equivalence of Distributed Systems with Queries and Communication
- INTERNATIONAL CONFERENCE ON DATABASE THEORY
, 2011
"... Distributed data management systems consist of peers that store, exchange and process data in order to collaboratively achieve a common goal, such as evaluate some query. We study the equivalence of such systems. We model a distributed system by a collection of Active XML documents, i.e., trees augm ..."
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Cited by 5 (2 self)
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Distributed data management systems consist of peers that store, exchange and process data in order to collaboratively achieve a common goal, such as evaluate some query. We study the equivalence of such systems. We model a distributed system by a collection of Active XML documents, i.e., trees augmented with function calls for performing tasks such as sending, receiving and querying data. As our model is quite general, the equivalence problem turns out to be undecidable. However, we exhibit several restrictions of the model, for which equivalence can be effectively decided. We also study the computational complexity of the equivalence problem, and present an axiomatization of equivalence, in the form of a set of equivalence-preserving rewrite rules allowing us to optimize a system by rewriting it into an equivalent, but possibly more efficient system.
On the optimality of top-k algorithms for interactive Web applications
- In WebDB
, 2011
"... In an interactive Web application, the application state changes according to user choices/actions. To assist users in their interaction with such applications, there is a need to provide them with recommendations for the top-k (according to some ranking metric) interactions. These recommendations m ..."
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In an interactive Web application, the application state changes according to user choices/actions. To assist users in their interaction with such applications, there is a need to provide them with recommendations for the top-k (according to some ranking metric) interactions. These recommendations must be continually updated, as the user interacts with the application, to be consistent with the actual choices she makes. Efficiency of computation is critical here to provide fast response time and a pleasant user experience. This paper establishes formal foundations for measuring the optimality of top-k algorithms of the aforementioned type, i.e. how well they perform relative to other algorithms, with respect to all possible input instances. We define several intuitive notions of optimality in this setting, analyze the fundamental difficulties in obtaining optimal algorithms, and identify conditions under which such algorithms exist. 1.
Author manuscript, published in "IEEE Data Eng. Bull. (2009)" Searching Shared Content in Communities with the Data Ring
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Project-Team gemo Management of Data and Knowledge Distributed Over the Web
"... c t i v it y e p o r t 2009 Table of contents ..."
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