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29
Viewbased query processing: On the relationship between rewriting, answering and losslessness
, 2007
"... ..."
Views and Queries: Determinacy and Rewriting
 In PODS
, 2005
"... We investigate the question of whether a query Q can be answered using a set V of views. We first define the problem in informationtheoretic terms: we say that V determines Q if V provides enough information to uniquely determine the answer to Q. Next, we look at the problem of rewriting Q in terms ..."
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We investigate the question of whether a query Q can be answered using a set V of views. We first define the problem in informationtheoretic terms: we say that V determines Q if V provides enough information to uniquely determine the answer to Q. Next, we look at the problem of rewriting Q in terms of V using a specific language. Given a view language V and query language Q, we say that a rewriting language R is complete for VtoQ rewritings if every Q ∈Qcan be rewritten in terms of V ∈ Vusing a query in R, whenever V determines Q. While query rewriting using views has been extensively investigated for some specific languages, the connection to the informationtheoretic notion of determinacy, and the question of completeness of a rewriting language, have received little attention. In this paper we investigate systematically the notion of determinacy and its connection to rewriting. The results concern decidability of determinacy for various view and query languages, as well as the power required of complete rewriting languages. We consider languages ranging from firstorder to conjunctive queries. 1.
On Containment of Conjunctive Queries with Arithmetic Comparisons
 Advances in Database Technology  EDBT
, 2004
"... We study the following problem: how to test if Q2 is contained in Q1, where Q1 and Q2 are conjunctive queries with arithmetic comparisons? This problem is fundamental in a large variety of database applications. Existing algorithms first normalize the queries, then test a logical implication using m ..."
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We study the following problem: how to test if Q2 is contained in Q1, where Q1 and Q2 are conjunctive queries with arithmetic comparisons? This problem is fundamental in a large variety of database applications. Existing algorithms first normalize the queries, then test a logical implication using multiple containment mappings from Q1 to Q2. We are interested in cases where the containment can be tested more efficiently. This work aims to (a) reduce the problem complexity from PgrP2completeness to NPcompleteness in these cases; (b) utilize the advantages of the homomorphism property (i.e., the containment test is based on a single containment mapping) in applications such as those of answering queries using views; and (c) observing that many real queries have the homomorphism property. The following are our results. (1) We show several cases where the normalization step is not needed, thus reducing the size of the queries and the number of containment mappings. (2) We develop an algorithm for checking various syntactic conditions on queries, under which the homomorphism property holds. (3) We further reduce the conditions of these classes using practical domain knowledge that is easily obtainable. (4) We conducted experiments on real queries, and show that most of the queries pass this test.
Information Integration and Incomplete Information
"... We first briefly review relational databases and incomplete information. We then describe how querying in Information Integration Systems amounts to querying incomplete databases. We also discuss query rewriting, which essentially is a (compiletime) query optimization technique used in processing q ..."
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We first briefly review relational databases and incomplete information. We then describe how querying in Information Integration Systems amounts to querying incomplete databases. We also discuss query rewriting, which essentially is a (compiletime) query optimization technique used in processing queries in Information Integration systems. Finally, we review some recent advances in query rewriting.
Rewriting queries using views in the presence of arithmetic comparisons
 Information and Computer Science
, 2002
"... We consider the problem of answering queries using views, where queries and views are conjunctive queries with arithmetic comparisons over dense orders. Previous work only considered limited variants of this problem, without giving a complete solution. We first show that obtaining equivalent rewriti ..."
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We consider the problem of answering queries using views, where queries and views are conjunctive queries with arithmetic comparisons over dense orders. Previous work only considered limited variants of this problem, without giving a complete solution. We first show that obtaining equivalent rewritings for conjunctive queries with arithmetic comparisons is decidable. Then we consider the problem of finding maximally contained rewritings (MCR) where the decidability proof does not carry over. We investigate two special cases of this problem where the query uses only semiinterval comparisons. In both cases decidability of finding MCRs depends on the query containment test. First, we address the case where the homomorphism property holds in testing query containment. In this case decidability is easy to prove but developing an efficient algorithm is not trivial. We develop such an algorithm and prove that it is sound and complete. This algorithm applies in many cases where the query uses only left (or right) semiinterval comparisons. Then we develop a new query containment test for the case where the containing query uses both left and right semiinterval comparisons but with only one left (or right) semi interval subgoal. Based on this test, we show how to produce an MCR which is a Datalog query with arithmetic comparisons. The containment test that we develop obtains a result of independent interest. It finds another special case where query containment in the presence of arithmetic comparisons can be tested in nondeterministic polynomial time. 1
Logical Data Expiration
"... Data expiration is an essential component of data warehousing solutions: whenever large amounts of data are repeatedly collected over a period of time, it is essential to have a clear approach to identifying parts of the data nolonger needed and a policy that allows disposing and/or archiving these ..."
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Cited by 5 (3 self)
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Data expiration is an essential component of data warehousing solutions: whenever large amounts of data are repeatedly collected over a period of time, it is essential to have a clear approach to identifying parts of the data nolonger needed and a policy that allows disposing and/or archiving these parts of the data. Such policies are necessary even if adding storage to accommodate an evergrowing collection of data were possible, since the growing amount of data needs to be examined during querying and in turn leads to deterioration of query performance over time. The approaches
A comparison of the
 MPCP, DPCP, FMLP, on LITMUS RT (in submission
, 2008
"... queries using views in the presence of arithmetic ..."
Query Answering using Views in the Presence of Dependencies ABSTRACT
"... In this paper we investigate equivalent and maximally contained rewritings of a query using views under a set of dependencies. We propose two new algorithms that find equivalent and maximally contained rewritings in the presence of dependencies, and we also prove that a maximally contained rewriting ..."
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In this paper we investigate equivalent and maximally contained rewritings of a query using views under a set of dependencies. We propose two new algorithms that find equivalent and maximally contained rewritings in the presence of dependencies, and we also prove that a maximally contained rewriting computes all the certain answers under the open world assumption, both in the presence and the absence of dependencies. 1.
Finding equivalent rewritings in the presence of arithmetic comparisons
 In EDBT
, 2006
"... Abstract. The problem of rewriting queries using views has received significant attention because of its applications in a wide variety of datamanagement problems. For selectprojectjoin SQL (a.k.a. conjunctive) queries and views, there are efficient algorithms in the literature, which find equival ..."
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Abstract. The problem of rewriting queries using views has received significant attention because of its applications in a wide variety of datamanagement problems. For selectprojectjoin SQL (a.k.a. conjunctive) queries and views, there are efficient algorithms in the literature, which find equivalent and maximally contained rewritings. In the presence of arithmetic comparisons (ACs) the problem becomes more complex. We do not know how to find maximally contained rewritings in the general case. There are algorithms which find maximally contained rewritings only for special cases such as when ACs are restricted to be semiinterval. However, we know that the problem of finding an equivalent rewriting (if there exists one) in the presence of ACs is decidable, yet still doubly exponential. This complexity calls for an efficient algorithm which will perform better on average than the complete enumeration algorithm. In this work we present such an algorithm which is sound and complete. Its efficiency lies in that it considers fewer candidate rewritings because it includes a preliminary test to decide for each view whether it is potentially useful in some rewriting. 1
Answering Queries Using Views in the Presence of Functional Dependencies
 In: Proceeding of BNCOD 2005
, 2005
"... Abstract. This paper is concerned with the problem of answering queries using views in the presence of functional dependencies. Previous algorithms for answering queries using views, such as the MiniCon algorithm, have not taken into account the presence of functional dependencies. As a consequence ..."
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Abstract. This paper is concerned with the problem of answering queries using views in the presence of functional dependencies. Previous algorithms for answering queries using views, such as the MiniCon algorithm, have not taken into account the presence of functional dependencies. As a consequence, these algorithms may miss query rewritings in the presence of such dependencies. In this paper, we present an extension of the MiniCon algorithm to handle the presence of functional dependencies while still retaining the main properties of the algorithm and its computational advantage over the other algorithms. 1