Showing papers presented at "Database Programming Languages in 2009"
20 Aug 2009
TL;DR: A framework in which query sizes can be estimated from arbitrary statistical assertions on the data, using the Entropy-Maximization probability distribution, and it is shown that several classes of statistics can be solved in closed form.
Abstract: We propose a framework in which query sizes can be estimated from arbitrary statistical assertions on the data. In its most general form, a statistical assertion states that the size of the output of a conjunctive query over the data is a given number. A very simple example is a histogram, which makes assertions about the sizes of the output of several range queries. Our model also allows much more complex assertions that include joins and projections. To model such complex statistical assertions we propose to use the Entropy-Maximization (EM) probability distribution. In this model any set of statistics that is consistent has a precise semantics, and every query has an precise size estimate. We show that several classes of statistics can be solved in closed form.
19 citations
20 Aug 2009
TL;DR: It is shown that tractability by covering DTDs is fragile against sibling axes, and that upward axes appearing in qualifiers bring intractability under even disjunction-free D TDs.
Abstract: The paper presents a tractable subclass of DTDs, called DC-DTDs, for XPath satisfiability with sibling axes. A DC-DTD is a DTD such that each content model is in the form of a concatenation of single tag names and Kleene-starred regular expressions. DC-DTDs are a proper subclass of covering DTDs proposed by Montazerian et al., and a proper superclass of disjunction-free DTDs. In this paper, it is shown that tractability by covering DTDs is fragile against sibling axes. Then, tractability of XPath satisfiability with sibling axes under DC-DTDs is demonstrated. Finally, as a limitation of the tractability of DC-DTDs, it is shown that upward axes appearing in qualifiers bring intractability under even disjunction-free DTDs.
17 citations
20 Aug 2009
TL;DR: In this article, the view-based security framework for XML without imposing any of the previously considered restrictions on the class of queries, class of DTDs, and the type of annotations used to define the view.
Abstract: In this paper, we revisit the view based security framework for XML without imposing any of the previously considered restrictions on the class of queries, the class of DTDs, and the type of annotations used to define the view. First, we show that the full class of Regular XPath queries is closed under query rewriting . Next, we address the problem of constructing a DTD that describes the view schema, which in general needs not be regular. We propose three different methods of approximating the view schema and we show that the produced DTDs are indistinguishable from the exact schema (with queries from a class specific for each method). Finally, we investigate problems of static analysis of security access specifications.
16 citations
20 Aug 2009
TL;DR: This paper investigates the problem of schema alteration, or synthesizing an output schema describing the result of an update applied to a given input schema, and develops an effect analysis and schema alteration which can be used as the basis for sound typechecking for queries involving "transform".
Abstract: The W3C recently released the XQuery Update Facility 1.0, a Candidate Recommendation for an XML update language. It appears likely that this proposal will become standard. XQuery has been equip- ped with a formal semantics and sound type system, but there has been little work on static analysis or typechecking of XML updates, and the typing rules in the current W3C proposal appear unsound for "transform" queries that perform embedded updates. In this paper, we investigate the problem of schema alteration , or synthesizing an output schema describing the result of an update applied to a given input schema. We review regular expression type systems for XQuery, present a core language and semantics for W3C-style XML updates, and develop an effect analysis and schema alteration, which can be used as the basis for sound typechecking for queries involving "transform".
20 Aug 2009
TL;DR: Regular XPath (RXPath) is presented, which is a natural extension of XPath with regular expressions over paths that has the same computational properties as XPath: linear-time query evaluation and exponential-time reasoning.
Abstract: In this paper we present Regular XPath (RXPath), which is a natural extension of XPath with regular expressions over paths that has the same computational properties as XPath: linear-time query evaluation and exponential-time reasoning. To establish these results, we devise a unifying automata-theoretic framework based on two-way weak alternating tree automata. Specifically, we consider automata that have infinite runs on finite trees. This enables us to leverage and simplify existing automata-theoretic machinery and develop algorithms both for query evaluation and for reasoning over queries. With respect to the latter problem, we consider RXPath as a constraint language, and study constraint satisfiability, and query satisfiability and containment under constraints in the setting of RXPath.
20 Aug 2009
TL;DR: This work shows how to translate expressions in a higher-order programming language into SQL queries, and shows that any suitable expression translates to a single SQL query, where the suitability is determined by a type-and-effect check.
Abstract: We show how to translate expressions in a higher-order programming language into SQL queries Somewhat surprisingly, we show that any suitable expression translates to a single SQL query, where the suitability is determined by a type-and-effect check Thus, unlike in Hollywood where a script-writer can never be sure a movie sequel will be popular, we show how to be sure that your SQL--written in your own language--will succeed (in being translated)