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Relational Languages for Metadata Integration
 ACM Trans. Database Syst
"... In this article, we develop a relational algebra for metadata integration, Federated Interoperable Relational Algebra (FIRA). FIRA has many desirable properties such as compositionality, closure, a deterministic semantics, a modest complexity, support for nested queries, a subalgebra equivalent to c ..."
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Cited by 22 (5 self)
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In this article, we develop a relational algebra for metadata integration, Federated Interoperable Relational Algebra (FIRA). FIRA has many desirable properties such as compositionality, closure, a deterministic semantics, a modest complexity, support for nested queries, a subalgebra equivalent to canonical Relational Algebra (RA), and robustness under certain classes of schema evolution. Beyond this, FIRA queries are capable of producing fully dynamic output schemas, where the number of relations and/or the number of columns in relations of the output varies dynamically with the input instance. Among existing query languages for relational metadata integration, only FIRA provides generalized dynamic output schemas, where the values in any (fixed) number of input columns can determine output schemas. Further contributions of this article include development of an extended relational model for metadata integration, the Federated Relational Data Model, which is strictly downward compatible with the relational model. Additionally, we define the notion of Transformational Completeness for relational query languages and postulate FIRA as a canonical transformationally complete language. We also give a declarative, SQLlike query language that is equivalent to FIRA, called Federated Interoperable Structured Query Language (FISQL). While our main contributions are conceptual, the federated model, FISQL/FIRA, and the notion of transformational completeness nevertheless have important applications to data integration and OLAP. In addition to summarizing these applications, we illustrate the use of FIRA to optimize FISQL queries using rulebased transformations that directly parallel their canonical relational counterparts. We conclude the article with an extended discussion of related work as well as an indication of current and future work on FISQL/FIRA.
Towards a Type Discipline for Answer Set Programming
"... Abstract. We argue that it is high time that types had a beneficial impact in the field of Answer Set Programming and in particular Disjunctive Datalog as exemplified by the DLV system. Things become immediately more challenging, as we wish to present a type system for DLVComplex, an extension of D ..."
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Abstract. We argue that it is high time that types had a beneficial impact in the field of Answer Set Programming and in particular Disjunctive Datalog as exemplified by the DLV system. Things become immediately more challenging, as we wish to present a type system for DLVComplex, an extension of DLV with uninterpreted function symbols, external implemented predicates and types. Our type system owes to the seminal polymorphic type system for Prolog introduced by Mycroft and O’Keefe, in the formulation by Lakshman and Reddy. The most innovative part of the paper is developing a declarative grounding procedure which is at the same time appropriate for the operational semantics of ASP and able to handle the new features provided by DLVComplex. We discuss the soundness of the procedure and evaluate informally its success in reducing, as expected, the set of ground terms. This yields an automatic reduction in size and numbers of (non isomorphic) models. Similar results could have only been achieved in the current untyped version by careful use of generator predicates in lieu of types.
The Complexity of Higherorder Queries
"... Higherorder transformations are ubiquitous within data management. In relational databases, higherorder queries appear in numerous aspects including query rewriting and query specification. This work investigates languages that combine higherorder transformations with ordinary relational databas ..."
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Higherorder transformations are ubiquitous within data management. In relational databases, higherorder queries appear in numerous aspects including query rewriting and query specification. This work investigates languages that combine higherorder transformations with ordinary relational database query languages. We study the two most basic computational problems associated with these query languages – the evaluation problem and the containment problem. We isolate the complexity of evaluation at every order, in an analysis similar to that for that standard typed lambda calculus. We show that the containment problem (and hence, the equivalence problem) is decidable in several important subcases, particularly in the case where query constants and variables range over the positive relational operators. The main decidability result relies on techniques that differ from those used in classical query containment. We also show that the analysis of higherorder queries is closely connected to the evaluation and containment problems for nonrecursive Datalog. 1.
DNAQL: A QUERY LANGUAGE FOR DNA STICKER COMPLEXES
"... Abstract. DNA computing has a rich history of computing paradigms with great expressive power. However, far less expressive power is needed for data manipulation. Indeed, the relational algebra, the yardstick of database systems, is expressible in firstorder logic, and thus less powerful than Turin ..."
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Abstract. DNA computing has a rich history of computing paradigms with great expressive power. However, far less expressive power is needed for data manipulation. Indeed, the relational algebra, the yardstick of database systems, is expressible in firstorder logic, and thus less powerful than Turingcomplete models. Turingcomplete DNA computing models have to account for many and varied scenarios. A DNA implementation of data manipulations might be nimbler and perform its operation faster than a Turingcomplete DNA computing model. Hence, we propose a restrictive model for implementing data manipulation operations, focused on implementability in DNA. We call this model the sticker complex model. A forte of the sticker complex model, is its ability to detect when hybridization becomes an uncontrolled chain reaction. Such chain reactions make hybridization less predictable and thus less attractive for deterministic computations. Next, we defined a query language on sticker complexes, called DNAQL. DNAQL is a typed, applicative functional programming language, powerful enough to simulate the relational algebra on sticker complexes. The type system enjoys a number of desirable properties such as soundness, maximality, and tightness. Key words. model, DNAQL
Verification, Theory, Languages
"... Complex database queries, like programs in general, can ‘crash’, i.e., can raise runtime errors. We want to avoid crashes without losing expressive power, or we want to correctly predict the absence of crashes. We show how concepts and techniques from programming language theory, notably type system ..."
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Complex database queries, like programs in general, can ‘crash’, i.e., can raise runtime errors. We want to avoid crashes without losing expressive power, or we want to correctly predict the absence of crashes. We show how concepts and techniques from programming language theory, notably type systems and reflection, can be adapted to this end. Of course, the specific nature of database queries (as opposed to general programs), also requires some new methods, and raises new questions.
Acta Informatica manuscript No.
"... (will be inserted by the editor) On the complexity of deciding typability in the relational algebra ..."
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(will be inserted by the editor) On the complexity of deciding typability in the relational algebra