Tannen, Val

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  • Publication
    A Chase Too Far?
    (2000-05-01) Popa, Lucian; Deutsch, Alin; Sahuguet, Arnaud; Tannen, Val
    In a previous paper we proposed a novel method for generating alternative query plans that uses chasing (and back-chasing) with logical constraints. The method brings together use of indexes, use of materialized views, semantic optimization and join elimination (minimization). Each of these techniques is known separately to be beneficial to query optimization. The novelty of our approach is in allowing these techniques to interact systematically, e.g., nontrivial use of indexes and materialized views may be enabled only by semantic constraints. We have implemented our method for a variety of schemas and queries. We examine how far we can push the method in term of complexity of both schemas and queries. We propose a technique for reducing the size of the search space by "stratifying" the sets of constraints used in the (back)chase. The experimental results demonstrate that our method is practical (i.e., feasible and worthwhile).
  • Publication
    Polymorphic Rewriting Conserves Algebraic Confluence
    (1992) Tannen, Val; Gallier, Jean H
    We study combinations of many-sorted algebraic term rewriting systems and polymorphic lambda term rewriting. Algebraic and lambda terms are mixed by adding the symbols of the algebraic signature to the polymorphic lambda calculus, as higher-order constants. We show that if a many-sorted algebraic rewrite system R has the Church-Rosser property (is confluent), then R + β + type-β + type-η rewriting of mixed terms has the Church-Rosser property too. η reduction does not commute with algebraic reduction, in general. However, using long normal forms, we show that if R is canonical (confluent and strongly normalizing) then equational provability from R + β + η + type-β + type-η is still decidable.
  • Publication
    Annotated XML: Queries and Provenance
    (2008-06-11) Foster, John N; Green, Todd J; Tannen, Val
    We present a formal framework for capturing the provenance of data appearing in XQuery views of XML. Building on previous work on relations and their (positive) query languages, we decorate unordered XML with annotations from commutative semirings and show that these annotations suffice for a large positive fragment of XQuery applied to this data. In addition to tracking provenance metadata, the framework can be used to represent and process XML with repetitions, incomplete XML, and probabilistic XML, and provides a basis for enforcing access control policies in security applications. Each of these applications builds on our semantics for XQuery, which we present in several steps: we generalize the semantics of the Nested Relational Calculus (NRC) to handle semiring-annotated complex values, we extend it with a recursive type and structural recursion operator for trees, and we define a semantics for XQuery on annotated XML by translation into this calculus.
  • Publication
    Provenance in ORCHESTRA
    (2010-01-01) Green, Todd J; Ives, Zachary G; Karvounarakis, Grigoris; Tannen, Val
    Sharing structured data today requires agreeing on a standard schema, then mapping and cleaning all of the data to achieve a single queriable mediated instance. However, for settings in which structured data is collaboratively authored by a large community, such as in the sciences, there is seldom con- sensus about how the data should be represented, what is correct, and which sources are authoritative. Moreover, such data is dynamic: it is frequently updated, cleaned, and annotated. The ORCHESTRA collaborative data sharing system develops a new architecture and consistency model for such settings, based on the needs of data sharing in the life sciences. A key aspect of ORCHESTRA’s design is that the provenance of data is recorded at every step. In this paper we describe ORCHESTRA’s provenance model and architecture, emphasizing its integral use of provenance in enforcing trust policies and translating updates efficiently.
  • Publication
    Update Exchange With Mappings and Provenance
    (2007-11-27) Green, Todd J; Karvounarakis, Grigoris; Ives, Zachary G; Tannen, Val
    We consider systems for data sharing among heterogeneous peers related by a network of schema mappings. Each peer has a locally controlled and edited database instance, but wants to ask queries over related data from other peers as well. To achieve this, every peer’s updates propagate along the mappings to the other peers. However, this update exchange is filtered by trust conditions — expressing what data and sources a peer judges to be authoritative — which may cause a peer to reject another’s updates. In order to support such filtering, updates carry provenance information. These systems target scientific data sharing applications, and their general principles and architecture have been described in [21]. In this paper we present methods for realizing such systems. Specifically, we extend techniques from data integration, data exchange, and incremental view maintenance to propagate updates along mappings; we integrate a novel model for tracking data provenance, such that curators may filter updates based on trust conditions over this provenance; we discuss strategies for implementing our techniques in conjunction with an RDBMS; and we experimentally demonstrate the viability of our techniques in the Orchestra prototype system. This technical report supersedes the version which appeared in VLDB 2007 [17] and corrects certain technical claims regarding the semantics of our system (see errata in Sections [3.1] and [4.1.1]).
  • Publication
    Logical and Computational Aspects of Programming With Sets/Bags/Lists
    (1991-10-01) Tannen, Val; Subrahmanyam, Ramesh
    We study issues that arise in programming with primitive recursion over non-free datatypes such as lists, bags and sets. Programs written in this style can lack a meaning in the sense that their outputs may be sensitive to the choice of input expression. We are, thus, naturally led to a set-theoretic denotational semantics with partial functions. We set up a logic for reasoning about the definedness of terms and a deterministic and terminating evaluator. The logic is shown to be sound in the model, and its recursion free fragment is shown to be complete for proving definedness of recursion free programs. The logic is then shown to be as strong as the evaluator, and this implies that the evaluator is compatible with the provable equivalence between different set (or bag, or list) expressions. Oftentimes, the same non-free datatype may have different presentations, and it is not clear a priori whether programming and reasoning with the two presentations are equivalent. We formulate these questions, precisely, in the context of alternative presentations of the list, bag, and set datatypes and study some aspects of these questions. In particular, we establish back-and-forth translations between the two presentations, from which it follows that they are equally expressive, and prove results relating proofs of program properties, in the two presentations.
  • Publication
    HOLON/CADSE: Integrating Open Software Standards and Formal Methods to Generate Guideline-Based Decision Support Agents
    (1999) Silverman, Barry G; Wong, Alex; Lang, Lance; Tannen, Val; Khoury, Allan; Campbell, Keith; Sahuguet, Arnaud; Qiang, Chen
    This paper describes the efforts of a consortium that is trying to develop and validate formal methods and a meta-environment for authoring, checking, and maintaining a large repository of machine executable practice guidelines. The goal is to integrate and extend a number of open software standards so that guidelines in the meta-environment become a resource that any vendor can plug their applications into and run in their proprietary environment provided they conform to the interface standards.
  • Publication
    Inheritance as Implicit Coercion
    (1991-02-01) Tannen, Val; Coquand, Thierry; Gunter, Carl A.; Scedrov, Andre
    We present a method for providing semantic interpretations for languages with a type system featuring inheritance polymorphism. Our approach is illustrated on an extension of the language Fun of Cardelli and Wegner, which we interpret via a translation into an extended polymorphic lambda calculus. Our goal is to interpret inheritances in Fun via coercion functions which are definable in the target of the translation. Existing techniques in the theory of semantic domains can be then used to interpret the extended polymorphic lambda calculus, thus providing many models for the original language. This technique makes it possible to model a rich type discipline which includes parametric polymorphism and recursive types as well as inheritance. A central difficulty in providing interpretations for explicit type disciplines featuring inheritance in the sense discussed in this paper arises from the fact that programs can type-check in more than one way. Since interpretations follow the type-checking derivations, coherence theorems are required: that is, one must prove that the meaning of a program does not depend on the way it was type-checked. The proof of such theorems for our proposed interpretation are the basic technical results of this paper. Interestingly, proving coherence in the presence of recursive types, variants, and abstract types forced us to reexamine fundamental equational properties that arise in proof theory (in the form of commutative reductions) and domain theory (in the form of strict vs. non-strict functions).
  • Publication
    Optimization Properties for Classes of Conjunctive Regular Path Queries
    (2001-01-01) Deutsch, Alin; Tannen, Val
    We are interested in the theoretical foundations of the optimization of conjunctive regular path queries (CRPQs). The basic problem here is deciding query containment both in the absence and presence of constraints. Containment without constraints for CRPQs is EXPSPACE-complete, as opposed to only NP-complete for relational conjunctive queries. Our past experience with implementing similar algorithms suggests that staying in PSPACE might still be useful. Therefore we investigate the complexity of containment for a hierarchy of fragments of the CRPQ language. The classifying principle of the fragments is the expressivity of the regular path expressions allowed in the query atoms. For most of these fragments, we give matching lower and upper bounds for containment in the absence of constraints. We also introduce for every fragment a naturally corresponding class of constraints in whose presence we show both decidability and undecidability results for containment in various fragments. Finally, we apply our results to give a complete algorithm for rewriting with views in the presence of constraints for a fragment that contains Kleene-star and disjunction.
  • Publication
    Physical Data Independence, Constraints and Optimization with Universal Plans
    (1999-09-07) Deutsch, Alin; Popa, Lucian; Tannen, Val
    We present an optimization method and al gorithm designed for three objectives: physi cal data independence, semantic optimization, and generalized tableau minimization. The method relies on generalized forms of chase and "backchase" with constraints (dependen cies). By using dictionaries (finite functions) in physical schemas we can capture with con straints useful access structures such as indexes, materialized views, source capabilities, access support relations, gmaps, etc. The search space for query plans is defined and enumerated in a novel manner: the chase phase rewrites the original query into a "universal" plan that integrates all the access structures and alternative pathways that are allowed by appli cable constraints. Then, the backchase phase produces optimal plans by eliminating various combinations of redundancies, again according to constraints. This method is applicable (sound) to a large class of queries, physical access structures, and semantic constraints. We prove that it is in fact complete for "path-conjunctive" queries and views with complex objects, classes and dictio naries, going beyond previous theoretical work on processing queries using materialized views.