Fundamentals of Physical Design and Query Compilation

Toman, David; Weddell, Grant E.

doi:10.2200/s00363ed1v01y201105dtm018

Cited by 29 publications

(41 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To identify such cases, Buil-Aranda et al introduce a notion of strong boundedness of variables in graph patterns and use it to show a notion of safeness for the evaluation of patterns like P S within larger graph patterns. The idea behind the notion of strongly bound variables has already been used in earlier work (e.g., "certain variables" [34], "output variables" [37]), and it is tempting to adopt it for our problem. To this end, we first define the notion of strongly bound variables for our PP-based graph patterns: Definition 24.…”

Section: Web-safeness Of Context-based Semanticsmentioning

confidence: 99%

SPARQL with property paths on the Web

Hartig

Pirrò

2017

View full text Add to dashboard Cite

Abstract. Linked Data on the Web represents an immense source of knowledge suitable to be automatically processed and queried. In this respect, there are different approaches for Linked Data querying that differ on the degree of centralization adopted. On one hand, the SPARQL query language, originally defined for querying single datasets, has been enhanced with features to query federations of datasets; however, this attempt is not sufficient to cope with the distributed nature of data sources available as Linked Data. On the other hand, extensions or variations of SPARQL aim to find trade-offs between centralized and fully distributed querying. The idea is to partially move the computational load from the servers to the clients. Despite the variety and the relative merits of these approaches, as of today, there is no standard language for querying Linked Data on the Web. A specific requirement for such a language to capture the distributed, graph-like nature of Linked Data sources on the Web is a support of graph navigation. Recently, SPARQL has been extended with a navigational feature called property paths (PPs). However, the semantics of SPARQL restricts the scope of navigation via PPs to single RDF graphs. This restriction limits the applicability of PPs for querying distributed Linked Data sources on the Web. To fill this gap, in this paper we provide formal foundations for evaluating PPs on the Web, thus contributing to the definition of a query language for Linked Data. We first introduce a family of reachability-based query semantics for PPs that distinguish between navigation on the Web and navigation at the data level. Thereafter, we consider another, alternative query semantics that couples Web graph navigation and data level navigation; we call it context-based semantics. Given these semantics, we find that for some PP-based SPARQL queries a complete evaluation on the Web is not possible. To study this phenomenon we introduce a notion of Web-safeness of queries, and prove a decidable syntactic property that enables systems to identify queries that are Web-safe. In addition to establishing these formal foundations, we conducted an experimental comparison of the context-based semantics and a reachability-based semantics. Our experiments show that when evaluating a PP-based query under the context-based semantics one experiences a significantly smaller number of dereferencing operations, but the computed query result may contain less solutions.

show abstract

Section: Web-safeness Of Context-based Semanticsmentioning

confidence: 99%

SPARQL with property paths on the Web

Hartig

Pirrò

2017

View full text Add to dashboard Cite

show abstract

“…The book of Toman and Weddell [18] overviews a broad approach to reformulation that maintains the logical/physical schema restriction, but adds access restrictions to the mix. A reformulation process that works for general first-order constraints is outlined, which produces a query over the physical schema, but one that may not abide by access restrictions.…”

Section: Introductionmentioning

confidence: 99%

Querying with access patterns and integrity constraints

2015

View full text Add to dashboard Cite

Traditional query processing involves a search for plans formed by applying algebraic operators on top of primitives representing access to relations in the input query. But many querying scenarios involve two interacting issues that complicate the search. On the one hand, the search space may be limited by access restrictions associated with the interfaces to datasources, which require certain parameters to be given as inputs. On the other hand, the search space may be extended through the presence of integrity constraints that relate sources to each other, allowing for plans that do not match the structure of the user query.In this paper we present the first optimization approach that attacks both these difficulties within a single framework, presenting a system in which classical cost-based join optimization is extended to support both access-restrictions and constraints. Instead of iteratively exploring subqueries of the input query, our optimizer explores a space of proofs that witness the answering of the query, where each proof has a direct correspondence with a query plan.

show abstract

“…The Byte-code compiler converts range-restricted first order formulae (both schema constraints and user queries) and generates the appropriate byte-code used by the Split Tableau VM. The Code generator converts query plans (still expressed as annotated first-order formulae) to actual imperative code, e.g., in C or LLVM (see, e.g., code fragments in [11]). The following sections now describe each of the modules.…”

Section: System Architecture and Componentsmentioning

confidence: 99%

“…The code for the plan is then a C get-first/get-next iterator representing a nested loops join applied on S and a simple complement of G, as outlined in [11].…”

Section: Query Planning and Optimizationmentioning

confidence: 99%

See 1 more Smart Citation

An Interpolation-based Compiler and Optimizer for Relational Queries (System design Report)

Toman¹,

Weddell²

Kalpa Publications in Computing

Self Cite

View full text Add to dashboard Cite

We outline the implementation of a query compiler for relational queries that generates query plans with respect to a database schema, that is, a set of arbitrary first-order constraints, and a distinguished subset of predicate symbols from the underlying signature that correspond to access paths. The compiler is based on a variant of the Craig interpolation theorem, with reasoning realized via a modified analytic tableau proof procedure. This procedure decouples the generation of candidate plans that are interpolants from the tableau proof procedure, and applies A*-based search with respect to an external cost model to arbitrate among the alternative candidate plans. The tableau procedure itself is implemented as a virtual machine that operates on a compiled and optimized byte-code that faithfully implements reasoning with respect to the database schema constraints and a user query.

show abstract

Fundamentals of Physical Design and Query Compilation

Cited by 29 publications

References 33 publications

SPARQL with property paths on the Web

SPARQL with property paths on the Web

Querying with access patterns and integrity constraints

An Interpolation-based Compiler and Optimizer for Relational Queries (System design Report)

Contact Info

Product

Resources

About