A methodology for coupling fragments of XPath with structural indexes for XML documents

Semantic Search Over the Web

et al. 2012

In this chapter we present a general survey of the current state of the art in RDF storage and indexing. In the flurry of research on RDF data management in the last decade, we can identify three different perspectives on RDF: (1) a relational perspective; (2) an entity perspective; and (3) a graph-based perspective. Each of these three perspectives has drawn from ideas and results in three distinct research communities to propose solutions for managing RDF data: relational databases (for the relational perspective); information retrieval (for the entity perspective); and graph theory and graph databases (for the graph-based perspective). Our goal in this chapter is to give an up-to-date overview of represpentative solutions within each perspective.

Section: Structural Indexessupporting

confidence: 73%

Storing and Indexing Massive RDF Datasets

Luo

Picalausa

Semantic Search Over the Web

et al. 2012

“…Tarski's algebra is a fundamental tool in the field of algebraic logic which finds various applications in computer science [3][4][5][6]. Our investigation is specifically motivated by the role the relation algebra plays in the study of database query languages [7][8][9][10][11][12][13]. In particular, the algebras we consider in this paper correspond to natural fragments of XPath.…”

Section: Introductionmentioning

confidence: 99%

“…This feasibility hints towards efficient partitioning and reduction techniques on both the set of nodes and the set of paths in a document. Such techniques may fruitfully applied towards, e.g., document compression [27], access control [28], and designing indexes for query processing [12,29,30].…”

Section: Introductionmentioning

confidence: 99%

Structural characterizations of the navigational expressiveness of relation algebras on a tree

Journal of Computer and System Sciences

Gyssens

Paredaens

et al. 2016

Self Cite

Given a document D in the form of an unordered node-labeled tree, we study the expressiveness on D of various basic fragments of XPath, the core navigational language on XML documents. Working from the perspective of these languages as fragments of Tarski's relation algebra, we give characterizations, in terms of the structure of D, for when a binary relation on its nodes is definable by an expression in these algebras. Since each pair of nodes in such a relation represents a unique path in D, our results therefore capture the sets of paths in D definable in each of the fragments. We refer to this perspective on language semantics as the "global view." In contrast with this global view, there is also a "local view" where one is interested in the nodes to which one can navigate starting from a particular node in the document. In this view, we characterize when a set of nodes in D can be defined as the result of applying an expression to a given node of D. All these definability results, both in the global and the local view, are obtained by using a robust two-step methodology, which consists of first characterizing when two nodes cannot be distinguished by an expression in the respective fragments of XPath, and then bootstrapping these characterizations to the desired results.Keywords: trees, relation algebra, XML, XPath, bisimulation, instance expressivity $ A preliminary version of some of the results given here were presented at the Twenty-Fifth ACM Symposium on Principles of Database Systems [1].

“…Hence, a notion of localized k-bisimulation has proven to be quite successful in data management applications (e.g., [11,17,26,32]). k-bisimulation is the variant of bisimulation where topological features of nodes are only considered within a local neighborhood of radius k 0.…”

Section: Introductionmentioning

confidence: 99%

External memory K-bisimulation reduction of big graphs

Luo

Proceedings of the 22nd ACM International Conference on Information &Amp; Knowledge Management

Hidders

et al. 2013

Self Cite

In this paper, we present, to our knowledge, the first known I/O efficient solutions for computing the k-bisimulation partition of a massive directed graph, and performing maintenance of such a partition upon updates to the underlying graph. Ubiquitous in the theory and application of graph data, bisimulation is a robust notion of node equivalence which intuitively groups together nodes in a graph which share fundamental structural features. kbisimulation is the standard variant of bisimulation where the topological features of nodes are only considered within a local neighborhood of radius k 0.The I/O cost of our partition construction algorithm is bounded by O(k · sort(|Et|) + k · scan(|Nt|) + sort(|Nt|)), while our maintenance algorithms are bounded by O(k · sort(|Et|) + k · sort(|Nt|)). The space complexity bounds are O(|Nt| + |Et|) and O(k · |Nt| + k · |Et|), resp. Here, |Et| and |Nt| are the number of disk pages occupied by the input graph's edge set and node set, resp., and sort(n) and scan(n) are the cost of sorting and scanning, resp., a file occupying n pages in external memory. Empirical analysis on a variety of massive real-world and synthetic graph datasets shows that our algorithms perform efficiently in practice, scaling gracefully as graphs grow in size.