Semantic querying of tree-structured data sources using partially specified tree patterns

Abstract

Nowadays, huge volumes of data are organized or exported in a tree-structured form. Querying capabilities are provided through queries that are based on branching path expression. Even for a single knowledge domain structural differences raise difficulties for querying data sources in a uniform way. In this paper, we present a method for semantically querying tree-structured data sources using partially specified tree patterns. Based on dimensions which are sets of semantically related nodes in tree structures, we define dimension graphs. Dimension graphs can be automatically extracted from trees and abstract their structural information. They are semantically rich constructs that support the formulation of queries and their efficient evaluation. We design a tree-pattern query language to query multiple treestructured data sources. A central feature of this language is that the structure can be specified fully, partially, or not at all in the queries. Therefore, it can be used to query multiple trees with structural differences. We study the derivation of structural expressions in queries by introducing a set of inference rules for structural expressions. We define two types of query unsatisfiability and we provide necessary and sufficient conditions for checking each of them. Our approach is validated through experimental evaluation.

Semantic Integration of Schema Conforming XML Data Sources

“…Users posing queries have the flexibility to specify structural constraints fully, partially or not at all. Our approach was initially developed for arbitrarily structured data sources [1]. Here, we show how this approach can be applied to tree-structured data sources that comply to schemas.…”

Containment of Partially Specified Tree-Pattern Queries

“…We present in this section our data model and query language initially introduced in [18]. The data model represents tree-structured data using the concepts of value tree, dimension and dimension graph.…”

“…In [18], necessary and sufficient conditions for query unsatisfiability are provided. In the following, we assume that queries are satisfiable with respect to G.…”

“…Their failure to provide efficient answers when applied to the problems above has motivated recently the proposal of query languages that combine keyword-based search and structured querying [12]. In [17,18] we introduce a query language that provides partial specification of a tree-pattern. A central feature of this language is that the structure can be specified fully, partially, or not at all in a query while returning structured answers.…”

“…This flexibility in specifying queries allows addressing the aforementioned problems efficiently, because only those precedence relationships that are known to hold on the data sources or that are required need to be specified in a query. On the other hand, processing these queries becomes more involved because new precedence relationships and node sharing expressions can be derived from those explicitly specified in a query [18].…”