About RDF query

1. http://www.w3.org/2001/11/13-RDF-Query-Rules/
This document provides a survey of RDF query language and implementations and describes their capabilities in terms described in RDF Query and Rules Framework.

2.SPARQL: A query platform for Web 2.0 and the Semantic Web

A full list of different query language implementations can bee seen at http://www.w3.org/2001/11/13-RDF-Query-Rules/. But these languages lack both a common syntax and a common semantics. In fact, the existing query languages cover a significant semantic range: from declarative, SQL-like languages, to path languages, to rule or production-like systems. And SPARQL had to fill this gap.