XML-Based RDF Query Language (XRQL) and its Implementation

Resource Description Framework (RDF) is a language which represents information about resources. In order to search RDF resource descriptions, several RDF query languages such as RQL and SquishQL have been proposed. However, these RDF query languages do not use XML syntax and they have limited functionality. xRQL is proposed to solve these issues by defining an XML-based RDF query language with enhanced manipulations of the RDF metadata. xRQL is a logic language relying on a functional approach. It consists of an operator declaration, a RDF data description and a result description. Based on RDF graph data model, xRQL defines a graphical path expression with variables, which is similar to GOQL for describing RDF data. It also adopts the object-oriented model for creation, modification and deletion operations of RDF data. Users can define their favorite XMLcompliant result descriptions by themselves, which is similar to XQuery. In addition, a set of RDF operations for RDF schema is defined to manipulate the class and property hierarchies in RDF schema. xRQL has been implemented as an RDF query language over a native RDF database management system. This paper also briefly describes the implementation status.