W3C Semantic Web Framework
The Semantic web – collaborative effort led by W3C – provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries. It is also about language for recording how the data relates to real world objects.
The Semantic Web involves the following technologies:
- A global naming scheme (Uniform Resource Identifiers or URIs)
- A standard syntax for describing data (Resource Description Framework or RDF)
- A standard means of describing the properties of that data (RDF Schema or RDF-S)
- A standard means of describing relationships between data items (Ontology – OWL)
RDF identifies things using Web identifiers (URIs), and describes resources in terms of simple properties and property values. Any expression in RDF is a collection of triples, each consisting of a subject (node), a predicate (relationship) and an object (node). A set of such triples is called an RDF graph. Detailed explanation of RDF graphs available at http://www.w3.org/TR/rdf-concepts/#ref-rdf-semantics.
RDF Schema (a semantic extension of RDF) provides mechanisms to describe groups of related resources and the relationships between those resources. The RDF vocabulary description language describes properties in terms of which classes of resource that the properties apply to.
The OWL Web Ontology Language is designed so that the information instead of just presented to humans can be processed by applications. The Semantic Web builds on XML’s ability to define customized tagging schemes and RDF’s flexible approach to representing data.
OWL has more facilities for expressing meaning and semantics than XML, RDF, and RDF-S. For example, OWL could be used to state that the childOf property is the inverse of the parentOf property. The purpose is to be more intuitively usable and support automatic text analysis and artificial intelligence applications.
SPARQL (pronounced “Sparkle”) RDF Query Language (developed by W3C) can be used to express queries across diverse data sources, whether the data is stored natively as RDF or viewed as RDF via middleware. SPARQL contains capabilities for querying required as well as optional graph patterns along with their conjunctions and disjunctions. SPARQL also supports extensible value testing and constraining queries by source RDF graph. The results of SPARQL queries can be results sets or RDF graphs.
GRDDL (developed by W3C) is a mechanism for Gleaning Resource Descriptions from Dialects of Languages. GRDDL introduces markup based on existing standards for declaring that an XML document includes data compatible with the RDF and for linking to algorithms (typically represented in XSLT), for extracting this data from the document.
Semantic technologies provide an abstraction layer above existing IT technology, enabling bridging and interconnection of data, content and processes across business and IT. Compared to traditional point-to-point integration approach, semantic portals can provide far more intelligent, relevant, and contextually aware interactions.
Graph databases – embracing RDF and SPARQL of W3C – can be said to the only standardized NoSQL solutions available today providing interoperability and porting opportunities.