Grid Computing 7700 Fall 2005 Lecture 18: Semantic Grid Gabrielle Allen allen@bit.csc.lsu.edu http://www.cct.lsu.edu/~gallen

Examples

Examples/Motivation

XML XML defines a grammar for documents but does not carry information to understand the grammar (semantic information). Different grammars can define the same content: “Gabrielle Allen is the lecturer for CS7700” Semantics come from outside the XML document <lecturer> <course>CS7700</course> <name>Gabrielle Allen</name> </lecture> <course name=“CS7700”> <lecturer>Gabrielle Allen</lecturer> </course> <course name=“CS7700” lecturer=“Gabrielle Allen” />

Semantic Web “The Semantic Web is the representation of data on the World Wide Web. It is a collaborative effort led by W3C with participation from a large number of researchers and industrial partners. It is based on the Resource Description Framework (RDF), which integrates a variety of applications using XML for syntax and URIs for naming.”

Semantic Grid

DefinitionsXML Defines the syntax for structured documents. XML Schema Defines rules for XML dialects (SVG, GML, etc.) and also built-in data types. RDF A data model definition language with XML bindings RDF Schema A way to define RDF-based languages (DAML-OIL, OWL). OWL An extension of RDF/RDFS with extensive property/relationship definitions for expressing logical relationships.

Annoting with Metadata Metadata describing data, resources, people, … needs to be flexible, expressive and dynamic. Metadata typically represented as a data model with attibutes and values. Main technology is RDF …

Resource Description Language (RDF) A model and syntax for metadata, that is a framework for describing and interchanging metadata Based on unique identifiers for both the things we describe (resources), and the ways we describe them (properties). In RDF, all things being described all called resources regardless of whether they're people, places, documents, movies, images, databases, etc. Identifiers are Uniform Resource Identifiers, or URIs (Uniform Resource Locator or URL is a type of URI) URLs for the location and retrieval of resources, URIs are unique identifiers for things that need not be retrievable.

RDF Based on statements in the form of triples: Object : attribute : value or here … Resource : Properties : Value Resource labeled by a URI Property labeled by a URI and can be a resource Value can be a string literal or a resource. Provides a graph-based data model.

RDF Graph: Example "there is a Person identified by http://www.w3.org/People/EM/contact#me, whose name is Eric Miller, whose email address is em@w3.org, and whose title is Dr."

RDF/XML http://www.w3.org/TR/rdf-primer/ <?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#"> <contact:Person rdf:about="http://www.w3.org/People/EM/contact#me"> <contact:fullName>Eric Miller</contact:fullName> <contact:mailbox rdf:resource="mailto:em@w3.org"/> <contact:personalTitle>Dr.</contact:personalTitle> </contact:Person> </rdf:RDF> http://www.w3.org/TR/rdf-primer/

Authoring RDF E.g. IsaViz: http://www.w3.org/TR/rdf-primer/

Ontologies Technologies for providing metadata, such as RDF still lack a “vocabulary” for understanding. Shared “ontologies” supply a common language that domains (applications and people) can use to understand the semantics of metadata. Ontology technologies include: RDF Schema or RDFS, OWL, DAML+OIL, …

Representing Ontologies Two main categories of schemes in the past: Frame-based/structured object based Protégé 2000, Ontolingua Intuitive modeling primitives and well used Logic-based (first order predicate logic) FaCT Well defined semantics and reasoning support.

RDF Schema (RDFS) W3C RDF vocabulary description language Too limiting for many applications

DAML+OIL Ontology language built for the web using XML and RDF Ontologies stored as XML and concepts referenced by URIs Adopted by many projects and has parsers and editors Describes a domain in terms of classes and properties Basis for W3C OWL ontology language

Examples Service discovery Knowledge annotation Workflow composition Data integration Collaborative science