Grid

This page describes a concept which is part of our glossary

A grid system is essentially a connector of resources involving two main aspects, resource abstraction and resource allocation.

The way that diverse resources can be connected in a grid system is by having a common interface to each type of resource (such as disk space or processing power). This interface involves both the API by which the system can physically interact with the resource (including all parameters about availability and performance etc), and a service level agreement which allows a price to be assigned to usage of the resource, and a cost to be assigned to delivery based on the level of performance. This arrangement creates an incentive driven system that minimises prices while maximising performance.

The resource allocation aspect can be thought of as a caching mechanism or "cashflow manager", but works over many different dimensions of resource rather than only the financial currencies. The general idea is to evolve an accurate report of the supply and demand across all resources in the system and how it changes over time.

The semantic web

The semantic web is an evolving extension of the Web in which web content can be expressed not only in natural language, but also in a form that can be understood, interpreted and used by software agents, thus permitting them to find, share and integrate information more easily. It derives from W3C director Tim Berners-Lee's vision of the Web as a universal medium for data, information, and knowledge exchange.

At its core, the semantic web comprises a philosophy, a set of design principles, collaborative working groups, and a variety of enabling technologies. Some elements of the semantic web are expressed as prospective future possibilities that have yet to be implemented or realized. Other elements of the semantic web are expressed in formal specifications. Some of these include RDF, a variety of data interchange formats (e.g RDF/XML, N3, Turtle, N-Triples), and notations such as RDFS and the OWL -- all of which are intended to formally describe concepts, terms, and relationships within a given knowledge domain.

RDF

Resource Description Framework (RDF) is a family of W3C specifications originally designed as a metadata model but which has come to be used as a general method of modeling information, through a variety of syntax formats.

The RDF metadata model is based upon the idea of making statements about resources in the form of subject-predicate-object expressions, called triples in RDF terminology. The subject denotes the resource, and the predicate denotes traits or aspects of the resource and expresses a relationship between the subject and the object. For example, one way to represent the notion "The sky has the color blue" in RDF is as a triple of specially formatted strings: a subject denoting "the sky", a predicate denoting "has the color", and an object denoting "blue".

This mechanism for describing resources is a major component in what is proposed by the W3C's Semantic Web activity: an evolutionary stage of the Web in which automated software can store, exchange, and use machine-readable information distributed throughout the web, in turn enabling users to deal with the information with greater efficiency and certainty. RDF's simple data model and ability to model disparate, abstract concepts has also led to its increasing use in knowledge management applications unrelated to Semantic Web activity.

• Getting into RDF & Semantic Web using N3

See also

• Web 3.0
• RDF
• Wikipedia:List of grid computing middleware distribution