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Semantic Grid

Ferenc Vajda

vajda@sztaki.hu

Computer and Automation Research Institute

Hungarian Academy of Sciences

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Data/Information/Knowledge

Data: observed facts

Information: organized and related facts with attributed properties

Knowledge: “sum of what is known”: concepts, objects with characteristics, principles, laws, know-how, etc.

Semantics: a term used for meaning, interpretation, knowledge through reasoning

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Different Evaluations of the Grid

1. Grid generations

• To link supercomputer centers

(e.g. I-way)

• Toolkit- and middleware-based

(e.g. Globus)

• Service-oriented (OGSA)

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Different Evaluations of the Grid 2.

2. Based on the technologies used

• Protocol-based

• Service-based

• Semantic Web based

3.Based on application requirements

• Data/computational Grid

• Information Grid

• Knowledge Grid

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Problems Related to Semantic Web

• Knowledge Evaluation

• Knowledge Representation

• Ontologies

• Agents

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Resource Description Framework (RDF)

-Set of triplets: subject, property,object

• Metadata: structured data about data

• Resource identification: Universal Resource Identifier (URI)

• Most common type of URI: Uniform Resource Locator (URL)

• Qualified URI: URI + fragment identifier

• Concepts:

-Graph model

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RDF 2.

Subject ObjectProperty

-Data types: based on XML Schema

-Vocabulary: URI-based (Both nodes and arcs)

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RDF 3.

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What is an Ontology?

Greek: ontos = being, logos = science

• world view regarding a domain

• shared understanding

• definitions, inter-relationship

• conceptualization

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What does an Ontology look like?

• vocabulary of terms

• specification of their meaning (i.e. definitions)

- highly informal (natural language)

- semi-informal (restricted, structured form of natural language)

- semi-formal (artificial, formally defined language)

- rigorously formal (formal semantics, proofs, completeness)

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Use of Ontologies

• communication (between people and organizations)

• system engineering (specifications, reusable components)

• inter-operability (between systems)

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Ontologies

• Web Ontology Language (OWL)

• Ontology: defines the terms used to describe and represent an area of knowledge

-taxonomy: object classification + relationship among them (properties and inheritance of properties)

-inference rules

• DAML (DARPA = Defense Advanced Project Agency

Agent Markup Language)

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Agents

Agent: Capability to understand and integrate diverse information resources (based on domain ontologies)

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Agents 2.

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Semantic Web Layers

Credit to Berners-Lee (XML2000 address)

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Semantic Grid

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Semantic Grid

Basis:

• Metadata enabled

Goal:

Grid + Semantic Web

• Ontologically principled

New e-Science infrastructure

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Services

e.g. -semantic database integration

-semantic workflow description

• Base services

-data/computational services (network access, resource allocation and scheduling, data shipping, etc.)

-information services (queryprocessing, event notification, instrumentation management,

etc.)

• Semantic services

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Services 2.

-application

• Knowledge services

-acquisition

-modeling

-publishing, use and maintenance

-resource management

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Knowledge Grid Architecture

Credit to Carole Goble et al.

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Roles of Ontologies

Credit to Carole Goble et al.

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The term ‘procedure’ used by one tool is translated into the term ‘method ‘ used by the other via the ontology, whose term for the same underlying concept is ‘process’. procedure

viewer

translator

Ontology

method

library

give me the procedure for…

translator

here is the

METHOD for…

procedure = ???

procedure =

process

give me the

process for…

here is

the process for…METHOD =

process

??? = process

Roles of Ontologies (Example)

Credit to Rokhlenko Oleg

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Knowledge Services

Credit to Carole Goble et al.

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Typical Applications

• Service discovery

• Knowledge annotation

• Workflow composition

• Data interpretation

• Collaborative science

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Grid Service Discovery

Simple discovery

• attribute-base

• name lookup

• type matching

Semantic discovery

• matchmaking

• based on ontology description

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Brokering vs. Matchmaking

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Grid Service Discovery Framework

Ontology based description used by• service provider

• service requester

• service matchmaker

• service registry database

Matchmaking process

• comparison: request to registry

• decision: based on filters

• information

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Service Description

“What the service does”: service profile

“How it works”: ServiceModel

“How it is used”: ServiceGrounding

Description by RDF(S): Resource Description Framework Schema

Service profile

• description (human readable)

• functionalities

• functional attributes

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Service Description 2.

Credit to DAML-S White Paper

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Filtering

Independent filtering is based on

• context matching

• syntactic matching

- comparison of profiles

- similarity matching

- signature matching

• semantic matching

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myGrid project

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Role of Ontologies in myGrid