W3C and the Semantic Web

2002-03-06

by Jos De Roo of AGFA

W3C Semantic Web Activity

• A key activity of the World Wide Web Consortium W3C (inventor T.Berners-Lee)
• W3C
  • develops interoperable technologies (specifications, guidelines, software and tools)
  • to lead the web to its full potential
  • as a forum for information, commerce, communication and collective understanding
• The semantic web
  • is an extension of the current one
  • focuses on the meaningful content of web pages
  • creates an environment where software agents roaming from page to page carry out sophisticated tasks for users
  • becomes a place where data can be shared and processed by automated tools as well as by people

W3C SW Activity - Goals

• Design of technologies that support machine facilitated global knowledge exchange.
• Making it cost-effective for people to record their knowledge.
• Focus on machine consumption

W3C SW Activity - Structure

• Part of the W3C Technology and Society Domain
• Working Groups for Enabling Standards and Technologies
  • The RDF Core Working Group
  • The Web Ontology Working Group
• Advanced Development
  • Explores pre-competitive, prototype development
• Education and Outreach
  • Clarifies design, goals, implementation guidelines
  • Position papers, Articles, Presentations, Tutorials, Tools

W3C SW Activity - Approach to Deployment

A lot of hard work - and a bit of luck

• Foster an environment for effective cooperation and collaboration
• Establish guiding architectural principles
• Facilitate the design of enabling standards and technologies
• Understand policy implications
• Focus on short term deployment
• Eye toward longer term research issues

SW Architecture

• Web
  • URI->Resource static mapping
  • Creates navigable "space"
  • Shared space = new genre of communication
  • Self-describing documents
  • URIs as identifiers not recipes
• Semantic
  • Machine processable
    • not natural language, human inference
  • For data: what you can do with it
  • For the future: conversion
  • Declarative

SW Principles 1: Everything identifiable is on SW

• All resources have identity
• People, places, and things in the physical world have online representations identified by URI's.
• URI's support participation, effective integration and are contextualized in SW.

SW Principles 2: Partial information is tolerated

• The current Web is unbounded.
  • Sacrifices link integrity for scalability.
• The Semantic Web it unbounded.
  • Anyone can say anything about anything.
• There will always be more to discover.

SW Principles 3: There is no need for absolute truth

• All statements on the Web occur in some context.
• Applications need this context in order to evaluate the trustworthiness of the statements.
• The machinery of the SW does not assert that all statements found on the Web are "true".
• Truth - or more pragmatically, trustworthiness - is evaluated by each application that processes the information on the Web.

SW Principles 4: Evolution is supported

• Allow effective combination of the independent work of diverse communities.
• Support the ability to add new information without insisting that the old be modified.
• Provide communities the ability to resolve ambiguities and clarify inconsistencies.
• Use descriptive conventions that can expand as human understanding expands.

SW Principles 5: Minimalist design

• Make the simple things simple, and the complex things possible.
• Enable simple applications now that plan for future complexity (eg. Dublin Core, RSS, MusicBrainz)
• Standardize no more than is necessary.
• Result more than the sum of the parts

Enabling Standards & Technologies - Layer Cake

RDF Core Working Group (RDFCore)

• RDF provides a common framework for representing metadata across many applications.
• Clarifies and improves RDF's abstract model and XML syntax according to implementor feedback.
• Completes the RDF vocabulary description in the RDF Schema Candidate Recommendation.
• Explains the relationships between the basic components of RDF (Model, Syntax, Schema) and the larger XML family of recommendations.
• Minimalist model - (thing), Class, Property
• Subproperty, Subclass
• Domain & Range
• Comments & labels

Very wide interoperability

Web Ontology Working Group (WebOnt)

• Standardize means for defining ontologies that can be used on the Web.
• Builds on RDF Schema (classes and subclasses, properties and subproperties)
• Extends these constructs to allow more complex relationships between entities (e.g.):
  • limit the properties of classes with respect to number and type
  • means to infer that items with various properties are members of a particular class
  • a well-defined model for property inheritance
• Input from the DAML+OIL work supported by DARPA's DAML Initiative
• More metainformation, such as
  • Transitive property
  • Unique, Unambiguous, Cardinality, etc
• Ontology community exists- DL, OIL, SHOE, etc. etc.
• Huge extra usage for extra functionality
• Not Turing complete

Wide interoperability & interconversion

Logic layer

• Universal language for monotonic logic
• Any rule system can export, generally cannot import
• No one standard engine - inference capabilities differ
• Many engines exist (SQL to KIF, Cycl, etc)
• Any system can validate proofs

SW Public Forums

• Semantic Web / RDF Interest Group
  • Dan Brickley mailto:danbri@w3.org (W3C/ILRT) chair
  • a forum for W3C Members and non-Members to discuss innovative applications of RDF and the Semantic Web.
• RDF Logic
  • detailed technical discussion of all approaches to the use of classical logic on the Web for the representation of data such as inference rules, ontologies, and complex schemata.
• RDF Calendar
  • public forum for discussion of RDF-based calendar and group scheduling systems
• Annotation and Collaboration
  • public forum for discussion of RDF-based annotation and collaboration systems

SW Advanced Development - Goals

• Explore pre-competitive, prototype ideas
• Venue for liaison with research community;
• Inform, be informed, nudge, be nudged
• Testbed for early implementations of Working Drafts
• Collaborative development environment for the Team and Members to explore ideas together
• Stimulate the development of more Semantic Web infrastructure components

SW Advanced Development - Areas

• Developer's Tools
• Resource Description
• Annotation, Collaboration, and Web of Trust
• Access Control Rules, Logic and Proof
• Calendaring and Scheduling
• Work-flow and Dependency Tracking
• Transformation and Extraction Utilities
• Integration with XML infrastructure

SW Bus

Examples of Running Code

Closed World Machine

• CWM is a popular Semantic Web & RDF program, written in Python by Tim Berners-Lee and Dan Connolly.
• CWM can handle the Notation3 format, as well as XML RDF and NTriples, and can perform a number of functions, including applying rules as a forward chaining inference engine.

Euler Proof Mechanism

• research component to support logic based proofs.
• Prolog unification (substitutions, unifiers) & resolution algorithm & backtracking
• Euler path detection
• "existential introduction rule" generation (w.r.t. RDF bNodes)
• unification of variable predicates
• use as much as possible from DanC's and TimBL's SWAP

Conclusions

• W3C Semantic Web efforts build common infrastructure
• First supports simple and then more complex systems
• Offers optimal reuse of data in networked environment
• More formal understanding of these relationships however are still required