Semantic Web

This talks summarizes material from

Tim Berners-Lee, James Hendler, and Ora Lasilla. The Semantic Web. [1] Scientific American, 2001.
James Hendler. Agents and the Semantic Web. [2] IEEE Intelligent Systems, (16)2. 2001.

1 The Vision

Most of the current web content is designed for human consumption.
The semantic web will change that by:
- Adding semantic tags, the meaning of these tags will be given by ontologies
- The ontologies will also provide inference rules.
- The whole thing will be as decentralized as possible. No central ontology. No central reasoning engine or rules.
It will (has?) lead to the development of Internet-based multiagent systems that share-search-buy-sell information on behalf of the users.
Check out Tim's video [3] and also this one [4].

2 Knowledge Representation

Traditional AI methods have been centralized: one ontology, one set of inference rules, one program. They work!
SW accepts that paradoxes and unanswerable questions are the price to pay for versatility. SW is to KR as the web is to a database system.
SW focuses on openness and interoperability above all else (e.g., functionality).
As such, it champions XML as the syntax and the Resource Description Framework (RDF) as the semantic language.
RDF is "logically simple". It encodes meaning in triples: subject, verb, and object.

3 Semantic Links

4 Graphs

RDF can be viewed as a graph where the nodes are the subject or objects and the links are the verbs.
Various RDF graphs can be superimposed on each other, leading to new meaning.

5 Semantic Web Architecture

6 Ontology Layer

Encodes meta-information, such as
- Transitive property
- Unique, Unambiguous, Cardinality, etc
RDF will probably be the standard lower-level encoding.
OWL will probably be the ontology language.
The actual ontologies are yet to be determined.

7 Ontology Creation

Many ontologies, all pointing to each other.
But, we need users to mark up their web pages:
- Have the "save as html" feature add semantic markup.
- Web pages generated by content-aware products (e.g., "Personal Web Page Maker", "Instant Retail Website", "eFanSite ©").
Ontologies will be created incrementally.
- A pet store owner could select to use a biological taxonomy ontology and a commercial one, and add a descriptor field to animal called product shipping type.
- He can also create new subclasses and publish this new ontology.

8 Ontologies, Agents, and Services

Web services are the backbone of the SW, as well as the .NET and ONE initiatives.
The SW will create machine-readable ontologies that describe services.
These descriptions will be used by "capable" agents. They will be able to find matches up and down the class hierarchy and follow other type of semantic links.
A machine-readable description of the service and logic describing the consequences of its use can also be included.
We could also use DAML+OIL to define an ontology of the terms needed to describe the invocation of services. This could be done by describing them as FSMs.

9 Service Class

10 Agents and Ontologies

Big boxes are ontologies, small boxes are agents.
Agents can use the same or related ontologies. This would allow for some degree of functionality.

11 Logic Layer

12 Semantic Web Bus

13 Deployment

14 Knowledge Evolution

The SW can assist the evolution of human knowledge as a whole.
Coordinating actions across a large group is painfully slow and takes an enormous amount of communication.
The SW names every concept by an URI. It lets anyone express new concepts that they invent with minimal effort.
This will make human knowledge and its workings available to agents.
Knowledge Revolution!

15 Semantic Web is Happening Now

[5]

1 The Vision