1	Digital Libraries The Semantic Web: Making sense of it all Week 6 Min-Yen KAN
2	Motivation for semantic web “The primary goal is to make the web more like a library and less like a heap of messy books on the floor.” -Tim Bray, Textwise consultant The Web can reach its full potential only if it becomes a place where data can be shared and processed by automated tools as well as by people. - Semantic Web Activity Statement
3	So, what is it anyways? An extension of current the web that allows: Exchange of data By software agents Will allow agents to reason Needs to be able to seamlessly exchange data
4	Other examples: Services off the desktop
5	Or perhaps on different desktops…
6	This is great, why didn’t we think of it sooner?!? As a community, we have been trying: Doug Lenat spun off a company to try to capture commonsense knowledge in a huge knowledge representation project. 1,000,000 assertions captured. Cyc knows that trees are usually outdoors, that once people die they stop buying things, and that glasses of liquid should be carried right-side-up. What’s different about the Semantic Web?
7	CYC and the Semantic Web One company Centralized First-order logic Complex KR language Authoritative data Many companies Distributed Left up to agent Simple KR language Noisy data
8	Implementing SW For the semantic web to function, computers must have access to: structured collections of information and sets of inference rules that they can use to conduct automated reasoning. Adding logic to the Web — the means to use rules to make inferences Uses XML and RDF as a framework
9	Semantic Web problem Islands of XML from disparate web services Example : Tori Amos Up to consumer to put these chunks together Situation analogous to pre-web hypertext systems and RDBMS today
10	Semantic Web problem
11	TAP Goal Create a coherent semantic web from disparate chunks Effectively make the web a giant distributed DB Why --- Bringing the Internet to programs
12	SW Layer Cake
13	Resource Description Framework Encodes knowledge in sets of triples A document makes assertions that: particular things (people, Web pages or whatever) have properties (such as "is a sister of," "is the author of") with certain values (another person, another Web page).
14	RDF Model A model for representing named properties and property values models the equivalence relation Simply a triple of the form:
15	RDF / XML: assertion interchange Simplified XML Syntax for RDF Encodes RDF as machine parsable XML Verbose, not really readable by humans Note: counter to what one of XML’s primary motivations. RDF and XML are complementary: XML only gives structure (validating with a DTD) RDF adds to XML the ability to encode simple propositions
16	RDF Schema – Basis for ontology RDF with XML: encode assertions Still need to be able to exchange and reason on the data To build the necessary ontology, RDF Schema was designed to be a simple data typing model for RDF
17	RDF Schema Core classes,properties,constraints rdfs:Resource rdfs:Property rdfs:Class rdf:Type rdfs:subClassOf rdfs:PropertyOf rdfs:ConstraintResource rdfs:ConstraintProperty rdfs:range rdfs:domain
18	RDF Schemas The first three most important concepts in RDF datatyping schema: Resource (rdfs:Resource) are objects that are uniquely identified by an URI Note: URI not URL. Question: What is a URI? Property (rdf:Property) express the relationships of values associated with resources Class (rdfs:Class) are resources denoting a set of resources
19	RDF schema example Book rdf:type rdfs:Class . :bookTitle rdf:type rdf:Property . :bookTitle rdfs:domain :Book . :bookTitle rdfs:range rdfs:Literal . :MyBook rdf:type :Book . :MyBook :bookTitle “My Book” There’s a type of resource called “Book” There a type of property called “BookTitle” “BookTitle”s are a property of “Book”s … and they can take a literal string value MyBook is a type of Book MyBook’s title is “My Book”
20	What about incompatible schemas? SW’s Answer: OWL RDF Schema is fine if one person/organization is authoring all of SW Inconsistencies among different authors OWL strengthens RDF Schema with some 30 additional interchange properties
21	References SW ontology development information (DAML): http://derpi.tuwien.ac.at/~andrei/daml.htm Introduction to RDF Schema http://www.dlib.org/dlib/may98/miller/05miller.html RDF and RDF schema www.wastl.net/download/slides/rdf_overview.pdf OWL http://www.w3.org/TR/owl-ref/
22	To think about… What are XML namespaces and how do they figure into the RDF syntax? Minimalist architecture makes the web scalable, will it make the SW workable? SW is not (yet fully) standardized Help everyone out and see what you can contribute! What’s your prediction when the SW will “arrive”?