1	Data and Meta Data on The Semantic Web
2	Topics Introduction to Semantic Web Semantic Web Architecture XML Resource Description Framework (RDF) Technologies and Applications
3	Remember When … Web was launched in early 1990s Exponential growth in mid-1990s Search engines took off as tool for finding resources Self-publishing increased amount of low quality hits from search engines Spammers attempt to fool search engines Difficulties in using the Web to find relevant resources
4	Definition "The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation." -- Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May 2001 The Semantic Web is the abstract representation of data on the World Wide Web (based on the RDF standards and other standards to be defined). (http://www.w3.org/2001/sw/)
5	Semantic Web Machines talking to machines – semantics need to be unambiguously declared Joined-up data – enabling complex tasks based on information from various sources Wide scope – from, say, home to government to commerce Trust – both in data and who is saying it This is not going to be easily achieved
6	The Evolving Web
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8	The Current Web Resources: identified by URI's untyped Links: href, src, ... limited, non-descriptive Humans: Characteristics of the documents is (normally) clear to those with a grasp of English. Machines: Very little structured information available for automated inference and/or delegation of tasks to an agent.
9	The Semantic Web Resources: Common naming syntax (URI's) Links: Common naming syntax (URI's) User: Richer user experience Machine: More processable information is available Computers and people: Work, learn and exchange knowledge effectively
10	Architecture and Enabling Standards & Technologies
11	Hypertext Markup Language HTML Enabled standard communication of content combined with format Loosely defined specific (limited) grammar specified using SGML (specific language) Started by Tim Berners-Lee Standardized by World-Wide Web Consortium (W3C) Ubiquitous method of presenting and communicating data Used throughout DoD on both public internet and SIPRNET and other classified networks Not useful for machine search
12	eXtensible Markup Language (XML) Separates content from format (standard syntax) Simplified version of SGML (metalanguage) for defining eXtensible tag sets Started by Tim Bray et al based on conversations with Tim Berners-Lee Standardized by W3C Used to define updated HTML grammar (XHTML) Used in Modeling and Simulation community primarily for Data Interchange Formats (DIFs) that support data sharing
13	“Perfect World” Behavior Sharing
14	XML Is Not Enough! XML: Should be used to add tags Is extensible (DC qualifiers) But: XML describes the syntax Does not provide semantics (what does DC.Creator mean?) The meaning may be agreed & understood within DC applications – but this does not allow for extensibility Similar applications may be described using different XML DTDs: e.g. is <Creator> the same as <le-Créator> or <Доклады>
15	Semantic Problems for XML Synonymy and polysemy <PERSON> vs. <INDIVIDUAL> is <SPIDER> an arachnid or software? Structural differences <PERSON><NAME>Lee Lacy</NAME><PERSON> vs. <PERSON><NAME> <FNAME>Lee</FNAME> <LNAME>Lacy</LNAME> </NAME></PERSON>
16	Resource Description Framework (RDF) RDF data consists of nodes and attached attribute/value pairs Nodes can be any web resources Attributes are named properties of nodes Values are either atomic (text strings, numbers, etc.) or other resources or metadata instances Supports labeled directed graphs XML used as graph serialization syntax for storing and communicating RDF instances Provides basic ontological primitives Classes and relations (properties) Class (and property) hierarchy RDF triples assert facts about resources
17	Basics of RDF Anything can be a resource. Resources have URIs. Resources have properties. Properties have values and types. An RDF document makes statements about resources and their properties.
18	A Simple Example “Jan Hanford created the J.S. Bach homepage.” The J.S. Bach homepage is a resource It has a URI (http://www.jsbach.org) It has a property The property has a type of “creator” The property has a value of “Jan Hanford”
19	RDF Graph
20	Translated to (simplified) RDF:
21	RDF Resource Description Framework An XML application “Not just tags” – RDF makes use of a formal model Basis for “The Semantic Web” (SW)
22	Namespaces added:
23	RDF based on ... AI (symbolic) Knowledge Representation Techniques – Semantic Networks and Frames Metadata Entity-Relationship (ER) - RDBMS Object-Oriented Modeling XML for file format URIs for identifiers Limited semantics (node-edge-node)
24	Why RDF Is Not Enough Expressive inadequacy Only range/domain constraints (on properties) No properties of properties (unique, transitive, inverse etc.) No equivalence, disjointness, coverings etc. No necessary and sufficient conditions (for class membership) Poorly (un) defined semantics
25	Semantic Web (SW) Provides agent-readable descriptions of data, information, and knowledge Built on top of XML and RDF Envisioned by Tim Berners-Lee and researched by DARPA team and others W3C is beginning a Semantic Web initiative Used to define ontologies and associated instance data Huge potential for Modeling and Simulation community
26	Ontology layer More meta-information, such as Properties of each relation (transitive, inverse, symmetric, etc.) Taxonomic hierarchies Uniqueness constraints, Cardinality, etc. Ontology community exists- OWL, etc.
27	What is an Ontology?
28	DAML+OIL Developed by DARPA team of researchers Language based on description logic technology Starting point for W3C semantic web initiative (OWL is replacing DAML) Adds additional language features for describing ontologies Builds on RDF(S)
29	Fugitive / Terrorist Description Ontology Based on FBI website information Potential applications for “watch list” matching Description properties include: Place of birth FBI caution Physical description Languages spoken
30	Commercial Ship Ontology
31	Joining Ontologies
32	Proof and Logic Layers Inference rules Query Languages Evolution rules Universal language for monotonic logic Some engines exist (SQL to KIF, Cycl, etc)
33	Web of Trust 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 Semantic Web does not assert that all statements found on the Web are "true".
34	Applications Ontologies Catalogs on the Web Electronic commerce transactions Operating across many applications (e.g., PDAs) Intelligent Agents ?
35	Working Examples Resources http://www.eece.memphis.edu/ksl/ks1/hail001.xml http://www.eece.memphis.edu/ksl/ks1/sebring9210.xml http://www.eece.memphis.edu/ksl/ks1/engine001.xml http://www.eece.memphis.edu/ksl/ks1/sebring9210damage01.xml http://www.eece.memphis.edu/ksl/ks1/lili.xml Ontology http://www.eece.memphis.edu/ksl/uofm_eece.xml
36	Semantic Web Conclusions The first version of the Web lacked a metadata framework which was needed to describe resources W3C developed RDF to provide this framework The Semantic Web will be based on registries of machine-understandable definitions The Semantic Web will be difficult to achieve Applications are needed to show the utility of the Semantic Web infrastructure currently being developed.