motivation
	- XML is allready accepted as the standard for data
	  interchange on the web
	- example
	- XML is good to represent structured data but for
	  the machine it does not express meaning
introduction
	Resource Description Framework
	- general purpose language for representing information
	  in the World Wide Web
	- intended to represent metadata about web resources
	- can be used to represent information about everything
	  (generalisation of the concept "web resource")
	Information Exchange
	- framework for expressing information in way that it can
	  exchanged between applications _without_ loss of meaning
	- information may be available to other applications than
	  those for wich it was originaly created.
	Example
	- XML syntax example
	- natural language explanation
	- machine readable / XML based syntax
	- links data across web (and not across web)
	Complete Specification consists of severl documents
	- RDF Model Theory
	- RDF/XML syntax
	- RDF Schema
	- RDF Test Cases
	- RDF Primer
	- ... even more http://w3.org/RDF/
	                http://w3.org/TR/
	Scope of this presentation
	- what information can RDF represent?
	- what does RDF look like?
	- how is RDF information created, accessed and processed?
	- what are the known RDF applications ?
	- more about RDF model theory
making statements about resources
	The Nature of RDF
	- making statements about resources
	- example (in natural english )
	- to formulate this kind of statements we need:
	  - a way to identify the thing we want to describe (subject)
	  - a way to identify the property
	  - a way to identify the vlue (object)
	= s p o notion + url for web resources
	- of course we want to do this machine readable, we need
	  - system of unique machine processable identifiers
	  - machine processable format for representing these statments and
	    exchanging them between machines
	URIs
	XML
	  - example
	  - the use of Namespaces
	  - RDF defines a specific XML markup language to use in writing down
	    RDF information
	The RDF Model
	Structured Property Values
	- blank nodes
	
xml synrax for RDF
	examples
defining RDF vocabularies: RDF schema
        RDF Schema
	- RDF defines simple data model for describing proerties or resouces
	- RDF user communities need to have mechanisms to define such terms
	- RDF does not provide mechanisms to define terms like propertie
	  and classes
	- for definig such term one constructs RDF Schema.
	- RDF Schemas are defined in RDF Schema Specifications
	- RDF Schema provides mechanisms to define classes, properties and
	  control how classes and properties are used together
	- we call such RDFS documents vocabularies
	Type System
	- similarity with OO design
	- RDFS provides basic type system for use in RDF models
	- this allow resources to be defined as instace of one or more classes
	- classes to be organized hierarchicaly
	RDFS vocabulary
	- RDFS uses the RDF data model itself to define the RDF type system
	- RDFS Specification provides set of predefined RDF resources and
	  properties that can be used to define user-specific classes and
	  properties - the RDFS vocabulary
	- the RDFS vocabulary
	Classes
	- all things described in RDF are called ressources and are considered
	  to be instances of tpe predefined class rdfs:Resource
	- rdfs:Resource is the topmost class in the hierarchy
	- rdf:type property is used to indicate that a resource is an instance
	  of a class (object is allways a resource which is a class)
	- class is a resource having rdf:type property with value rdfs:Class,
	  which is a predefied resource
	- example
	- rdfs:Class is itself a class (an instance of rdfs:Class) :))
	- one resource can be an instance of multiple classes
	- predefined rdfs:subClassOf property represents trasitive 
	  subset/superset relation on classes. (inherritace)
	Properties
	- rdfs:Property
	- rdfs:subPropertyOf
	- rdfs:domain
	- rdfs:range
	Upside Down OO design notion
	- properties defined with constrains for classes
	- this allow prperties to be more reusable in resources definitions
	- propertes may be used in situations not intendeb by the origial
	  definer
	- RDF Schema specification does not say how should applications deal
	  the constrains
RDF containers
	Why containers
	What containers
	- Bag
	- Sequence
	- Alternative
some RDF applications
	Dublin Core Meta Data Initiative
	PRISM (Publishing Requirements for Industry Standard Metadata)
	OWL
	OIL
RDF model theory
	Basics
	- hierarchic network analogy
	- graph represetaion
	- subgraphs
	- interpretations
	Monotonic Reasoning
	- each triple make a distinct assertion
	- meanining of ay triple if not changed by adding other triples
	- cannot express: CWA, local default preferences, other common
	  nonmonotonic constructs
	Direct Translations Fail on FOL
	- uniref --> logical constant
	- literal --> quoted string
	- arc s p o --> p(s,o)
	- RDF graph --> existential closure of conjunction of translations
	  of all arcs
	- as properties are orinary resources we can same symbol as an object
	  and as an predicate :(