Motivation Resource Description Framework (RDF) Describe all - - PowerPoint PPT Presentation
Motivation Resource Description Framework (RDF) Describe all resources Make them machine-readable Provide common framework among different applications How to do this? What is RDF? Create a framework using an application-
Resource Description Framework (RDF) Motivation
Describe all resources Make them machine-readable Provide common framework among different
applications
How to do this?
Create a framework using an application-
independent syntax: XML
What is RDF?
Describes attributes about objects Can point to other objects described by RDF Creates a graph of resources Resources are identified by URIs
What is a URI?
Universal Resource Indicator Consists of prefix and description URL is a type of URI
Resource Description Framework (RDF)
RDF/XML Syntax
RDF/XML
RDF/XML is valid XML It uses a standardized set of tags to
represent an RDF graph
The RDF graph has node-arc-node triples
that represent subject-predicate-object relationships
RDF/XML
The relationships are represented by nested
XML tags
Following the nesting of the tags is
equivalent to traversing the graph
<rdf:Description> is the tag used to begin a
node
RDF/XML
The tags use URI as attributes to identify
what they describe
In the case of an arc or predicate the URI is
appended with a local reference
The URI can then be replaced with a
namespace to shorten the tag length
RDF/XML
<?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ex="http://example.org/stuff/1.0/"> <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar" dc:title="RDF/XML Syntax Specification (Revised)"> <ex:editor> <rdf:Description ex:fullName="Dave Beckett"> <ex:homePage rdf:resource="http://purl.org/net/dajobe/" /> </rdf:Description> </ex:editor> </rdf:Description> </rdf:RDF>
RDF
A language for representing information
about resources in the World Wide Web.
Based on XML syntax. Used to describe the title, author ect for
webpage.
The concept of a ‘web resource.’
RDF
RDF is intended for situations where information
needs to be processed by applications, rather then being only displayed to people
RDF is based on the idea of identifying things that
use Web identifiers (URI)
Describes things in simple terms of properties and
property values.
The resources of RDF are not fixed
Basic Concepts of RDF
Subject-The resource we are talking about Predicate-A property of that resource that we
wish to describe
Object-The value of the predicate. The
predicate
In Plain English
http://www.example.org/index.html has a
creator whose value is John Smith
RDF
RDF is designed so machines can identify
resources.
Querying RDF is based on the concept of a
URI
Uses XML to describe all its information
Graph Representation
Graph Representation
There can be a larger graph where there are
multiple predicate/object tuples defining an
Graph Representation Tuples
Or data can be defined in tuples: <http://www.example.org/index.html>
<http://purl.org/dc/elements/1.1/creator> <http://www.example.org/staffid/85740> .<http://www.example.org/index.html> <http://www.example.org/terms/creation-date> "August 16, 1999" .<http://www.example.org/index.html> <http://purl.org/dc/elements/1.1/language> "en" .
RDF
Each triple corresponds to a single arc in the graph
above
RDF does not associate meaning any more then a
database associates meaning to its table names and
and a querying method.
When data needs to be more structured it can be
broken up into pieces for instance with an address
RDF Blank Nodes
Blank nodes are used to represent a more accurate
description of a model. For instance john and johns address are not the same object and therefore there should be arcs that separate them from each other.
In the triples notation URI objects must be enclosed
in angle brackets.
RDF uses blank nodes to represent n-ary
5 way relationship.
Types Types
All of the previous objects have had no type.
However in the example above the author most likely intends to mean 27 interpreted as a number.
In RDF we define an objects type by pairing it
with a type definintion. For example with integers this is xsd:integer.
The xsd is shorthand for a descriptor of its
type.
Types
We can write this in the triples representation
as follows:
ex:index.html exterms:creation-date "1999-
08-16"^^xsd:date .
RDF has no built in datatypes of its own.
Similar to soap however the user can describe any object datatype by associating a type to it.
Types
Technically the type associations have no
actual meaning since the RDF document
does not enforce it. The type is only used to describe the intended meaning of an object.
Resource Description Framework (RDF)
Applications
Applications
RDF is used for storing metadata We use metadata all the time
Searching the library Looking up a phone number in the Yellow Pages
It is possible to perform them without metadata
Search the books one by one Dial every possible phone number until you get the right one
These searches are made easy because of
metadata
How Does RDF Make Life Easier?
RDF can be used for:
– Search engines – Web Services – Internal relationships between items – Web Mining – Standardized metadata access
– Industry standards – Searches – Storage – Interoperability
RDF and Search Engines
Currently search engines operate on a “brute force” discovery
method
RDF allows for an efficient, structured and organized way to
search for information
Search engines like Vivisimo will become more ubiquitous
because RDF allows for an efficient querying of metadata
– Higher precision in resource discovery than with full text
search engines
The aim: to provide a uniform query capability for
resource discovery
Possible because of the way RDF can structure and
programs
RDF and Web Services
RDF provides a structured way to describe both the semantics
and syntax of your web service.
As seen with the project, organizing and finding out what the
format and syntax of a web service call is a somewhat arduous process
With RDF, this discovery process could be made much easier
and much more seamless
RDF and Web Mining
RDF can enhance web mining With a standardized way to represent
metadata, the process of extracting patterns and “massaging” this data becomes much easier
Less resource intensive
RDF and Multimedia Databases
Currently most multimedia databases either rely on
text searches of captions of an image or on properties of the actual content of the file
Image – global color histogram, layout Audio – length, frequency signature
Metadata about multimedia files can be created with
RDF and this can provide a much more powerful way for searching through multimedia databases
The problem: While this metadata is great for
searching, who is going to input this metadata?
Automated metadata generators are far from perfect
information about the picture
be efficiently and conveniently searched
RDF – An Example RDF Examples Some examples of where RDF can be used.
Describing properties for shopping items, like price
and availability
Describing time schedules for web events Describing information about web pages, like
created and modified date, title, and author
Describing content and rating for web pictures Describing content for search engines Describing electronic libraries
An example which omits Namespaces.
<?xml version="1.0"?> <RDF> <Description about="http://www.w3schools.com/default.asp"> <author>Jan Egil Refsnes</author> <created>November 1, 1999</created> <modified>February 1, 2004</modified> </Description> </RDF>
Resources, Properties, and Values / Subjects, Predicates, and Objects
The previous example analyzed. http://www.w3schools.com/default.asp is the
resource or subject
The element <author> is a property or predicate The value "Jan Egil Refsnes" is a value or object.
A more detailed example.
<?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:bug="http://www.microsoft.com/bugs"> <rdf:Description rdf:about="http://www.microsoft.com/bugs/Windows/"> <bug:name>Program Not Responding</bug:name> <bug:severity>FATAL</bug:severity> <bug:program>Internet Explorer</bug:program> <bug:errorcode>0x28FA28FA28F2FF...F8FAF83FFE38FE38F</bug:errorcode> <bug:time>12:31:43 PM</bug:time> </rdf:Description> ... </rdf:RDF>
Analyzing Again...n...again....zzzzzzz
that the content is RDF.
namespace defined by "http://www.w3.org/1999/02/22-rdf-syntax-ns#".
namespace defined by "http://www.microsoft.com/bugs".
/rdf:Description) contains the description of a resource identified by the rdf:about attribute.
bug:severity, etc.
WAKE UP!!!!!!......this is funny...
<?xml version="1.0"?> <rdf:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xml:base= "http://www.animals.fake/animals"> <rdf:Description rdf:ID="animal"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> </rdf:Description> <rdf:Description rdf:ID="horse"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> <rdfs:subClassOf rdf:resource="#animal"/> </rdf:Description> </rdf:RDF>
Whats the diff?? It all looks the same...
RDF Schema does not provide actual application-specific
classes and properties.
Instead RDF Schema provides the framework to describe
application-specific classes and properties
Classes in RDF Schema is much like classes in object oriented
programming languages. This allows resources to be defined as instances of classes, and subclasses of classes.
Note: in the previous example horse and dog are subclasses of
animal.
Any Questions?
...and they lived happily ever after.