Transcript RDF Resource Description Framework

By: Dan Johnson & Jena Block
RDF definition
What is Semantic web?
Search Engine Example
What is RDF?
Triples
Vocabularies
RDF/XML
Why RDF?
A standard for encoding metadata and
other information on the Semantic
Web
•A project that aims to enable machines to do the searching,
aggregating and combining of the Web's information without a
human operator
•An extension to the Web that adds new data and metadata to
existing Web documents, extending those documents into data
•An abstract intention to apply machine-exclusive meaning to
the information on the web
• Documents that are not “Semantic” are in a language
specific to people
• To make these documents “Semantic” we must apply a
framework to the data within the document so the
computer can understand it
Search:
“Tapioca Pudding”
Blah blah blah blah
tapioca blah blah
blah pudding.
Chocolate pudding,
blah blah blah
tapioca shake. Blah
blah blah blah. Blah
blah blah blah
tapioca pudding.
Semantic Search Engine
Search for:
“Restaurants that
serve Tapioca
Pudding”
Search
Restaurants
Menus
Desserts
Sides
Search for:
“Recipes for
Tapioca
Pudding”
Search
Recipe Sites
Desserts
Sides
Semantic search is narrower,
more specific, and more
efficient
•Resource Description Framework
•Enables the encoding, exchange and reuse of structured
metadata
•A general method to break down data into smaller pieces
with rules of the semantics of those pieces
•A way of putting web data into a context which the
computer can understand
We already have ways of putting web data into a
context which the computer can understand
• Databases use tables
• XML uses hierarchies
However, these techniques can be too restrictive
The data below is too flexible to be represented by a table or
hierarchy so we use a graph
To describe the data in the graph in terms that the computer can understand,
we describe each relationship individually
e.g. “vincent_donofrio” “starred_in” “the_thirteenth_floor”
•RDF is a method used to break down knowledge
into smaller pieces called triples
•Gives rules about the semantics to these pieces
•Subject, predicate, object – the subject and the
object are two things in the world and the
predicate is the relation between the two
Subject
Object
Predicate
my_house
has_a
couch
Using triple format, we can describe any series of relationships
in a way that the computer can understand
e.g. “The quick brown fox jumped over the lazy dog”
Subject
Predicate
Object
Fox
is_the_speed
Quick
Fox
is_the_color
Brown
Dog
is_just
Lazy
Fox
jumped_over
Dog
Although we’ve described the relationships in the sentence, the
computer still doesn’t know what these words or phrases
actually mean, to solve this problem we must make a vocabulary
•Vocabulary (n) – a list of words and phrases of a language
•When we create an RDF file we need to define the terms we use
•We do this using a vocabulary built for the computer
Term
Dog
Fox
Quick
Brown
lazy
is_the_speed
is_the_color
is_just
jumped_over
Definition
an object
an object
a speed
a color
an attribute
gives a speed to an object
gives a color to an object
gives an attribute to an object
gives the action/position relationship between two objects as
one jumping over the other
We can use vocabularies that we build or we can use existing
vocabularies published by someone else
Dublin Core
Property
Definition
Contributor An entity responsible for making
contributions to the content of the
resource
Coverage
The extent or scope of the content of
the resource
Creator
An entity primarily responsible for
making the content of the resource
Format
The physical or digital manifestation of
the resource
Date
A date of an event in the lifecycle of the
resource
Description
An account of the content of the
resource
The W3C specifications define an XML format to encode RDF
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:fd="http://www.fox_and_dog.org/">
<rdf:Description rdf:about=fd:Fox>
<fd:is_the_speed>"quick"</fd:is_the_speed>
<fd:is_the_color>"brown"</fd:is_the_color>
<fd:jumped_over rdf:resource=fd:Dog/>
</rdf:Description>
<rdf:Description rdf:about=fd:Dog>
<fd:is_just>lazy</fd:is_just>
</rdf:Description>
</rdf:RDF>
The RDF/XML format has the following rules:
• Root element must be <RDF>
• Vocabularies are referenced using XML namespace
• The RDF triples are organized using the
<Description> tag
•
•
•
The subject is named in the about attribute
The child nodes within the <Description> tag are the
predicates
Their content is the object
“Dog” “is_just” “Lazy”
<rdf:Description rdf:about=fd:Dog>
<fd:is_just>lazy</fd:is_just>
</rdf:Description>
•RDF/XML is only one of many types of notation
for RDF and is the only one that utilizes XML and
XML namespace
•The major difference between to two is in the
data model
• XML is hierarchical
• RDF is relational
•Allows multiple users the freedom of their own
format while maintaining interoperability
•RDF can be as descriptive as the English language
while maintaining an organization that the
computer can understand
However,
the question of how an application will
retrieve these files has not yet been answered
http://www.rdfabout.com
http://www.w3.org/RDF/FAQ