Introduction to Resource Description Framework
- RDF
The
Resource Description Framework otherwise shortly called the RDF is a framework
or an infrastructure that is used for exchange of metadata. This framework
is also used for encoding and reusing the structured metadata. Resource
Description Framework uses XML for imposing the restrictions to enable
to follow a structured representation of data so that the data can be
exchanged, encoded and reused.
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The Resource
Description Framework describes the resources available in the internet.
RDF has a model to describe these resources. A resource can be said to
be anything that is identified by a Uniform Resource Identifier (URI).
Resources have properties and properties have values. The values of the
properties can be as simple as a text or a string or it can be another
resource. A description is a collection of such properties that points
to the same resource. The Resource Description Framework has the characteristics
such as independence, interchange, scalability, properties, values, and
a combination of properties and values that can be said to be statements.
RDF is said
to have a characteristic called independence since anybody in the world
can create a resource that can be referred by anyone. Since a resource
is a URI in the web and that can be created by any person it is said that
RDF is independent. The other characteristic of RDF is interchange. The
RDF statements if converted to XML can be easily interchanged with other
resources. Hence the characteristic interchange. Since any number of resources
can be created in the web it is scalable.
The relationship
between resources, properties, and values can be best understood when
we consider an example for RDF. Consider a person “Peter” who
is the “Editor” of a “Magazine”. In this case you
can consider the “Magazine” as a Resource and “Editor”
as the Property and “Peter as the value of the property Editor. If
the person Peter is an employee of some company say “XYZ” and
that too has to be represented in this RDF model, the value of the resource
can point to some other resource which will give information regarding
the person Peter. That resource may give information regarding the company
of the person and other information about the person. These relationships
can be best understood if given in the form of a flow diagram which gives
the relationships.
Though the
above hierarchical relationships can be best understood by the humans
if given in the form of flow diagrams, the machine and the programs cannot
understand that form of representation. Hence there is a need for syntax
for representing that information so that other applications can understand
the information represented and enables the applications to exchange that
data with other applications. Hence there is a need for RDF syntax to
represent data. This can be best understood with a simple example given
below:
<?xml:namespace
ns = "http://www.w3.org/RDF/RDF/" prefix ="RDF"?>
<?xml:namespace ns = "http://somenamespace" prefix = "ME"?>
<RDF:RDF>
<RDF:Description RDF:HREF = "http://uri-of-Magazine">
<ME:Editor>Peter</ME:Editor>
</RDF:Description>
</RDF:RDF>
In the above
code, the element <RDF:RDF> and </RDF:RDF> is just a wrapper
for the XML document as is the case for all the XML documents. The namespace
for RDF is given in the first statement of the XML document. Any other
elements which have a unique namespace are also given in the document
as in the second line of the XML document given above. The element <RDF:Description>
is used to initiate the URI of the resource as “http://uri-of-Magazine”.
The element <ME:Editor> is used to represent the property of the
Resource in the context of the <RDF:Description>. This property
has a value of “Peter”. The example given above is a simple
example in which the relationship of the Resource, Property, and Value
are given and the code gives how these are represented in a RDF document.
Consider
a case where a Property should refer to another Resource which would give
more details about the concerned Resource. The example given below explains
this scenario.
<?xml:namespace
ns = "http://www.w3.org/RDF/RDF/" prefix="RDF" ?>
<?xml:namespace ns = "http://somenamespace " prefix="ME"
?>
<?xml:namespace ns = "http://someothernamespace " prefix="Company"
?>
<RDF:RDF>
<RDF:Description RDF:HREF = "http://uri-of-Magazine ">
<ME:Editor RDF:HREF = "#Edit_Mag"/>
</RDF:Description>
<RDF:Description
ID="Edit_Mag">
<Company:Name>Peter</Company:Name>
<Company:Email>peter@mag.net</Company:Email>
<Company:Address>Mag, Inc.</Company:Address>
</RDF:Description>
</RDF:RDF>
The element
<ME:Editor> which gave a value in the previous example now refers
to another resource with ID as Edit_Mag. This resource gives more information
about the editor such as his name, the email address and the company address.
By following these syntax RDF helps in exchanging information about information.
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