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GeoRSS in RDF

RDF: a quick introduction

This material is preliminary and only for discussion at this time.

The RDF data model is so simple that it can be explained in a few paragraphs.

RDF encodes information using statements of the form
"the object O has property P with value V". The value of a property may be a literal value,
such as a string or number, or another object. Properties and objects are usually named using URIs.
Here is an example:

    the Object http://en.wikipedia.org/wiki/Astoria_Oregon has 
    the Property http://www.georss.org/georss/point with value
    "46.183 -123.816".

This statement means that the geographical location associated
with the specified Wikipedia page has latitude 46.183 and longitude
-123.816. In this case, the object is a web page, but physical or conceptual
entities can also be named by URI in RDF statements.

A unit of RDF content (eg an RDF page) is nothing more than a set of such statements.
If the objects and literals are construed as nodes, and the statements as edges,
the RDF data model can be viewed as a labeled directed graph. In particular, the statement
"A has property P with value B" is represented by an edge labeled P joining node
A to node B.
The detailed rules concerning labeling are: an edge is always labeled with a URI;
an object node may be unlabeled, or labeled with a URI; a literal node is labeled
with its value.

This simple data model has several serializations - several representations as linear
text. The most commonly used (and the most complicated) utilizes XML. In XML,
nodes and properties are represented by XML elements. The properties of a node element are its
children; each property element has a child, or content in the case of a literal,
representing the value of the property. For example: 

<?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:georss="http://www.georss.org/georss/">

   <rdf:Description rdf:about="http://en.wikipedia.org/wiki/Astoria_Oregon">
       <dc:title>Astoria, Oregon</dc:title>

       <georss:point>46.183 -123.816</georss:point>
   </rdf:Description>

</rdf:RDF>

For more information about RDF, see the RDF pages at W3C.

Simple GeoRSS in RDF and RSS 1.0

In the RDF framework, the content and meaning of Simple
GeoRSS can be
stated in a few words:
georss:point, georss:line, georss:polygon, and georss:box
are RDF properties. Each has a string literal as value, with the detailed
forms as explained on the Simple GeoRSS page.
Asserting that the value of the property georss:point for an
object A

is "lat,long"
means that the geographical location with these coordinates is associated with A.
The nature of the association is left unspecified.
Similarly, the properties georss:line, georss:polygon, and georss:box,
assert the existence of associated
earth-located geometries.

These properties can be used in any RDF context to make simple geographical assertions
about objects. Of particular interest in the current context is the RDF dialect
of RSS:

RSS 1.0. However, there is nothing
special about how GeoRSS properties are used in RSS 1.0 - we need only note that
any of the RSS 1.0 elements can be annotated with GeoRSS properties, including
rss:channel, rss:item, and rss:image. Here is an example:


<rdf:RDF
xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'
xmlns:dc='http://purl.org/dc/elements/1.1/'
xmlns='http://purl.org/rss/1.0/'
xmlns:georss="http://www.georss.org/georss/">

<channel rdf:about='http://www.xml.com/'>
<title>XML.com</title>
<link>http://www.xml.com/</link>

<description>XML.com Articles and Weblogs</description>
<dc:rights>Copyright 2005, O'Reilly Media, Inc.</dc:rights>
<items>
<rdf:Seq>
<rdf:li rdf:resource=
      'http://www.oreillynet.com/pub/wlg/8466?CMP=OTC-TY3388567169' />
</rdf:Seq>
</items>

</channel>

<item rdf:about=
      'http://www.oreillynet.com/pub/wlg/8466?CMP=OTC-TY3388567169'>
  <title>Live Coverage XML 2005 (Tuesday Keynotes)</title>
  <link>http://www.oreillynet.com/pub/wlg/8466?CMP=OTC-TY3388567169</link>
  <description>

	   <![CDATA[A live look at the XML Keynotes and seminal talks.]]>
  </description>
  <dc:creator>Kurt Cagle</dc:creator>
  <dc:date>2005-11-15T07:45:58-08:00</dc:date>
  <georss:point> 46.183 -123.816</georss:point>

</item>

</rdf:RDF>