All the data contained in a GN4, Tark4 or GNPortal system is represented in a standard way as XML, GNQuery uses this XML representation to write queries as XPath and XQuery expressions. In other words all the data contained in a system is seen as a virtual XML ‘file’:

 <gn4:story id="obj33478" name="635e2bcd-7803-4a7d-b681-a7d6f865f417" . . .>

   <gn4:title>From mobile 2</gn4:title>

   . . .

 </gn4:story>

 <gn4:story id="obj33476" name="0941b3a9-87ab-4c18-8c17-71270d6600ea" . . .>

   <gn4:title>From mobile 1</gn4:title>

   . . .

 </gn4:story>

 . . . (all other stories) . . .

 <gn4:image id="obj33477" name="image_47a560fd-1d45-4bde-861b-1a2a816c0f99" . . . >

   <title>articleVersions</title>

   . . .

 </gn4:image>

 . . . (all other images) . . .

 . . . (all other objects of different types) . . .

and queries are XPath expressions executed on this XML – e.g. the expression

 gn4:story

returns ALL stories in the system – being an XPath that matches all the story in the above XML. To find a story with a specific title:

 gn4:story[gn4:title='My title']

that is an XPath matching all the gn4:story elements with a gn4:title sub-element containing the text 'My title'.

Query expressions specify objects attributes using their standard XML representation, so in the example above the story title is ‘gn4:title’ – because it is represented as a XML element; to get all the stories modified since August 1st use:

 gn4:story[@modifiedDate>='2012-08-01T00:00:00Z']

because the last modification date is represented as an XML attribute:

 <gn4:story id="obj33476" modifiedDate="2012-14-08T17:33:07Z" . . .>

   . . .

 </gn4:story>

Use the same logic to specify attributes with complex values, for example keywords are represented in XML like this:

 <gn4:story id="obj33476". . .>

   . . .

  <gn4:keywords>

      <gn4:item>architecture</gn4:item>

      <gn4:item>bridges</gn4:item>

    </gn4:keywords>

   . . .

 </gn4:story>

so to find all stories with a specific keyword use:

gn4:story[gn4:keywords/gn4:item='bridges']

To find the stories with ANY keyword use:

gn4:story[gn4:keywords/gn4:item]

i.e. all stories that have at least a ‘gn4:item’ sub-sub-element under their ‘gn4:keywords’ sub-element.

Note that the ‘gn4:keywords’ sub-element is always present – even if the story does not have any keyword, so

gn4:story[gn4:keywords]

is the same as

gn4:story

because the condition inside the brackets is always true.