Fwd: Question about GML

["Ram Kumar" <kumar.sydney@gmail.com>]

CIQ TC,

Message from OGC about their use of XLINK.

Ram

---------- Forwarded message ----------
From: Carl Reed OGC Account <creed@opengeospatial.org>
Date: Aug 18, 2006 11:48 AM
Subject: Re: Question about GML
To: Ram Kumar <kumar.sydney@gmail.com>


And here is some guidance from Ron Lake, father of GML and XML geek
extraordinaire.

Carl

Hi,



There are some xlink tools - but none of them are very recent nor very
useful.  Any XML parser will parse the xlink attributes.  The question is
then what semantics you apply to them.



The meaning of xlink:href on a GML property is that it is a pointer to the
value of the property.  It plays a similar role to the rdf:resource property
in RDF.  Parsing the value of the xlink:href (a URI) in XML is again handled
by the parser.  The value of the URI may be an arbitrary URI that is a URL
and points to the resource just like in HTML.  It may be a URN (Uniform
Resource Name) that you can use as if it were well known (i.e. do a table
look up in your own software) or it may be passed to a URN resolver that
does the look up for you and provides the resource or a handle to the
resource (perhaps a URL) that use to get the resource.  So for simple xlinks
(most of the usage in GML) you don't meet much in terms of special software.



You may also want to make use of some of the other properties in the gml
Association Attribute Group - in particular gml:remoteSchema.  Parsing is
just as above - but you need to use the referenced resource (a schema
fragment pointer) you will need to fetch the resource as above, apply the
likely XPointer filter contained in the URI value, and then pass the schema
fragment to an XML Schema validating parser.  Again no really special tools
involved.



Where life could get more complex is if the xlink:href or gml:remoteSchema
attributes contain XPointer expressions - especially ones that use string
operators etc. Here there are a number of libraries around that can be used
as starting points. Including:



·
http://www.xbrlapi.org/javadoc/org/xbrlapi/xpointer/package-summary.html

·         http://xmlsoft.org/XSLT/internals.html

·         http://mail.python.org/pipermail/xml-sig/2005-October/011229.html

·
http://skew.org/~mike/4suite-docs/html/modules/Ft.Xml.XPointer.html



I hope that helps!  BTW there are also some libraries and XLink processing
engines (see
http://skew.org/~mike/4suite-docs/html/modules/Ft.Xml.XLink.html)





Cheers

Ron

----- Original Message -----
From: "Ram Kumar" <kumar.sydney@gmail.com>
To: "Carl Reed OGC Account" <creed@opengeospatial.org>
Sent: Thursday, August 17, 2006 3:10 PM
Subject: Re: Question about GML


> Hi Carl,
>
> Thanks for the pointers. Will have a look. We are having problems with
> XLINK
> as there is no support for XLINK in industry and organisations hat
> implement xlink,
> have their own implementations and this is resulting in problems with
> interoperability. CIQ V3.0 is struggling due to this as XBRL wants to
> interoperate with CIQ V3.0 and both these specs. have different
> implementations of XLINK.
> I am sure this will be the case for GML also as W3C does not specifiy a
> schema
> for XLINK.
>
> Regards,
>
> Ram
>
> On 8/18/06, Carl Reed OGC Account <creed@opengeospatial.org> wrote:
>> Hi Ram -
>>
>> All is going well, thank you.
>>
>> Yes, I believe that you can use Xlink with GML. But, not being a XML or
>> GML
>> geek, I do not know the answer to your question. So, I will pass the
>> question onto the GML gurus.
>>
>> In terms of a simple GML profile, a couple of updates:
>>
>> 1. The OGC membership has approved the GML Simple Features Profile. This
>> is
>> a simple - but rich - profile of GML that probably provides more
>> capability
>> than is perhaps required to solve many of the location encoding
>> situations
>> in OASIS. However, check it out at
>> http://portal.opengeospatial.org/files/?artifact_id=15201 .
>>
>> 2. For the majority of simple geometry encoding requirements (point,
>> line,
>> etc), we are working the GML OASIS Profile. I worked up a schema last
>> week
>> for use by Sukumar in the HAVE draft standard. However, it does not quite
>> validate, so I have asked the GML gurus to fix the schemas for me.
>>
>> 3. And of course, there is the really simple GML encoding used in
>> GeoRSS -
>> which is the basis for the GML OASIS Profile. Check out www.georss.org.
>>
>> Also, thought you might be interested to know that the latest version of
>> Google Earth KML uses xAL for expressing Addresses:
>> http://earth.google.com/kml/kml_tags_21.html
>>
>> Cheers
>>
>> Carl
>>
>> ----- Original Message -----
>> From: "Ram Kumar" <kumar.sydney@gmail.com>
>> To: "Carl Reed OGC Account" <creed@opengeospatial.org>
>> Sent: Thursday, August 17, 2006 3:32 AM
>> Subject: Question about GML
>>
>>
>> > Hi Carl,
>> >
>> > How are you?
>> > I have a question for you about GML. I understand GML uses XLINK.
>> > What sort of tools are used to parse XLINK related docs? Any pointers
>> > will be great.
>> >
>> > As soon as your group has produced the XML schemas forcsimplified
>> > version of GML, please let us know.
>> >
>> > Many thanks
>> >
>> > Regards,
>> >
>> > Ram Kumar
>> > OASIS CIQ TC
>>
>>