MapServer and XML...

[Doug Nebert]

imap at chesapeake.net wrote:

> 
> Doug, Can you provide a URL reference to the OpenGIS XML topics?
> I looked thru the list, but no mention of XML on the index page.
> 

The Web Mapping Service specifies each server's "capabilities" using a 
hierarchical markup in XML for the server and a repeating section for 
each "layer" which is analogous to named layers in mapserv. This 
capabilities.xml file can be placed at a WMS server site for harvest 
into a services registry (so we know what map servers exist) or for 
interrogation by middleware or a smart client to offer layer choices to 
a user. See the WMS Get Capabilities interface specification.

Also, any day now, the Geography Markup Language (as Recommended Paper) 
will be available for public review. It is not a specification, and 
despite the apparent similarity to a W3C "Recommendation", this is only 
a first step towards a future spec. GML has several flavors of 
implementation, but essentially encapsulates mapped Features, their 0- 
1, and 2-D geometries, and attributes using XML markup. It is intended 
for use where a client wishes to cache objects for display and query 
without re-visiting the server and could be viewed as a type of export 
format for extracted or full vector data. The next phase of Web Mapping 
Testbed will take GML further towards a specification, but soon the 
recommended paper will be available for you to experiment with.





> Moving to an XML config is probably the way to go, but guaranteed to
> break the existing applications that use the old mapfiles.  That
> would be painful to change all those mapfiles I have all over the place.
> Maybe a mapfile->XML conversion tool would be the ticket... or some way
> to accomodate either configuratoin as a stop-gap measure.
> 

Supporting either might be a good idea.





> I dont know for sure, but I suspect that XML is versatile enought to support
> all of the baggage we carry in the mapfile.  Maybe we can come up with some
> concrete examples of how this might look?   What this boils down to, is nested
> map objects (and the objects which make up a map) and if XML can support that,
> it would make perfect sense to persue that goal.
> 

XML most certainly stores hierarchies of information (think outline) 
with repeated groups, most elements having a starting and ending tag. 
The creation of a "rule" document, called a DTD, would help enforce or 
validate the map file. One quirky thing, but some parsers are very case 
sensitive, so the case of the tags you declare matters... See attached 
example of the demo map file manually converted to XML. Don't 
necessarily trust my assignments, but by defining these rules of 
encapsulation it will make the composition and testing of map file 
contents better.

Doug.





> Regards,
> 
> Chris Stuber (mapsurfer)
> Silicon Mapping Solutions, Inc
> 410.257.3187
> 
> 
> 
> Stephen Lime wrote:
> > 
> > Greetings all. I'd like to start a discussion concerning the relative merits of moving
> > MapServer configuration files from the ad hoc formats they currently exist in to XML.
> > Lot's of good reasons to do this, validation being one. Just thinking out loud and
> > looking towards version 4.0. Comments appreciated.
> > 
> > Steve
> > 
> > Stephen Lime
> > Internet Applications Analyst
> > 
> > Minnesota DNR
> > 500 Lafayette Road
> > St. Paul, MN 55155
> > 651-297-2937
> 
> 
> 



--
Douglas D. Nebert
Clearinghouse Coordinator
FGDC Secretariat	Phone: +1 703 648 4151	Fax: +1 703 648-5755	
Pager Messaging: 	http://clearinghouse3.fgdc.gov/dougmsg.html

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