libxml usage

Yewondwossen Assefa assefa at DMSOLUTIONS.CA
Fri Jun 9 11:54:30 EDT 2006

Howard Butler wrote:
> Daniel and Assefa would need to comment on the actual implementation 
> details of using libxml, but on IRC around the time of the SOS RFC, Sean 
> and I suggested the use of an xml library for OxS output instead of 
> using what we derogatorily call "libprintfxml" for this reason. The OGC 
> services code is currently kind of hairy and scary to jump into, 
> especially if you're looking to fix a little output thing or small logic 
> bug here or there.  The use of something like libxml distills things 
> down a little further and affords some additional flexibility that we 
> might not have had without some additional heavy lifting.
> I'd be interested in hearing Assefa's and Daniel's experience with 
> libxml for the SOS development and how enthusiastic they might be about 
> incrementally reworking other areas of the OxS code with it. I'd imagine 
> it would be a somewhat long process, coinciding with revisions to OGC 
> specs to justify the investment, but I am optimistic that the long term 
> benefits would be there.

Things that quickly comes to mind are :
  * learning curve of using the library (at least for the output part) 
is not expensive.
  * It is well supported on different platforms
  * It definitely remove all the formatting/closing tags ... concerns, 
creating an xml friendly environment
  * I have not done any performance tests but It should be slower than 
using the printf directly, although the SOS requests are returned in a 
reasonable amount of time
  * I think It makes it easier to maintain in a long term.

  Saying that, moving all the other Ows and gml services to use an xml 
library is major task.  As you mentioned it will only be appropriate to 
do so if there is a major revision of the service that requires the 
rewrite of the support in Mapserver. Otherwise, It is not always easy to 
justify/fund a rewriting of a module when there are no gains in 
functionality to show for.

> Howard
> At 10:06 AM -0400 6/9/06, Kralidis,Tom [Burlington] wrote:
>> Hi,
>> For the OGC:SOS implementation in MapServer, we opted to use libxml as a
>> means of outputting XML content, as opposed to msIO_printf.
>> Just wondering if there is any comment w.r.t. moving towards libxml for
>> more parts of MapServer.  This would definitely makes things more
>> extensible and allow for more customized output.
>> Comments?
>> ..Tom

Assefa Yewondwossen
Software Analyst

Email: assefa at

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925

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