[gdal-dev] Re: [gfc-dev] GFC

[Frank Warmerdam]

Liujian Qian wrote:
> The thing is, even with the meta query mechanism you described below, if the
> application code is not specifically aware of the format, how does it know
> what names can be used to fetch the metadata associated with them? The problem
> is that if you define a set of metadata names for each format, you quickly
> lose the purpose of metadata, unless some sort of standard tags or metadata
> names have been estabilished. Don't get me wrong though, I consider metadata
> query/managment to be very useful to GDAL (and probably GFC as well),
> for instance in the internal organization of format drivers, and isn't it
> always nice to have a database of meta data about all the formats GDAL
> understands. Hey you probably can add a GDALMetaManger to
> maintain some kind of meta specification for each concrete GDALDataset
> class.

L.J.,

Good point. Certainly the flaw with the OGDI updateDictionary() has been
that you had to purposefully decide to query for particular aspects. In
GeoGateway there was an easy mechanism to get all the metadata, and presumably
there would be within GDAL as well.

> This also gets me thinking about a flexible metadata management mechanism.
> I think XML-based approach is a serious candidate. It is hiearchical and
> it's just sooo flexible. And yeah you can have all the type information
> in there as well. I just coined an example below for some LADSAT images :

This is an excellent point. In fact, I believe that OGDI is moving to 
handling some types of metadata as XML for the very reasons you indicate.
In retrospect, I will think a XML organization of metadata is an excellent
idea. 

This will add some weight to GDAL in the form of an XML parsing library,
but I am lead to understand that a proper XML parser can be quite light,
and that there are at least a few in the public domain (or reasonable
licensing terms). 

When I get to this I will look into it further. Do you have any pointers
to web pages on the use of XML for geographical metadata, or to an OpenSource
XML parser?

Best regards,

-----------------------------------+---------------------------------------
Who can give them back their lives | Frank Warmerdam, Software Developer
and all those wasted years? - Rush | URL http://members.home.com/warmerda
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