[Openstreetmap-dev] More on GPX schema
steve at asklater.com
Sun Sep 25 00:20:52 BST 2005
* @ 23/09/05 01:18:21 PM immanuel.scholz at gmx.de wrote:
> Hi again,
> > That is, that each think that can have metadata just has a string up to
> > 255 chars in length associated with it like tags in flickr or
> > del.icio.us.
> I've read the future: 255 limit will be way to short. ;-)
Yeah, replace it with 16 instead of 8 bits then.
> >> Or are key/values the final feature? :*)
> > With a string you can tag, or whatever you like.
> Of course, you can convert every idea to a string-textual representation
> and try to squeeze it in 255 chars. But maybe people want features that
> are better expressed a different way?
> Hm, lets find an example....
> Maybe an tag that states how long this entry will be valid (for points of
> interest). Now you want to do a query on the server: "Gimme all events,
> that are valid at least until christmas."
> You'll do hard to do this in acceptable performance (means: not by getting
> everything and parse every metadata for the "valid" - tag, extrakt the
> date after, convert the string-date to a real date and compare it.)
This is really a searching-the-tags problem, something I'm not terribly
willing to leave to the database as they tend to be unbearably slow.
Some caching search table or something independent like Lucene but not
java would be great.
> I don't say that people will or will not change key names to senseless
> values. But I say that if people change keys and keys are in the
> xml-structure, not in the xml-data, than you've got a problem...
Yeah, thought of that and then decided not to think about it until it's
time to start writing the sanity checking code for it.
> > immi++
> "Imi" (note the only one "m") comes from an old and forgotten cleaning
> agent from DDR. ;-)
> If you hold key/value pairs in seperate columns of a table, you can query
> much faster on things like: "Gimme all 'Autobahn's". You loose the free
> structure this way however but now you are able to attach metadata on
> keys, maybe making your meta-metadata idea obsolete?
Seperate columns is good, but it makes the SQL more painful and you
loose the simplicity...
SteveC steve at asklater.com http://www.asklater.com/steve/
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