2007/9/17, Anders Rune Jensen <[EMAIL PROTECTED]>: > > On 9/17/07, Mikkel Kamstrup Erlandsen <[EMAIL PROTECTED]> wrote: > > 2007/9/17, Mikkel Kamstrup Erlandsen <[EMAIL PROTECTED]>: > > > 2007/9/17, Anders Rune Jensen <[EMAIL PROTECTED]>: > > > > > > > Hi > > > > > > > > I've been reading the Xesam Query Language specification and I have > a > > questions: > > > > > > > > 1) How do I get all tags for all files? Preferable as list<name, > > > > count>. The same is true for other attributes such as mime-types. > > > > > > > > > You are right that there is no obvious way to do this atm. I think the > > best solution is to simply add a new selector called "any", and use it > like > > the following. > > > > > > Firstly note that the ontology does not yet implement Tags as first > class > > objects, but this is on Evgenys todo I believe. Since this is not ready > yet > > consider the following an example only. > > > > > > Assume that the Tag objects has a field xesam:tagName. The return type > for > > GetHits is controlled via the session property hit.fields, so if you > set > > this to [xesam:tagName] and do the query > > > > > > <request xmlns=" > > http://freedesktop.org/standards/xesam/1.0/query";> > > > <query content="xesam:Tag"> > > > <any/> > > > </query> > > > </request> > > > > > > GetHits will give you all all known Tag names. If you want the count > for > > each tag I see two solutions. Either the ontology should define a field > > xesam:memberCount or something like that, or you create a new search for > > each tag like > > > > > > <request > > xmlns="http://freedesktop.org/standards/xesam/1.0/query";> > > > <query content="xesam:Tag"> > > > <equals> > > > <field name="xesam:tagName"/> > > > <string>TAGNAME_HERE</string> > > > </equals> > > > </query> > > > </request> > > > > > > and simply issue GetHitCount on each search and then close it. This > should > > actually be fairly efficient on most backends. > > > > > > It should be noted that tagging and tag management as such might be > hard > > to implement completely in the search API. The search API is mainly > > targetted at "search" :-) In XESAM iteration 2 we will focus on a > metadata > > management API where such things might be more natural. > > > > I just realised that my answer above does not answer your question about > > mime types and other similar things you might want to list. > > > > I think what you ask for is a way to request all different values for a > > given field. I'm not 100% sure that all implementations can support this > > effectively. Lucene does not support this AFAIK. > > > > Another thing is the use case... In the case of mime types why can't you > use > > the conventional ways to get a list of known mime types? Why would you > > generally want to list all known values of a field? I'm thinking some > > clustered browsing or something... > > The use case would be something like a music program where you would > like to know what audio types is stored on the hd (mp3, ogg, flac > etc.) and then add only those as buttons so the user can for example > select only flac files. Also it could be nice to know how many flac > files there where before clicking the flac button. In particular > because the result list might be limited to a certain number of > results (and because getting the total number (just the count) of flac > files this way is inefficient ;-)).
In this case I think it is perfectly OK to spawn a search for each supported audio mime type and issue only a GetHitCount call on each search before you close it (if we are talking < 10 or so). That should be quite fast on all backends since there is no real data transmission going on. Moreover if the hit data is only fetched lazily (like Lucene (and Xapian I believe)) then the overhead of requesting a few hit counts is really small. I don't know how fast Tracker would be here, but I suspect plenty fast. Cheers, Mikkel
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