[XESAM] Questions regarding Xesam Query Language

[Mikkel Kamstrup Erlandsen]

2007/9/17, Mikkel Kamstrup Erlandsen <mikkel.kamstrup at gmail.com>:
>
> 2007/9/17, Anders Rune Jensen <anders at iola.dk>:
> >
> > 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...

Cheers,
Mikkel
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