Re: [Tracker] tracker RDF data

[Jamie McCracken <jamiemcc blueyonder co uk>]

Eyal Oren wrote:
> On 07/19/06/07/06 15:54 +0100, Jamie McCracken wrote:
> > Eyal Oren wrote:
> > tracker is not designed for use as a web service but as a desktop 
> > service (hence dbus is used).
> I know, that's good. RDF is definitely not only for the web.
>
> > Its also not an RDF style application it merely uses RDFQ (xml based 
> > version) as a means to query stuff. We dont implement all of RDFQ but 
> > a subset with extensions. We also only uses the <rdfq:Condition> parts 
> > in the query so its not a full blown RDF thingy. (you can see rdf 
> > query examples in the tarball in the rdf-query-examples folder)
> ok. but your datamodel is exactly like RDF: desktop-object has-property 
> with-value, e.g. (file-abc creation-date 2006/01/01), or (contact 
> hasName 'jamie') seems exactly the same as the RDF model (subject 
> has-predicate with-value), which is not so strange, because RDF was 
> designed to be a simple and generic datamodel and directed graphs are 
> then a natural solution.


Yes I know all that. There are things about RDF (like hierarchical 
types) which I find inelegant and convoluted so i have basically taken a 
cleaner simpler approach.

The datamodel is generic enough for RDF use as well as LDAP and other 
object databases - they all have a similiar tree like table structure.

> I don't mean to say that you should internally use RDF, since e.g. MySQL 
> is certainly more developed than current RDF databases. But what would 
> be useful is to align terminology, as you do in the 'shared file 
> metadata spec'. As you state there, the only requirement is that 
> metadata names are unique and not overloaded:
> If I say 'file-abc is-owned-by EyalOren' and you say 'file-abc has-owner 
> EyalOren' then we have a problem merging and combining those two pieces 
> of metadata, and that's why you want to standardise the naming of these 
> metadata indicators (called properties in RDF).
>
> The thing is that in RDF a lot of work has been done into standardising 
> exactly such vocubalaries. Such schemas could possibly contain 
> indications on domain/range of those properties, e.g. has-creator 
> usually relates files to persons.  See for example schemaweb [1] for 
> some existing schemas (the PIMO schema [2] used by gnowsis is very 
> relevant, but the document is very long and winded.
>
> If you are interested, I would certainly be interested to figure out how 
> we can better align the existing schemas in the RDF world with your 
> 'shared file metadata specification'.

Im not sure - I did look at it before and found it too complex for my use.

> Of course, if you're not interested in that, I can easily do the 
> tracker-terminology-to-rdf-schema-vocabulary translation myself, in the 
> adapter (as we did for evolution data: we mapped it to FOAF [3] and some 
> other RDF schemas).

okay


> > The dbus stuff will need Ruby bindings (if they exist?). Queries are 
> > returned via dbus as a native dict/Hashtable  with the URI as the key 
> > and an array/list of values as the contents. I expect if you were 
> > going to make use of it you could serialise this into ntriples yourself.
> Yes, the triples are no problem, but the ruby dbus bindings are very old 
> and seem to be deserted. I don't really know how to get that working, I 
> don't know anything about dbus myself, so I don't see myself writing 
> those bindings.

All I have seen is http://rubyforge.org/projects/dbus-ruby

> > Im not sure if the above helps or not but it sounds like it would need 
> > some mods on your part to make use of it.
> Yes definitely. If I can get the dbus stuff to work somehow, I can 
> easily do the rest.
> What kind of queries can I send to 
> org.freedesktop.Tracker.Search.Query?  Which subset of RDFQ do you 
> support exactly?

I will document this in due course. In the meantime please look at the 
examples here:

http://cvs.gnome.org/viewcvs/tracker/rdf-query-examples/

Note only the stuff between the <rdfq:Condition> tags is parsed and used 
in the next version.





--
Mr Jamie McCracken
http://jamiemcc.livejournal.com/