Re: Proposing Tracker for inclusion into GNOME 2.18

[Jamie McCracken <jamiemcc blueyonder co uk>]

James Henstridge wrote:
> On 25/10/06, Jamie McCracken <jamiemcc blueyonder co uk> wrote:
> > You would need to completely flatten the metadata as
> > Contact.HomeJabberID, Contact.WorkJabberID etc so that all metadata is
> > mapped 1:1
>
> If you do flatten things like this, I would hope you'd still be able
> to query for people by jabber ID (not caring what role the jabber ID
> is for).  Would that be the case?

yes. currently you would OR the two fields together but if I include the 
metadata relationship stuff then Contact.JabberId can be the parent of 
both Contact.HomeJabberID, Contact.WorkJabberID and so be searched 
automatically.

We are a fine grained metadata database but I accept making it easy to 
do more coarse grain searches is essesntial

> > It would be nice as tracker is a freedesktop thingie to avoid evolution
> > specific naming and also to make it clean and easy for other software to
> > use. Contacts also have relevance to Emails and instant messaging so
> > that kind of software might wanna use these contact objects too.
>
> While having standard names for metadata relationship types that
> everyone can use is great, there are going to be cases where apps want
> to experiment with relationships that haven't yet been standardised.
>
> Would an app be able to do this without modifying tracker?  Is there
> any guidelines about how a project should namespace such metadata to
> make sure it doesn't conflict with what other applications are doing?

the guidlines state that it should be namespaced with the application 
name EG "Nautilus.WindowSize" would be an app specific metadata whilst 
something like "User.Foo" would be a user defined one

> The RDF solution to the namespace problem is to use URIs for the
> property names, which have well understood namespacing to start with.
> Would you suggest apps using tracker do likewise?

possibly although its a bit cumbersome - we could use the dbus way of 
Org.Gnome.Nautilus.WindowSize but im not sure if we need to? Would 
application names overlap?

> > A contact can only have one metadata value per type (this is a primary
> > key constraint)
>
> For a lot of types of metadata you often have multiple values
> associated a single metadata type.  For example, I have multiple email
> addresses.  Having separate "work email" and "home email" metadata
> types might solve the problem in a lot of cases, but what if someone
> has multiple work emails?

if we use the vCard spec for our contacts then it would depend on 
whether vCard supports that?

> > With everything mapped 1:1 you can then use RDF query to search them
>
> Why would you need a 1:1 mapping to do a query?  A query for "contacts
> with an email of jamiecc blueyonder co uk" should be possible
> independent of the number of email addresses a contact can have.

we need the 1:1 mapping to get/set the values. Whatever we implement we 
must have a unique metadata name for a particular service in order to do 
that otherwise getting or setting a value would be impossible.

One problem with metadata relationships is that some metadata like in 
the above case would only be searchable like Contact.JabberID as the 
actual storage would be in Contact.WorkJabberID or Contact.HomeJabberID 
so it might get confusing for developers if they try and get the value 
of Contact.JabberID which would be NULL.



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