Re: [SMW-devel] Allowing other extensions to add to RDF export

[Yaron K. <ya...@gm...>]

Hi,
Sure: internal objects are stored using the new parser function
#set_internal, which is called in the following way to define a country's
leader:

{{#set_internal:Is president of|Name=John Adams|Start year=1789|End
year=1797}}

Semantic Internal Objects processes this function by manually adding rows to
the SMW tables, using its own "SIOSQLStore" class:
- a new row is added to the smw_ids2 table, where the object is given a name
like "United States#1".
- new rows are added to smw_atts2 and smw_rels2, for each of the properties
of this object.

Data for internal objects is retrieved by SMW itself; thankfully, the data
in some sense "spoofs" SMW into thinking that it's dealing with wiki pages,
even though they have no entry in the 'page' tables. (It would be better if
SMW could have special handling for internal objects, but that's another
story).

You can read more about it here, of course:

http://www.mediawiki.org/wiki/Extension:Semantic_Internal_Objects

-Yaron

On Wed, Sep 9, 2009 at 3:03 AM, Markus Krötzsch <
ma...@se...> wrote:

> On Montag, 7. September 2009, Yaron Koren wrote:
> > Hi,
> > Sure, let me explain internal objects: they're stored in the SMW database
> > tables the same way that wiki pages are, and they hold their own
> properties
> > the same way wiki pages do; the only difference is that they don't have a
> > corresponding wiki page (and their naming structure, "Name#Number", makes
> > it impossible for there to be a page, since MediaWiki doesn't allow pound
> > signs in titles).
>
> Could you explain a little bit more on how you achieve this internally? How
> are the internal objects encoded during parsing? How are they passed to the
> store? How are they stored? How are they retrieved (e.g. when using
> getSemanticData())? (I am still wondering where to best put the RDF
> generation
> within the overall flow of data.)
>
> Markus
>
> >
> > So I'm imagining the RDF output for an internal object would look like
> > this, for the first internal object in a page called "PageName":
> >
> > <swivt:Subject rdf:about="
> > http://smw.referata.com/wiki/Special:URIResolver/PageName#1">
> > <rdfs:label>PageName#1</rdfs:label>
> > <rdfs:isDefinedBy rdf:resource="
> > http://smw.referata.com/wiki/Special:ExportRDF/PageName#1"/>
> > <property:PropertyName1
> rdf:datatype="...">Value1</property:PropertyName1>
> > <property:PropertyName2
> rdf:datatype="...">Value2</property:PropertyName2>
> > ...
> > </swivt:Subject>
> >
> > ...in other words, it would look like the current RDF for a wiki page,
> > except that it wouldn't contain "swivt:page" or "rdf:type" tags.
> >
> > -Yaron
> >
> >
> > On Mon, Sep 7, 2009 at 2:55 AM, Markus Krötzsch <
> >
> > ma...@se...> wrote:
> > > Hi Yaron,
> > >
> > > I also would like to do some changes to the RDF export in general:
> > >
> > > (1) I would like URI generation to be easier to control in extensions.
> > > The main goal of this would be to make the current "vocabulary import"
> > > feature of
> > > SMW a separate extension, and to allow for other such extensions that
> > > implement better solutions for using external URIs.
> > >
> > > (2) I would like it to become a result printer, so that there is an ask
> > > format
> > > "rdf" that uses the same code as the export Special page. The problem
> > > here is
> > > that RDF export does not export is based on SMWSemanticData objects
> (all
> > > data
> > > for some page) while query printers are based on SMWQueryResult objects
> > > (tabular data based on a fixed set of print requests).
> > >
> > > I guess your changes could go into that re-factoring of the export code
> > > as well. One thing to consider is that the current RDF export is
> largely
> > > controlled by the data value implementations: every datatype can
> provide
> > > its
> > > own way for encoding its contents in RDF (triples, which are then
> > > serialized
> > > to RDF/XML during printout). This is also important to allow SMW to be
> > > used with RDF stores (they get the generated RDF for storing it). So
> care
> > > must be
> > > taken when extending the RDF: it is not enough to insert some string
> into
> > > the
> > > RDF/XML generation, but rather the corresponding RDF triples should be
> > > generated at an earlier stage already so that they are available for
> > > other uses (such as connecting RDF stores) as well.
> > >
> > > So how do internal objects relate to datatypes? In fact, maybe you
> could
> > > send
> > > a short email to explain how internal objects work at the moment.
> > >
> > > Markus
> > >
> > > On Sonntag, 6. September 2009, Yaron Koren wrote:
> > > > Hi,
> > > > I want the new extension Semantic Internal Objects to be able to add
> > > > data about internal objects to the RDF export. Normally this wouldn't
> > > > seem too hard: the function that prints RDF data about a specific
> wiki
> > > > page is OWLExport::printObject(), in the file
> SMW_SpecialOWLExport.php
> > > > (it's a little odd that the class is contained directly in the file
> for
> > > > a special page, but that's another story). Anyway, it seems like the
> > > > solution would be to just add a call to end of that function that
> looks
> > > > something like:
> > > >
> > > > wfRunHooks('smwPrintObjectRDF', array($this));
> > > >
> > > > That way, Semantic Internal Objects could register a function with
> the
> > > > 'smwPrintObjectRDF' hook, so that every time the RDF for a specific
> > > > page was created, SIO could add on the RDF for all the internal
> objects
> > > > in
> > >
> > > that
> > >
> > > > page.
> > > >
> > > > Unfortunately, the problem is that nearly all of the variables and
> > >
> > > methods
> > >
> > > > in the OWLExport class are either protected or private; that means
> > >
> > > there's
> > >
> > > > no way for outside code to add to the RDF. This looks to me like
> > > > overly-protective code; could one or more of the functions be made
> > > > public instead? Or maybe the simplest solution is to create a new
> > > > public
> > >
> > > function,
> > >
> > > > maybe called addToRDF(), that just adds a passed-in string to the RDF
> > >
> > > being
> > >
> > > > generated.
> > > >
> > > > Any thoughts on this?
> > > >
> > > > -Yaron
> > >
> > > --
> > > Markus Krötzsch  <ma...@se...>
> > > * Personal page: http://korrekt.org
> > > * Semantic MediaWiki: http://semantic-mediawiki.org
> > > * Semantic Web textbook: http://semantic-web-book.org
> > > --
>
>
> --
> Markus Krötzsch  <ma...@se...>
> * Personal page: http://korrekt.org
> * Semantic MediaWiki: http://semantic-mediawiki.org
> * Semantic Web textbook: http://semantic-web-book.org
> --
>
>