[Versa] Versa issue: subgraph primitives?

[Uche Ogbuji]

On Sun, 2005-08-14 at 22:53 -0600, Michael Olson wrote:
> On Aug 13, 2005, at 7:40 AM, Uche Ogbuji wrote:
> 
> > For a long time I (and apparently others) have felt that we really
> > should have statements as first class objects.  I'm a bit less sure,  
> > but
> > think we should consider having subgraphs as first-class objects.
> >
> > Chime, responding to Kyle, offers some useful discussion along these
> > lines:
> >
> > http://lists.fourthought.com/pipermail/4suite/2004-October/012919.html
> >
> > IMO, if we accept subgraphs as first-class objects, then we should dump
> > statements as separate first-class objects.  A statement is, of course,
> > just a special case of a subgraph.
> >
> > Traversal expressions would return a subgraph rather than a list of
> > statements (or scalars right now).  As chime says, this would allow for
> > very elegant composition, e.g. in chaining Versa queries.
> >
> 
> Which ever route we choose to call it isn't list(statement) = sub  
> graph?  Since lists are first class objects....

Yes, except that it might be more properly a set (not entirely sure on
that one).


> I guess, since in Versa just about everything is a list, then we really  
> do have sub graphs as first class objects.  I still think we need to  
> define what
> 
> item({sub-graph expression},0)
> 
> returns though.  I don't think it can be another sub-graph of length 1.

I think that for 2.0 this is where Chime's suggestion of Python slice
syntax+semantics comes in (for lists rather than sets, of course).


-- 
Uche Ogbuji                               Fourthought, Inc.
http://uche.ogbuji.net                    http://fourthought.com
http://copia.ogbuji.net                   http://4Suite.org
Use CSS to display XML, part 2 - http://www-128.ibm.com/developerworks/edu/x-dw-x-xmlcss2-i.html
XML Output with 4Suite & Amara - http://www.xml.com/pub/a/2005/04/20/py-xml.html
Use XSLT to prepare XML for import into OpenOffice Calc - http://www.ibm.com/developerworks/xml/library/x-oocalc/
Schema standardization for top-down semantic transparency - http://www-128.ibm.com/developerworks/xml/library/x-think31.html