[Dev] RDF tax

David McCusker david at osafoundation.org
Fri Nov 15 13:04:52 PST 2002


Bill Seitz wrote:
> http://bitworking.org/Nov2002.html#X631728215834883232
> 
> Which may or may not be relevant

Below I cite a small part of that material by Joe Gregorio so I can
comment on the use of RDF in Chandler, since apparently some folks
are concerned about paying the RDF tax, and worry this will make the
Chandler framework(s) complex.

Joe Gregorio (http://bitworking.org/Nov2002.html#X631728215834883232):
: Note that mail in Mozilla is stored in mbox format and that there is
: a seperate code layer above it that presents it as an RDF data source.
: They didn't go back an change the mbox format so that it was native
: RDF. This is very important because it leaves the mbox format alone
: allowing the current set of tools that manipulate mbox format to still
: work. I'll repeat that for emphasis: They left the native format alone.
: This is very different from picking up a working format and forcing
: into a convoluted form so that it is natively RDF. We all know how
: successful that's been.

Chandler content will not typically be stored in any native RDF format,
although it makes sense to generate some on demand when this is what
the user wants.  (Say, if a user wants to see addresses represented as
an RDF serialization, why not do this when requested?  It need not
imply anything about how the content is stored the rest of the time.)

As Joe Gregorio mentions, mail in Mozilla is stored in mbox format, and
yet the content is still presented at some higher level as RDF content.
Chandler can store content in any physical encoding it wishes and still
present content as RDF compatible in every suitable context.

We're currently thinking along the lines of transparent Python object
persistence for Chandler, which might also make this content visible
in other ways when accessed along a more direct route than straight
through the Chandler app framework interfaces.  The persistant object
format won't have any character specific to RDF.

And yet, we also want RDF schemas which can describe all the content, so
Python objects are visible in an RDF world that can query and otherwise
deal with the content as if it has a native RDF representation somewhere.

So Chandler will use RDF in the sense that when someone wants to operate
on content with RDF based interfaces (including internal Chandler view
components) this will work in a highly supported way, especially since
Chandler will depend on this working well itself.

However, this doesn't mean RDF in any way determines what can be stored
persistently, or what it looks like to a reader or writer when an RDF
based interface is not the one desired.

The RDF tax won't get you when you want to avoid it.  Of course, some
folks will want to understand the internals of Chandler intimately, and
using RDF internally implies a need to understand how RDF gets used in
Chandler contexts.  That will be a barrier to entry if RDF complexity
stops new folks from getting involved, or old folks from understanding
how to solve problems as they crop up in development.

So I'll try to make sure the RDF parts have a description that it easy
to understand, so the barrier to entry is a low as possible.  I'm not
sure how I'll do that yet, but it doesn't sound hard in principle.

Probably this means I'll write an RDF primer suitable for Chandler that
aims to make it sound simpler than other documents do.  (I have not yet
read the recent documents whose links were posted by Wes Felter; see
http://lists.osafoundation.org/pipermail/dev/2002-November/000250.html
which includes the following links:

http://www.w3.org/TR/rdf-concepts/
http://www.w3.org/TR/rdf-primer/
http://www.w3.org/TR/rdf-mt/
http://www.w3.org/TR/rdf-schema/
http://www.w3.org/TR/rdf-syntax-grammar/)

The last time I spent a lot of time thinking about RDF when I was at
Netscape, I thought of a spatial interpretation of RDF graphs that might
or might not be helpful when I rethink it and write a description.  But
even more important might be an explanation of how it relates to Chandler
content without overwhelming a reader with RDF specifics.

Maybe I'll describe an in-memory representation that emphasizes space
efficiency that is easier to grasp for coders than grammars about the
text serialization formats.  Diagrams might clarify things later.

Anyway, I hope to keep RDF from making Chandler hard to understand when
folks want to get involved.  But the engineering for persistence in the
system is only now getting underway for the long term production plans,
so I can't tell you yet how I'll achieve the desired effects I mentioned
concerning independence from the RDF perspective.

--David McCusker




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