[Mulgara-general] Models, inferencing, etc.

Paul Gearon gearon at ieee.org
Wed Aug 26 12:34:46 UTC 2009


OK, I wanted to answer this email too, but it's going to take a LONG
time, so I have to put that off for now.

Just as a quick response....

- Yes, it's confusing.
- Yes, we need to document it.
- Graphs and models are synonymous

Once upon a time everyone called them "models". But then we started to
build "Models" using OWL, and then we had models at different
conceptual levels (like M0 and M1 in the MOF, if you know that). So to
distinguish between the data "model" people were creating, and the RDF
expression of data, the RDF stuff changed terminology to say "graph"
instead.

Unfortunately both Jena and Mulgara had HUGE amounts of code that
referred to "Model", and lot of this appeared in names in the external
interfaces. This meant that the name couldn't just be changed
overnight (else we'd break everyone's code). But anything new should
be called "Graph". Both us and Jena would like to change over to using
Graph exclusively.

Dataset is a more generic name for referring to a block of data, and
tries to avoid the issue altogether.  :-)

I'll write more later. (probably next week, when I have a permanent
internet connection again)

Regards,
Paul

On Tue, Aug 25, 2009 at 5:38 PM, Gregg Reynolds<dev at mobileink.com> wrote:
> One thing that is confusing for newcomers to the world of RDF and OWL etc.
> is the lack of a standard terminology for, uh, well I'll call it reasoning
> services.  We have at least the following terms:
>
>  Reasoning services
>  Inferencing services
>  Entailment
>  Descriptive logic
>   and etc.
>
> To go with this, different implementors refer to RDF "stuff" in different
> terms.  SPARQL refers to "RDF Datasets" and "graphs"; Jena documentation
> refers to graphs but uses "model" to mean graph (in addition to various
> other things); Mulgara uses both "graph" and "model", but not "dataset", so
> far as I know.
>
> This proliferation of quasi-technical terminology is a big problem for
> noobs.  What's the difference between a reasoning service, for example, and
> a rule engine?  How does RDFS validation relate to OWL? Where does Mulgara
> fit?  Etc.
>
> Now Mulgara's documentation regularly uses the term "graph" in the way I
> would expect; but then it uses the term "model" in various ways, such that
> it's hard to tell the difference.  For example, TQL "create" takes a "type"
> parameter, which is taken to refer to various "types" of models, not graphs.
>  Quoting from http://www.mulgara.org/trac/wiki/Create:
>
>    "http://mulgara.org/mulgara#Model  This is the default triple store
> graph."
>
> So, which is it , a graph or a model?  My inference is that Mulgara uses
> "graph" and "model" as synonyms; true?
>
> As a general principle, I would propose that any RDF project adhere strictly
> to the terms "dataset" and "graph" as used in the SPARQL spec, and be very
> careful about "model".  At least in the documentation; obviously you can't
> change APIs willy-nilly.
>
> Now I did dig around in the sources and found the documentation on
> inferencing, which seems to be a good start.  In particular,
> /docs/site-src/inferencing/infermulgara.html clears things up a little bit.
> It sounds something like what is described in the Jena documentation for the
> Ontology and Inferencing APIs, which, uh, makes sense.
>
> So I guess my question is this: is there a reason (other than lack of time)
> that isn't on the wiki, or more polished?  IOW, I don't want to run with it
> (improve and wikify it) if it's all in a state of flux.
>
> Maybe a first task for the developers would be to go through the existing
> documentation and indicate what is obsolete and what isn't.
>
> A sugggestion:  put the technical documentation into Docbook.  I for one
> like to be able to print out a print-formatted copy of documentation; with
> Docbook you get both HTML and PDF output for free.  You can find a superb
> (quasi-free) docbook editor at http://www.xmlmind.com/xmleditor/ (no
> relation to them, I just like the editor).
>
> Thanks,
>
> gregg
>
>
>
>
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>



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