Re: RDF/Topic Maps: late/lazy reification vs. early/preemptivereification(was: Re: [topicmaps-comment] RE: OASIS vs W3C)

[Patrick Durusau <pdurusau@emory.edu>]

Steve,

Way cool! 

Interesting side note: The most recent draft of the RDF Model Theory
document, http://www.w3.org/TR/rdf-mt/, does not reach the issue of
reification. (Warning, this is weekend reading, probably from hard copy
with some blank paper at hand.)

Patrick

"Steven R. Newcomb" wrote:
> 
> For me, at least, the shortest, most compelling and
> cogent demonstration of a certain critical difference
> between Topic Maps and RDF was Michael
> Sperberg-McQueen's wrap-up keynote at the Extreme
> Markup Languages Conference (www.extrememarkup.com)
> last August.
> 
> N.B.: This note is about *what I learned* from
>       Michael's presentation, and it does not
>       necessarily reflect Michael's views, or even
>       constitute an accurate account of Michael's
>       presentation.  It's merely what I remember about
>       it.  (I love Michael's wrap-ups at the Extreme
>       conferences.  It's a good thing he traditionally
>       speaks last, because he's a hard act to follow.)
> 
> Michael brought colored ribbons and other paraphernalia
> to the podium, in order to illustrate his words.
> 
> "Tom buttered the bread," was the statement Michael
> wanted to represent.  There being no volunteers in the
> audience named "Tom", Michael appointed our Conference
> Chair, Tommie Usdin, to represent the "Tom" node.  Syd
> Bauman, as I recall, was appointed to represent the
> "bread" node.  A blue ribbon between Tommie and Syd
> represented the arc representing the statement that Tom
> buttered the bread.
> 
>   [Use a monospace font, such as courier, if you want
>   to see the ASCII art as it was intended to be seen.]
> 
>      Tommie -----------> Syd
>      ("Tom")   (blue     ("the bread")
>                ribbon)
> 
> So far, so good.  "Now," Michael said, "What if I want
> to say that Tom buttered the bread with a knife?  In
> order to attach the knife to this statement, I need a
> node for the knife, and I also I need a node to
> represent the buttering itself.  (There must be some
> sort of a 'buttering event' going on here.)"  After
> everyone had finished laughing over our internal
> visualizations of "a buttering event", Kate Hamilton
> was appointed to be the node that represented the
> "buttering event".  A differently colored ribbon was
> used to connect Tommie to Kate, and Kate to Syd.  Now
> there was a triangle of ribbons, because Tommie was
> still *also* buttering Syd by virtue the original blue
> ribbon.
> 
>                 Kate ("the Buttering")
>                  /\
>                 /  \
>                /    \
>               /      \
>              /        \
>             /          \
>            /            \
>      Tommie -----------> Syd
>      ("Tom")   (blue     ("the bread")
>                ribbon)
> 
> Now, with Kate in existence, it was possible
> to use yet another ribbon color to connect the knife to
> Kate (the "buttering event").
> 
> knife --------- Kate ("the Buttering")
>                  /\
>                 /  \
>                /    \
>               /      \
>              /        \
>             /          \
>            /            \
>      Tommie -----------> Syd
>      ("Tom")   (blue     ("the bread")
>                ribbon)
> 
> So now Kate was holding one end of each of three
> ribbons: one to Tom, one to the bread, and one to the
> knife.  Michael then proposed to further modify the
> statement: "Tom buttered the bread with a knife *on
> Friday*".  Yet another volunteer became "Friday", and
> yet another ribbon was given to Kate, the other end of
> which was "Friday".
> 
> knife --------- Kate ("the Buttering")
>               /  /\
> Friday ------+  /  \
>                /    \
>               /      \
>              /        \
>             /          \
>            /            \
>      Tommie -----------> Syd
>      ("Tom")   (blue     ("the bread")
>                ribbon)
> 
> It was clear that Michael could have gone on to attach
> any number of things to Kate; the "buttering event" had
> a limitless capacity to be related to other things.
> Indeed, by the end of Michael's wrap-up keynote, Kate
> was already holding one end of several ribbons,
> including the two ribbons needed to connect Tommie
> (Tom) to Syd (the bread).
> 
> It was also clear that, once "the buttering event"
> existed as a distinct node, it was no trouble at all to
> say anything about that event.  However, *before* Kate
> was appointed to be that node, there was no way to say
> anything about the buttering event.
> 
> After the "buttering event" node represented by Kate
> was brought into existence, the combination of itself
> with its arcs to Tommie (Tom) and to Syd (the bread)
> was sufficient to represent the fact that "Tom buttered
> the bread".  Therefore, once the "buttering event"
> existed, there was no further need for the original
> blue ribbon connecting Tommie (Tom) and Syd (the
> bread).  The blue ribbon was redundant, and it
> unnecessarily complicated the graph of ribbons and
> nodes.  The blue ribbon should go away, right?
> 
> knife --------- Kate ("the Buttering")
>               /  /\
> Friday ------+  /  \
>                /    \
>               /      \
>              /        \
>             /          \
>            /            \
>      Tommie              Syd
>      ("Tom")             ("the bread")
> 
> In Topic Maps, there is no way to say "Tom buttered the
> bread" without creating an explicit "buttering event"
> -- a "buttering association" between Tom and the bread.
> Instead of making a direct connection between Tom and
> the bread, Topic Maps forces us to create a "buttering
> event" node, and to connect "Tom" and "the bread" to
> that node.  The advantage here is that we can always
> say something new about anything that already exists,
> because even the "verbs" in Topic Maps (such as "to
> butter") are necessarily already "noun-ified" (such as
> "the buttering") and are ready to be addressed as the
> ends of additional arcs.  This has significant
> advantages: it simplifies the process of amalgamating
> facts and opinions when you can't know in advance which
> things anyone will want to express a new fact or
> opinion about.  If someone wants to say something about
> "Tom"'s buttering of "the bread", there is guaranteed
> to be something to which those remarks can be attached.
> 
> In RDF, we are not forced to create a "buttering event"
> node in order to say "Tom buttered the bread".  We can
> simply connect "Tom" to "the bread" directly.  This has
> significant advantages if it can be accurately assumed
> that nobody will need to say something about the
> buttering:
> 
> * There are many fewer nodes and arcs to worry about.
> 
> * Perhaps more significantly, verbs remain verbs.  Many
>   people, especially computer jockeys who have not been
>   steeped in the traditions of markup languages,
>   application-independent information interchange and
>   self-describing documents, are more comfortable with
>   verbs (processes) than with nouns.  This is not a bad
>   thing.  It is only the simple truth that, if you're
>   focusing on implementing the application of butter to
>   bread, it would only be distracting and annoying to
>   try to provide for unanticipatable commentaries and
>   constraints on specific "butterings".
> 
> RDF provides a process, called "reification", whereby
> an arc can be alternatively represented as a node when
> it is discovered that someone wants to say something
> about it.  ("Reification" literally means
> "thing-ification" or "noun-ification" -- transformation
> into a thing.  The term "reification" is derived from
> the Latin noun "res" (pronounced like "race"), which
> means "thing".)  When Michael used Kate Hamilton (the
> "buttering event") to be the surrogate of the arc
> represented by the blue ribbon, he was reifying the
> blue ribbon.  The arc became a node (and two new arcs).
> 
> In RDF, reification involves changing the graph that
> results from processing interchangeable RDF statements.
> In Topic Maps, however, everything is already reified.
> No existing arcs need be changed when new information
> comes along.  New arcs and nodes are added, and these
> additions are the only changes that are required.  This
> comparative changelessness can be extremely important.
> If you find something in a graph, and you make a record
> of the arcs you traversed in order to find it, you may
> want to be able to use that same set of arcs to find
> the same thing at some future date.  If some of those
> arcs disappear, you may not be able to retrace your
> steps.  If, on the other hand, the process of
> reification does *not* cause the arcs whose functions
> have been duplicated to disappear, then we have a
> situation in which a considerable amount of redundant
> information is contributing to our infoglut problem.
> Either way, a policy of "late reification" (or maybe we
> should call it "lazy reification") causes problems for
> the usefulness of continuously-amalgamated knowledge.
> 
> Does this mean that I'm pro-Topic Maps and anti-RDF?
> No, not at all!  These two paradigms have great need
> for each other.
> 
> * RDF needs Topic Maps in order to make scalable
>   management of knowledge emanating from disparate
>   sources simple, practical and predictable.
>   Enlightened self-interest dictates that the RDF camp
>   consider Topic Maps as an important and basic RDF
>   application,
> 
> * Topic Maps needs RDF in order to have a popular,
>   widely-accepted basis upon which to describe exactly
>   what a topic map means, in a fashion that will be
>   immediately processable by a significant number of
>   existing and well-funded tools.  The PMTM4 model is
>   an example of a model of the meaning of Topic Maps
>   that can easily be translated into RDF -- once and
>   for all topic maps.
> 
>   If the PMTM4 model is adopted for this purpose, the
>   corresponding RDF arcs will never need to be reified,
>   even the very first time someone needs to make an
>   assertion about a "buttering".
> 
> In the past, I myself have considered RDF as the
> competitor of Topic Maps.  Happily, I was wrong -- at
> least in fundamental technical terms.  Indeed, I now
> believe that if there were no RDF, the Topic Maps camp
> would have to invent something like it in order to make
> the Maps paradigm predictably comprehensible by the
> programmers who are pioneering the development of the
> Internet.
> 
> There are other interesting comparisons to be made
> between RDF and Topic Maps, but ever since Michael's
> demonstration of the difference between early vs. late
> (preemptive vs. lazy) reification, I have been meaning
> to document both the difference and the demonstration.
> Thanks for reading it.
> 
> -Steve
> 
> --
> Steven R. Newcomb, Consultant
> srn@coolheads.com
> 
> voice: +1 972 359 8160
> fax:   +1 972 359 0270
> 
> 1527 Northaven Drive
> Allen, Texas 75002-1648 USA
> 
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-- 
Patrick Durusau
Director of Research and Development
Society of Biblical Literature
pdurusau@emory.edu