Re: Alternatives to containers/collections (was Re: Requirements for a possible "RDF 2.0")

On 01/15/2010 04:17 AM, Pat Hayes wrote:
> 
> On Jan 14, 2010, at 3:12 PM, Geoff Chappell wrote:
> 
>> -----Original Message-----
>> From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org] On
>> Behalf Of Pat Hayes
>> Sent: Thursday, January 14, 2010 3:19 PM
>> To: Dan Brickley
>> Cc: Danny Ayers; Steve Harris; Semantic Web
>> Subject: Re: Alternatives to containers/collections (was Re: Requirements
>> for a possible "RDF 2.0")
>>
>>
>> On Jan 14, 2010, at 11:31 AM, Dan Brickley wrote:
>>
>>>> On Thu, Jan 14, 2010 at 4:20 PM, Pat Hayes <phayes@ihmc.us> wrote:
>>>>> A lot, perhaps all, of this hair could be avoided if RDF allowed
>>>>> general
>>>>> tuples as well as triples. All that is needed is some way to put N
>>>>> things
>>>>> into a sequence: so, put N things into a sequence. The 'graph
>>>>> model' would
>>>>> be a hyperlink, drawn as a polygon (eg triangle for N=3) rather
>>>>> than a line.
>>>>> In triples-style syntax, it would just be moving a dot.
>>>>
>>>> I periodically wonder what an RDF without the binary restriction would
>>>> look like.
>>
>>> My 2c suggestions, as answers to the questions.
>>>>
>>>> Would each property/relation have a fixed arity, eg. dc:source might
>>>> 'be a 4', 'foaf:knows' a 7?
>>
>>> No. But it might be useful to distinguish 'really binary' ones, which
>>> only fit in triples, from the others, which can take any number of
>>> things in the sequence. Or maybe not, whatever. But the default should
>>> be, any number (even though most of them will be 2 in practice, ie
>>> triples.)
>>
>>>> That doesn't make a lot of sense to me. So
>>>> presumably they'd vary freely. In which case, we have a lot of
>>>> figuring out to do when wondering whether   livesWith(alice, bob,
>>>> 2007, 'y') implies livesWith(alice,bob) or livesWith(alice, bob, 'y',
>>>> 'foo.html'). The binary straightjacket makes some of these questions
>>>> impossible, albeit maddeningly...
>>
>>> The Common Logic answer is very puritan: each number of arguments is a
>>> separate assertion, and they are all independent (unless you write
>>> axioms connecting them.) So liveswith(a b c) has nothing to do with
>>> liveswith(a b) or with liveswith(a b c d), etc., as far as the logic
>>> itself is concerned.  This is actually quite elegant and works well
>>> WHEN you can write the axioms you might need. So maybe we would need,
>>> for RDF, some way to attach some common inference patterns to these by
>>> giving properties to the property of the tuple. For example, one
>>> useful and common pattern allows ends of argument lists to be lopped
>>> off, so that
>>>
>>> liveswith(alice, bob, <address>, <maritalstatus>)
>>> entails
>>> liveswith(alice, bob)
>>>
>>> and we might specify this pattern (in a semantically extended RDF) by
>>> asserting
>>>
>>> liveswith rdf:type rdf:ExtendableProperty .
>>>
>>> But this is very much off the top of my head. Whaddayathink?
>>>
>>> Pat
>>
>> I wonder how much of this needs to be in RDF itself vs. in query/rule
>> languages that operate over RDF.
>>
>> E.g. we support rules in our sparql extensions and while we of course
>> support rules with triples at the head, we also support ones that have
>> n-ary
>> relations at the head. I find the non-triple variety useful for of course
>> dealing with inferring relations that have a natural arity greater than
>> three but also for just performing transformations without polluting the
>> triple space. Similarly, we have a native list type which is useful for
>> things like accumulating values -- something that would be extremely ugly
>> with a pure triple syntax. In both cases I find the extensions
>> useful/necessary for processing RDF efficiently, but I never really
>> feel the
>> need to push the extensions into RDF storage/graph layer.
> 
> Well, fair enough. After all, RDF does already have what are in effect
> LISP S-expressions embeddable in it, so this is always *possible*. But I
> thought the idea of this thread was to find a way to avoid all this
> pseudo-Lisp list hacking using triples.
> 
> <rant>
> This brings up a broader issue. Everyone agrees its good to keep RDF
> simple. But keeping RDF simple by making it in effect into a
> general-purpose construction kit, and then expecting that as a matter of
> routine people will use the constructions, isn't really being honest
> about 'simple'. OWL/RDF is a lot less simple than RDF itself largely
> because its written in what we might more honestly call
> OWL-syntax-coded-in-lists-described-using-RDF, which IMO isn't really
> RDF any more. If we want to expect RDF to do this kind of thing, then it
> ought to have a whole datastructuring facility built in explicitly,
> perhaps along JSON lines, rather than prostituting the triple store to
> be a data structuring tool.
> </rant>

Wasn't this the whole idea of RDF? Simple language for expressing any
information? Doesn't it use triples, simple relations between two
objects, specifically for the reason that it is universal, and any kind
of structure can be expressed by it? Why should we give preferential
treatment to relations describing structure than those describing time,
measures, events, organizations, people, pizzas...?

This is what I always thought what RDF was supposed to be and things
like containers, blank nodes, literal data types, language tags got in
because of pragmatical reasons, mainly to give users some kind of
direction, examples how to get started.

Reality that even such thing as RDFS was made separate of the RDF itself
support my view (even though I suspect one of reasons if that separation
was the process of it's development).

On the other hand I am not against creating community developed
framework for making common uses of Semantic Web technologies easier,
defining useful structures and design patterns... but build that *on
top* of RDF as separate framework.

I would like RDF to be as lightweight (low level) as possible - if I
were to make mine RDF, there would be no containers, bnodes, literal
data types, language tags, maybe even no literals - using data URI
scheme. Anyway I value compatibility and adoption more than sticking to
my view of the world so I use RDF as it is.

Other alternative would be to have the low level core, build modules on
top of it, for example like some programming languages do (Python,
Java...) and call the whole thing RDF - I guess that is what would make
most people happy.

Best,
Jiri Prochazka

> 
> Pat
> 
> 
> 
>>
>> Rgds,
>>
>> -Geoff
>>
>>
>>
>>
>>
> 
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