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Re: An alternative RDF

From: Juan Sequeda <juanfederico@gmail.com>
Date: Wed, 9 Jul 2014 21:58:18 -0500
Message-ID: <CAMVTWDx7128TUPAMbsGJqb=FRcadKHpsiOusW1Y97TzPvJqJ3A@mail.gmail.com>
To: Victor Porton <porton@narod.ru>
Cc: Paul Gearon <gearon@gmail.com>, SW-forum Web <semantic-web@w3.org>
On Wed, Jul 9, 2014 at 2:56 PM, Victor Porton <porton@narod.ru> wrote:

>
>
> 09.07.2014, 22:44, "Paul Gearon" <gearon@gmail.com>:
>
> Others will have a more informed opinion, but if I can address a couple of
> your comments below...
>
>
> On Wed, Jul 9, 2014 at 2:59 PM, Victor Porton <porton@narod.ru> wrote:
>
> As you see from my earlier messages to this mailing list, I had a trouble
> to process data combined from several different RDF files.
>
> Recently I have thought is that (the way I use) RDF is a wrong tool for my
> task!
>
> Consider this Turtle code:
>
>
> <snip/>
>
>
> The trouble is that there may be no more than one :precedence. If we load
> data from an other RDF file, nothing prevents them be merged in such as way
> that there may be more than one :precedence for the same object, so
> rendering data inconsistent and forcing the programmer (me) to do something
> with a data which once was consistent but then suddenly became inconsistent.
>
> In my opinion, this trouble is from essence of RDF itself.
>
>
> Pure RDF provides structure, but very little of semantics. Consequently
> the semantics (such as single cardinality properties) must be provided by
> the application or another layer of modeling such as OWL
> (owl:maxCardinality), which in turn would be enforced by the application.
> RDF is flexible, which allows individuals to encode inconsistent data that
> passes simple validators. This does not make it useless, but does require
> it to be used with care.
>
>
>
> I earlier wrote in this mailing list that I load new RDF files
> dynamically. This may cause that a previously valid data become invalid. I
> don't want my data suddenly become invalid when it was valid earlier (and
> probably already used, so I could not remove it).
>
> It can't be enforced by OWL
>
>

I'm jumping here in the middle so apologies if the following is out of
context or doesn't make sense:


Are you looking for something like Integrity Constraints ala relational
world? If so, then RDF as-is is not the tool for you. I know that there are
some extensions that do support integrity constraints in RDF:
http://docs.stardog.com/icv/

> If you require a data structure where violating cardinality would result
> in a syntax error, then RDF is not appropriate. What you are choosing is
> whether validation is performed by a syntax checker, a model validator, or
> manually by your application. In many situations that decision may be
> arbitrary and a matter of style, rather than leading to some absolute
> notion of correctness.
>
>
>
> Manually by my application.
>
>
>
>
> We should do something either modifying the RDF specification, or creating
> a new formal language to describe objects which cannot be merged from
> several files in an inconsistent way.
>
> One way to solve it inside RDF is to add blank nodes, like:
>
> @prefix : http://portonvictor.org/ns/trans/ .
> <http://example.org/the-transformation> :transformation-data [
>
> <snip/>
>
>         ]
> ].
>
> This way http://example.org/the-transformation becomes an object which
> cannot be "amended" into an inconsistent state by loading one more RDF
> file. We can provide an other data for
> http://example.org/the-transformation but it would be a separate object,
> which may have single :precedence, etc. Even if the second object (sharing
> the same resource URL) is invalid (say has more than one :precedence), the
> first object (above described) remains valid.
>
> However RDF parsers generate IDs (like _:genid1) where unnamed nodes are
> inserted. I am not sure whether a non-appropriate information may be
> inserted from an other RDF file using an ID like _:genid1. (Can it?)
>
>
> I am not certain I have understood your question correctly, but it seems
> that you are asking if by parsing 2 files that contain blank nodes then is
> it possible for them to be accidentally resolved to refer to the same node.
> Is that right? If so, then the answer is no, they cannot. Even if two blank
> nodes are explicitly using the same blank node label, so long as they
> appear in separate documents they will still be treated as different nodes.
>
>
>
> My question is whether I can check programmatically whether a node is
> blank.
>
> <snip/>
>
>
>
>
> Also the last code example is a little ugly: What is a reason to put the
> top-level http://example.org/the-transformation inside
> `:transformation-data [ ... ]` container, while the lower levels of the
> data tree (as presented above) are not in containers? Is it consistent with
> intuition?
>
>
> You have created a transformation that has no identifier, and associated
> it with a named resource that has no information (beyond the
> :transformation-data property). This does not seem to provide any benefit,
> except to make it impossible to accidentally load more data that conflicts
> with the unnamed resource. But as I said above, this should either be
> handled directly by an application, or if you want to automate it then by
> describing with OWL.
>
>
>
> It is exactly the purpose: to make it impossible to accidentally load more
> data that conflicts with the unnamed resource.
>
>
>
>
> So, we need to decide whether we can store such objects in RDF or should
> RDF be somehow amended or even replaced with an other standard. What I have
> described above is a serious fundamental problem and it needs to be
> addressed!
>
>
> --
> Victor Porton - http://portonvictor.org
>
>
Received on Thursday, 10 July 2014 02:59:06 UTC

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