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Re: Web Semantics of Datasets (v0.2)

From: Ivan Herman <ivan@w3.org>
Date: Mon, 10 Oct 2011 15:03:25 +0200
Cc: public-rdf-wg <public-rdf-wg@w3.org>
Message-Id: <DA8B4D12-1421-4CF3-9408-B8AF76EAC407@w3.org>
To: Sandro Hawke <sandro@w3.org>
Sandro,

I need clarifications on 'R'.

I presume 'R' is a time interval. Does it mean that for any dataset to be valid, a time interval should be defined for it? I guess we can say that if there is no such 'R' as part of a dataset definition, it is considered to be... undefined? 'All Time'?

How does this affect deployed datasets that may have G-s that vary in time already, but where there is no such time definition? Should we require SPARQL 1.1 to have a function that returns 'R' for a given dataset?

I wonder whether we can shy away from mentioning time altogether and accept that fact that <N,G> refers to a name for a G-box, ie, to something that can change over time, and our spec remain silent on this...

Ivan


On Oct 10, 2011, at 13:30 , Sandro Hawke wrote:

> Here's some revised wording for the proposal, getting a bit closer to
> spec text.   It's still somewhat informal, and mixing normative and
> non-normative bits, and best-practice.   And it's not as clear as it
> should be about handling change over time.
> 
>    -- Sandro
> ===
>  A dataset D is true iff (1) its default graph is true and (2) for
>  every pair of <N,G> in D, N names something (a "resource", sometimes
>  called a "g-box") which, at every time T in R, has G as its current
>  state.
> 
>  It follows from AWWW that if N is an IRI which can be dereferenced,
>  a successful, correct dereference of N at any time T in R must yield
>  a serialization ("representation") of G.
> 
>  In order to know whether a dereference occurs at a time in R, it is
>  useful to have R declared in the default graph of D, or in another
>  nearby, easy-to-find data source.  Where possible, is is helpful to
>  have R be All Time; that is, having N name a resource whose state,
>  by definition, never changes.
> 
>  In RDF data, N may be used (1) directly, to name the g-box,
>  expressing things like the license that applies to its state, or who
>  controls it; and (2) indirectly, to refer to G as the current state
>  of the g-box.  Indirect reference can be used to express things
>  about an RDF Graph (a "g-snap"), like that it was the graph some
>  entity asserted at some time.  Indirection is done in the semantics
>  of the predicates with which N is used.
> 
>  When N is used indirectly, the reference to G only holds inside time
>  range R, of course.  Care must be taken not to use N as if it
>  necessarily referred to G, outside of R.  Since R is defined to be
>  the same for all elements of D, indirect reference is safe in the
>  default graph.   
> 
> 
> 
> 


----
Ivan Herman, W3C Semantic Web Activity Lead
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Received on Monday, 10 October 2011 13:02:26 GMT

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