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Re: Review and Comments for Linked Data Platform FPWD

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Mon, 29 Oct 2012 20:58:57 +0000
Message-ID: <508EEE11.1010205@epimorphics.com>
To: public-ldp-wg@w3.org


On 29/10/12 19:42, steve.battle@sysemia.co.uk wrote:
>
> On 28 Oct 2012, at 20:09, David Wood <david@3roundstones.com> wrote:
>
>> Hi all,
>>
>> On Oct 28, 2012, at 11:23, David Wood <david@3roundstones.com>
>> wrote:
>>> - Section 5.4.8 says that "LDPC servers MUST interpret the null
>>> relative URI for the subject of triples... as referring to the
>>> entity in the request body". I understand why you would want to
>>> do that, but this is another case where implementors should be
>>> expected to scream.  You are asking them to introspect each
>>> triple during ingest just in case it might contain a null
>>> relative URI in the. subject position.  Then you are asking them
>>> to assign a URI for the resource before the parsing is known to
>>> be valid...
>>
>> The more I think about this, the more I think that this is a real
>> problem for implementors.  Load speeds are always an issue and this
>> would make things much worse.
>
> David, no introspection is required, implementors would parse the
> POSTed RDF serialization with the document base set to the created
> resource URI. Expansion of the null relative URI proceeds according
> to the usual semantics of the language (at least for Turtle and
> RDF/XML).

But it does assume that parsing is not done immediately that data is 
received as might be natural when systems separate the basic request 
handling from the

>
> Admittedly generating the pesky null relative URIs on the client side
> presents a problem for many of today's tools - not entirely sure
> why.

Because to create RDF, you need absolute URIs.  Creating RDF without 
absolute URIs is not what normal tools support.  It requires fakery 
(rewrite on output) or addition, non-RDF, assumptions about the tools. 
And no use of N-triples.

>
>>
>> Would the WG accept a compromise?  I propose that clients MUST
>> inform servers if they expect null relative URIs to be placed with
>> the newly created URI for the resource.  That way, servers only
>> need to incur the cost of the extra parsing and computation when
>> they are told they need to do it.  Does that work?
>
> In that case, how otherwise would we refer to the subject of the
> resource creation? The URI is unknown at the time of the POST.

Why not POST to create the new resource, using an empty body, get the 
URI back "Location:"), then PUT the contents?  c.f. 303 roundtrip.  Then 
the RDF to be stored can be created after the URI is allocated and 
standard toolkits can be used.

This also allows you to POST the entry in the container - or POST to the 
container itself, c.f. ?non-member-properties.

	Andy

>
>>
>> The flag can be passed to the server on the PUT URL by appending
>> ?updateNull or some such.
>>
>> Regards, Dave
>>
>>
>
>
> Steve Battle
>
Received on Monday, 29 October 2012 20:59:27 UTC

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