Re: PATCH Use Case and Implemented Proposal

On 08/09/13 16:37, David Wood wrote:
> On Sep 7, 2013, at 22:39, Sandro Hawke <sandro@w3.org 
> <mailto:sandro@w3.org>> wrote:
>
>> Thanks for something so concrete, Dave.   For myself, much of the 
>> challenge here is that I've not had time to implement, so it remains 
>> too abstract.    Some questions and thoughts, inline....
>>
>> On 09/07/2013 09:09 PM, David Wood wrote:
>>> Hi all,
>>>
>>> The need for a PATCH format for LDP was brought up again in last 
>>> week's meeting with TimBL [1].  To summarize briefly, Tim made the 
>>> point that LDP has no generic way to update data without a PATCH 
>>> format and Arnaud said that the WG wanted one but hadn't yet been 
>>> able to define it.  Arnaud called for a halt on PATCH formats in May [2]
>>>
>>> The two main approaches would seem to be Andy's proposal [3] which 
>>> uses basic triple patterns to define what to add or remove from a 
>>> store and Sandro's TurtlePatch [4].
>>>
>>
>> I also did a Trig-based patch format, DataPatch: 
>> http://www.w3.org/People/Sandro/datapatch but like TurtlePatch I 
>> haven't actually been pushing it. But it was going the direction the 
>> WG said it wanted to go, using TriG.
>>
>>> This message suggests a third approach based on a strictly defined 
>>> subset of SPARQL Update
>>
>> Isn't that exactly what TurtlePatch was?
>
>
> Yep, sloppy phrasing.  Sorry.
>
>
>>     True, your subset is somewhat..
>>
>>> .  Our approach is already implemented in the (Apache 2 licensed) 
>>> Callimachus Project [5] and documented later in this message.  Henry 
>>> has already mentioned that a subset of SPARQL Update could work [6] 
>>> for the WG's purposes.
>>>
>>> A strict subset of SPARQL Update is used in the Callimachus 
>>> implementation to support the following constructs in a 
>>> PATCH request. However, each clause can only contain zero or more 
>>> basic graph patterns and only the default graph can be used.
>>>      * DELETE DATA
>>>      * INSERT DATA
>>>      * DELETE WHERE
>>>      * INSERT WHERE
>>>      * DELETE INSERT WHERE
>>>
>>> Callimachus further restricts the SPARQL Update spec such that all 
>>> nodes are connected and all URIs, in the subject position, before a 
>>> '#' (if present), are the same.
>>>
>>
>> What's the reasoning behind this?   I've always assumed that a basic 
>> requirement of Patch was that it be able to patch any RDF graph to 
>> any other RDF graph (given enough computing resources).    Is there 
>> some other requirement that necessitates this restriction?
>
>
> It seems obvious to me that in the context of a REST API you don't 
> want to be able to allow the addressing of one resource to be be able 
> to be used to update another.  So, security and the making of 
> intention concrete are good reasons.  Another is that this approach is 
> easier to validate against the target URI.

That makes sense for LDP.

Does the format allow finding that resource by pattern, not just with a URI?

INSERT { ?this : 123  }
WHERE { ?this   :InverseFunctionalProperty "key" }

>
> Regards,
> Dave
> --
> http://about.me/david_wood
>
>