Re: Comments on the LDP Spec: Creating new Resources

On Thu, Oct 9, 2014 at 4:34 PM, Miguel Aragón <miguel.aragon@base22.com> wrote:
> Oh, please tell me why :)

Because that is not how the group decided how to do things?

Pardon me if I sound condescendant, really, but what you are doing
with your platform (driving the interaction with RDF) was discussed
*many* times in this working group and what came out of this is
fundamentally not what you are describing. The specification is very
clear on that. See the pointer I gave earlier.

What you are asking is something very different than what is achieved in LDP.

Alexandre

>
> On Oct 9, 2014, at 3:33 PM, Alexandre Bertails <alexandre@bertails.org> wrote:
>
>> On Thu, Oct 9, 2014 at 4:32 PM, Miguel Aragón <miguel.aragon@base22.com> wrote:
>>> In our server resources are basically named graphs that contain a resource that shares the same name as the graph and additional resources that extend that resource (think, # resources). So for us, if you send a document like: [[ <somethingElse> a ldp:RDFSource. ]] to the URI: http://example.org/container/ we take that as if you are trying to create:
>>>
>>> graph <http://example.org/container/somethingElse> {
>>>        <http://example.org/container/somethingElse> a ldp:RDFSource.
>>> }
>>>
>>> That’s the way our platform works (not the way I think).
>>
>> Ah, then I am afraid that this is just not LDP...
>>
>> Alexandre
>>
>>>
>>> On Oct 9, 2014, at 3:27 PM, Alexandre Bertails <alexandre@bertails.org> wrote:
>>>
>>>> On Thu, Oct 9, 2014 at 4:24 PM, Miguel Aragón <miguel.aragon@base22.com> wrote:
>>>>> I’m sorry Alexandre, could you elaborate? I didn’t understand your response.
>>>>
>>>> Sure, but let me ask you a question first. You seem to think that the
>>>> presence of the triple [[ <somethingElse> a ldp:RDFSource. ]] in what
>>>> you post should create the resource <somethingElse>, module relative
>>>> URI resolution.
>>>>
>>>> Is that what you think?
>>>>
>>>> Alexandre
>>>>
>>>>>
>>>>> On Oct 9, 2014, at 3:21 PM, Alexandre Bertails <alexandre@bertails.org> wrote:
>>>>>
>>>>>> On Thu, Oct 9, 2014 at 4:18 PM, Miguel Aragón <miguel.aragon@base22.com> wrote:
>>>>>>> Hi Dave,
>>>>>>>
>>>>>>> I’m ok with that, I just don’t want the LDP Spec to force us to support null
>>>>>>> URIs and relative URIs without a base.
>>>>>>>
>>>>>>> If that’s the case then the LDP test suite needs to be modified because it
>>>>>>> sends both null URIs and relative URIs without a base (which may not be
>>>>>>> allowed by all servers).
>>>>>>
>>>>>> Miguel, you just do not control what resource get created using RDF,
>>>>>> nor you control its interaction model...
>>>>>>
>>>>>> Alexandre
>>>>>>
>>>>>>>
>>>>>>> On Oct 9, 2014, at 3:14 PM, David Wood <david@3roundstones.com> wrote:
>>>>>>>
>>>>>>> On Oct 9, 2014, at 16:04, Miguel Aragón <miguel.aragon@base22.com> wrote:
>>>>>>>
>>>>>>> The approach that I’m offering allows applications to be moved from one
>>>>>>> service to another. The problems with relative URIs are these:
>>>>>>>
>>>>>>> If non empty, relative URIs (ex. <something>) are accepted, it doesn't make
>>>>>>> much sense to support the Slug header. What would happen if both of them
>>>>>>> were used?
>>>>>>>
>>>>>>> Example:
>>>>>>> Slug: something
>>>>>>> <somethingElse> a ldp:RDFSource.
>>>>>>>
>>>>>>> By allowing the client to send both null URIs and non empty, relative URIs,
>>>>>>> a weird behaviour would be expected:
>>>>>>>
>>>>>>> If a null URI was used. The base of the document needs to be: (parent’s URI)
>>>>>>> + (slug created)
>>>>>>> If a non empty, relative URI was specified. The base of the document needs
>>>>>>> to be: (parent’s URI) <- making sure that it ends in a “/"
>>>>>>>
>>>>>>> The logic needed for this behaviour will impose an unnecessary overhead for
>>>>>>> each request.
>>>>>>> As far as we know, specifying relative URIs and not defining a base URI
>>>>>>> results in an invalid RDF document.
>>>>>>> If the server supported the creation of multiple resources on a single
>>>>>>> request, null URIs will overlap with each other.
>>>>>>> Common parsers (like Jena) don't treat null URIs and relative URIs
>>>>>>> consistently.
>>>>>>>
>>>>>>>
>>>>>>> Hi Miguel,
>>>>>>>
>>>>>>> Thank you for clarifying your position.
>>>>>>>
>>>>>>> I think the thing that you are missing here is that the server always has
>>>>>>> the final say. It is up to the server to decide what to do with a Slug or
>>>>>>> when a base URI is missing. It might reject the request, use what it has or
>>>>>>> something else. This is in accordance with Web Architecture.
>>>>>>>
>>>>>>> For example, this issue report records what we (Callimachus Project) decided
>>>>>>> to do:
>>>>>>> https://github.com/3-Round-Stones/callimachus/issues/163
>>>>>>>
>>>>>>> Still, if LDP wants to specify this more tightly to assist interoperability,
>>>>>>> it will need to be careful. Deciding quickly could break a lot of services
>>>>>>> that are close to LDP compliance now.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Dave
>>>>>>> --
>>>>>>> http://about.me/david_wood
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Oct 9, 2014, at 2:58 PM, David Wood <david@3roundstones.com> wrote:
>>>>>>>
>>>>>>> On Oct 9, 2014, at 15:51, Miguel Aragón <miguel.aragon@base22.com> wrote:
>>>>>>>
>>>>>>> You say you like them, but you haven’t addressed the problems that I
>>>>>>> described. I’m not saying they should be prohibited, I’m saying it shouldn’t
>>>>>>> be mandatory to support them.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Hi Miguel,
>>>>>>>
>>>>>>> I honestly don’t see the problem you say you outlined and I did in fact give
>>>>>>> you a use case since you said you don’t have one. Relative resolution of
>>>>>>> URIs to the base allows portability in both data and applications built on
>>>>>>> that data.
>>>>>>>
>>>>>>> Why is it difficult to support the generation of a URI based on the
>>>>>>> concatenation of a base URI and a relative URI? I am not trying to be
>>>>>>> difficult, I just don’t understand why that is hard.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Dave
>>>>>>> --
>>>>>>> http://about.me/david_wood
>>>>>>>
>>>>>>>
>>>>>>> On Oct 9, 2014, at 2:43 PM, Andrei Sambra <andrei@w3.org> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 10/09/2014 03:42 PM, David Wood wrote:
>>>>>>>
>>>>>>> On Oct 9, 2014, at 15:11, Steve Speicher <sspeiche@gmail.com> wrote:
>>>>>>>
>>>>>>> On Thu, Oct 9, 2014 at 3:05 PM, Miguel Aragón <miguel.aragon@base22.com>
>>>>>>> wrote:
>>>>>>> Hi Nandana, thanks for responding.
>>>>>>>
>>>>>>> Null URIs are actually very problematic, and (not null) relative URIs just
>>>>>>> make the problem worse. With the approach that we have: Generic Request
>>>>>>> URIs, hash URIs can be used in the same way:
>>>>>>>
>>>>>>> Method: POST
>>>>>>> URL: http://example.org/container/
>>>>>>> Slug: miguel
>>>>>>> Body:
>>>>>>> @base <http://example.org/generic-requests/123123123123>.
>>>>>>> <> a foaf:PersonalProfileDocument;
>>>>>>> foaf:primaryTopic <#me>.
>>>>>>>
>>>>>>> Is resolved to
>>>>>>>
>>>>>>> <http://example.org/container/miguel> a foaf:PersonalProfileDocument;
>>>>>>> foaf:primaryTopic <http://example.org/container/miguel#me>.
>>>>>>>
>>>>>>> I honestly don’t see the case for using relative URIs (null or not null) at
>>>>>>> all. They bring many problems to the server and make the request document an
>>>>>>> invalid RDF document.
>>>>>>>
>>>>>>> I believe this is a general misconception, the base URI to use for
>>>>>>> resolution just instead carried outside the entity body.  Many RDF libraries
>>>>>>> allow you to supply the absolute base URI to use for resolution when handing
>>>>>>> off the model, this topic was discussed on the list some time ago [1].
>>>>>>>
>>>>>>> Since it is a common stumbling block and not that clear, I would suggest we
>>>>>>> include additional guidance in the best practices and guidance document [2].
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> For what it is worth, we just love relative URIs. This is because they allow
>>>>>>> us to easy move applications from one service to another. We would be quite
>>>>>>> unhappy if we could not both use relative URIs and be LDP compliant.
>>>>>>>
>>>>>>>
>>>>>>> +1
>>>>>>>
>>>>>>> Relative URIs are incredibly useful.
>>>>>>>
>>>>>>> -- Andrei
>>>>>>>
>>>>>>>
>>>>>>> Regards,
>>>>>>> Dave
>>>>>>> --
>>>>>>> http://about.me/david_wood
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> - Steve
>>>>>>>
>>>>>>> [1]: http://lists.w3.org/Archives/Public/public-ldp-wg/2014Apr/0008.html
>>>>>>> [2]:
>>>>>>> https://dvcs.w3.org/hg/ldpwg/raw-file/default/ldp-bp/ldp-bp.html#use-relative-uris
>>>>>>>
>>>>>>>
>>>>>>> On Oct 9, 2014, at 1:55 PM, Nandana Mihindukulasooriya <nmihindu@fi.upm.es>
>>>>>>> wrote:
>>>>>>>
>>>>>>> Hi Miguel,
>>>>>>>
>>>>>>> I guess the most common use case for the (not null) relative URIs is usage
>>>>>>> of hash URIs. For example, something like this.
>>>>>>>
>>>>>>> <> a foaf:PersonalProfileDocument;
>>>>>>> foaf:primaryTopic <#me> .
>>>>>>>
>>>>>>> I think this case is less problematic because typically the profile document
>>>>>>> <> will become something like  <http://ex.org/container/miguel> and the
>>>>>>> <#me> becomes <http://ex.org/container/miguel#me>.
>>>>>>>
>>>>>>> But if you have something like
>>>>>>>
>>>>>>> <> a foaf:PersonalProfileDocument;
>>>>>>> ex:property <anotherResource> .
>>>>>>>
>>>>>>> This is a bit problematic because the resolution of it is a bit dependent of
>>>>>>> ending slash. The above snippet resolved against the base
>>>>>>> <http://ex.org/container/miguel> will become
>>>>>>>
>>>>>>> (a) <http://ex.org/container/miguel> a foaf:PersonalProfileDocument;
>>>>>>> ex:property <http://ex.org/container/anotherResource> .
>>>>>>>
>>>>>>> and the same is resolved against the base <http://ex.org/container/miguel/>
>>>>>>> will become
>>>>>>>
>>>>>>> (b) <http://ex.org/container/miguel/> a foaf:PersonalProfileDocument;
>>>>>>> ex:property <http://ex.org/container/miguel/anotherResource> .
>>>>>>>
>>>>>>> However, I think LDP clients should never use the (a) with the slug to refer
>>>>>>> to itself because it can always use the null URI to refer to itself. We also
>>>>>>> discourage the use of dot segment relative URIs in the LDP BP. I wonder what
>>>>>>> are practical usages of non-hash relative URIs in POSTed content (before
>>>>>>> creation when the base of the document is unknown still).
>>>>>>>
>>>>>>> Best Regards,
>>>>>>> Nandana
>>>>>>>
>>>>>>> On Thu, Oct 9, 2014 at 6:25 PM, Miguel Aragon <miguel.aragon@base22.com>
>>>>>>> wrote:
>>>>>>> Hello to everyone
>>>>>>> Based on the design and implementation process that my team and I have
>>>>>>> experience, I've several comments about the LDP Spec that I'd like to share
>>>>>>> with you. But first lets make sure that we talk in the same language:
>>>>>>>
>>>>>>> Concepts
>>>>>>> Note: Keep in mind that these are the concepts that are working for us. By
>>>>>>> no means I'm criticising the "Academic point of view"
>>>>>>> Relative URI: A relative URI that was not resolved to an absolute URI
>>>>>>> because the document didn't specified a base URI (@base).
>>>>>>> Null URI: an empty, relative URI.
>>>>>>>
>>>>>>> Creation of LDP RDF Sources (LDPRS)
>>>>>>> There are several key points in section 5.1 Introduction that need to be
>>>>>>> considered:
>>>>>>> An LDPRS can be created by issuing a POST to an LDPC.
>>>>>>> The client can specify a Slug header to provide a hint of the URI desired
>>>>>>> for the new resource.
>>>>>>> The examples show that a null URI can be used for the resource to be
>>>>>>> created. The resulting URI will be forged by the server.
>>>>>>> The LDP test suite goes beyond this and uses relative URIs in the resources
>>>>>>> that are POSTed to the server. (ex. <something> a ldp:RDFSource. ).
>>>>>>> At first we followed this approach, but when we started using JSON-LD as our
>>>>>>> main RDF format, we started encountering several problems with it:
>>>>>>> If non empty, relative URIs (ex. <something>) are accepted, it doesn't make
>>>>>>> much sense to support the Slug header. What would happen if both of them
>>>>>>> were used?
>>>>>>>
>>>>>>> Example:
>>>>>>> Slug: something
>>>>>>> <somethingElse> a ldp:RDFSource.
>>>>>>>
>>>>>>> By allowing the client to send both null URIs and non empty, relative URIs,
>>>>>>> a weird behaviour would be expected:
>>>>>>> If a null URI was used, forge a slug for the new resource and take the LDPC
>>>>>>> URI as a base for the URI of the resource to be created.
>>>>>>> If a non empty, relative URI was specified, treat that as a hint for the
>>>>>>> desired slug and use the LDPC URI as a base for the URI of the resource to
>>>>>>> be created.
>>>>>>> The logic needed for this behaviour will impose an unnecessary overhead for
>>>>>>> each request.
>>>>>>> As far as we know, specifying relative URIs and not defining a base URI
>>>>>>> results in an invalid RDF document.
>>>>>>> If the server supported the creation of multiple resources on a single
>>>>>>> request, null URIs will overlap with each other.
>>>>>>> Common parsers (like Jena) don't treat null URIs and relative URIs
>>>>>>> consistently.
>>>>>>> Some of the possible approaches for addressing these problems are:
>>>>>>> The obvious solution would be to use fully qualified URIs on every request.
>>>>>>> But the client doesn't always know what the resulting URI will be.
>>>>>>> Another approach would be to use a placeholder, a fully qualified URI that
>>>>>>> the server knows it's acting just as a placeholder (Ex.
>>>>>>> <http://example.org/placeholder>). But that would mean the client is
>>>>>>> constantly specifying new triples for the same resource (in an academic
>>>>>>> point of view). And the problem of multiple resources on a single request
>>>>>>> wouldn't be solved by this approach.
>>>>>>> After some thought, we came with the concept of "Generic Request URI".
>>>>>>>
>>>>>>> Generic Request URI
>>>>>>> A URI that has as a base, a known and never changing URI, and that ends with
>>>>>>> a slug that is different for every Generic Request URI created (in our case
>>>>>>> a timestamp).
>>>>>>> Example
>>>>>>> A template of the form: http://example.org/generic-requests/<timestamp>
>>>>>>> would create URIs like:
>>>>>>> <http://example.org/generic-requests/1412868212000>
>>>>>>> <http://example.org/generic-requests/1412868258000>
>>>>>>> <http://example.org/generic-requests/1412868262000>
>>>>>>> Using a Generic Request URI when creating resources covers the following
>>>>>>> problems:
>>>>>>> It standardises the URIs the server will receive.
>>>>>>> If the client wants to specify a hint, it would do so by passing a Slug
>>>>>>> header.
>>>>>>> Each request describes a unique resource and thus it is academically
>>>>>>> correct.
>>>>>>> Multiple resources can be created by declaring each one with a different
>>>>>>> Generic Request URI.
>>>>>>>
>>>>>>>
>>>>>>> So an LDP server would accept requests with the following forms:
>>>>>>> A resource with a fully qualified URI. In this case the client attempts to
>>>>>>> create a resource with a known URI so a Slug header isn't allowed and if the
>>>>>>> URI is already in use the server would respond with 409 Conflict.
>>>>>>> A resource with a Generic Request URI and no slug specified. The server
>>>>>>> would use the URI of the parent resource as a base and forge a slug for the
>>>>>>> new resource however the server is configured to do so.
>>>>>>> A resource with a Generic Request URI and a Slug header. The server would
>>>>>>> use the Slug header as a hint for the URI of the new resource to be created.
>>>>>>> I've more comments and concepts to share, but I will write another email for
>>>>>>> them.
>>>>>>>
>>>>>>> --
>>>>>>> Miguel Aragón
>>>>>>> Mobile: +52 (811) 798 9357
>>>>>>> Skype: miguel.araco
>>>>>>> Email: miguel.aragon@base22.com
>>>>>>> CONFIDENTIALITY NOTICE: This e-mail message, including any attachments, is
>>>>>>> for the sole use of the intended recipient(s) and may contain confidential
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>
>>>
>

Received on Thursday, 9 October 2014 20:40:01 UTC