Re: Comments on the LDP Spec: Creating new Resources

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
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>
>

Received on Thursday, 9 October 2014 20:34:22 UTC