Re: Comments on the LDP Spec: Creating new Resources

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).

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

Received on Thursday, 9 October 2014 20:33:31 UTC