Re: Comments on the LDP Spec: Creating new Resources

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 20:21:31 UTC