[occi-wg] Query uniqueness

[Andre Merzky]

On Mon, Apr 11, 2011 at 6:21 PM, Ralf Nyren <ralf at nyren.net> wrote:
>
> The only rule is that two Categories cannot map to the same location. So you
> cannot have two different Categories mapping to e.g. /compute/.
>
> This means that with user-defined Mixins an OCCI service must refuse to
> create a Mixin for which the specified location path already is taken.

which basically means that you need a registry of valid mixins?

A.



> /Ralf
>
> On Sun, 10 Apr 2011 14:34:12 -0600, Gary Mazz <garymazzaferro at gmail.com>
> wrote:
>
> Ok,
> In this example:
>
> Retrieving All Resource Instances Belonging to Mixin or Kind The HTTP verb
> GET must be used to
> retrieve all resource instances. The service provider MUST return a listing
> containing all resource
> instances which belong to the requested Mixin or Kind:
>> GET /compute/ HTTP/1.1
>> [...]
> < HTTP/1.1 200 OK
> < [...]
> <
> < X-OCCI-Location: http://example.com/vms/user1/vm1
> < X-OCCI-Location: http://example.com/vms/user1/vm2
> < X-OCCI-Location: http://example.com/vms/user2/vm1
>
> An OCCI implementation MUST support a filtering mechanism. If a HTTP
> Category is provided in the
> request the server MUST only return the resource instances belonging to the
> provided Kind or Mixin.
> The provided HTTP category definition SHOULD be different from the Kind or
> Mixin definition which
> defined the location path used in the request.
>
> If an OCCI Entity attribute (X-OCCI-Attribute) is provided in the request
> the server MUST only return
> the resource instances which have a matching attribute value.
>
> We see the the URI path '/compute/'. This name space confusion comes into
> the picture.. Is the URI path, indicating the 'location' specified by a
> category or is it the 'term' of the category? If it is the "location" there
> is the possibility of returning back multiple categories if the 'location'
> attribute is the same across multiple categories.  If it is the "term",
> there can be resources based on categories using the same 'term' but using
> differnt schemes.
>
> -gary
>
>
>
> On 4/10/2011 12:59 PM, Ralf Nyren wrote:
>
> please see below:
>
> On Sun, 10 Apr 2011 19:08:44 +0200, Gary Mazz wrote:
>
> Maybe I'm looking that the specifications too long, but it seems you can
> place more than one term in a query named space... for example, a query
> named space '/network/'  could refer to both the occi scheme and a
> private scheme.
>
> The namespace for different Category/Kind/Mixin instances is defined by the
> scheme, e.g. http://schemas.ogf.org/occi/core#. In this case we talk about
> the namespace for different types, i.e. Entity, Resource, Link, Compute,
> Storage, etc.
>
> We also talk about the namespace used for Entity IDs, i.e. the IDs of
> resource instances in a system. In the case of the HTTP Rendering this
> namespace is mapped to the URL namespace of HTTP.
>
> To further complicate things we have a mechanism of hooking a Kind/Mixin
> instances into this HTTP URL namespace by use of the "location" parameter.
> As you know a Kind or Mixin instance represents a collection of all resource
> instances (Entity sub-type instances) associated with the Kind or Mixin.
> This collection can be retrieved by querying the "location" URL.
>
> So to answer your question on the mapping of e.g. the "/network/" HTTP path
> it depends if you have a Kind/Mixin hooked into that path or not. If there
> is such a hook (i.e. you have a Category: ... location=/network/ somewhere
> in the query interface) you will find the collection of the Kind/Mixin.
> However if you do not have a Kind/Mixin location mapped at /network/ you
> must follow the rules in section 3.4.2 "Operation on Paths in the
> Name-space".
>
> hmm... makes sense? :P
>
> There is no requirement that identical 'terms' used to describe a
> resource category to have a similar or the same functional
> characteristics as terms defined in the occi scheme.
>
> You are free to define e.g. Category: compute;
> scheme=http://provider.com/blah#  which is represents a coffee machine. It
> might be slightly misleading but as long as you use your own scheme
> namespace you can essentially do whatever you want.
>
> There is a mention of an "entity_type" to "Entity type uniquely
> identi%0Cfied by the Kind instance." However it doesn't say "entity_type"
> uniquely "identifies" the Kind Instance. The only way to uniquely
> identify a Kind is by scheme:term.  And this leads back to the issue
> with the query
>
> The Kind.entity_type is intended to contain a reference to the type (a class
> in most OO langs) which is identified by the Kind. Example (python-ish):
>
> # Compute is a class which inherits Resource which inherits Entity.
>
> # Thus is the Kind instance which identifies the Compute type (class)
> defined:
> compute_kind = Kind()
> compute_kind.term = "compute"
> compute_kind.scheme = "http://schemas.ogf.org/occi/core#"
> compute_kind.entity_type = Compute
>
> # If you want to create a new Compute instance you could do:
> class_ref = compute_kind.entity_type
> my_compute = class_ref()
>
> So Kind.entity_type is a reference to the type which the Kind instance
> identifies. This is of course not applicable to all programming languages
> but the idea is that given an instance of Kind you should be able to find
> out the Entity type it identifies.
>
> /Ralf
>
>
>
>
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>
>



-- 
So much time, so little to do...
[Garfield]