[occi-wg] Categories and Collections

Ralf Nyren ralf at nyren.net
Mon Oct 4 10:41:32 CDT 2010

Nice work Andy!

A few comments:

- Could we have some HTTP-rendering examples of how to add/remove Kind  
instances to/from a collection other than the defining collection?

- The section on Navigation refer to Links and Actions, is this the Core  
base types referred to? The Core Link type has little to do with paging  
 from my point of view. The Link Header in HTTP on the other hand can be  
used for _both_ representing Core Links and paging. I see how Core Actions  
can be used to express paging but the way Actions are rendered in HTTP  
using Link Headers has again little to do with the Link base type. Please  
see "Actions and the Link Header" at the end of [1] for a full description  
of this terminology confusion.

- When the http://schemas.ogf.org/occi/core# was introduced I thought it a  
good idea to have it reserved for Categories defining the OCCI base types  
(i.e. Resource, Link, Action). Although not necessary I think keeping this  
distinction make the spec a bit easier to understand. The current  
definition of Categories is:

The Category type represent the classification mechanism used by OCCI. It  
MUST be implemented. From a system point of view a Category is used for  
two different classification purposes. See also section 4.3 "Type System".

1. Taxonomy. A Category is used to assign static type information to each  
resource type inheriting Kind or a descendant of Kind. This use of  
Categories denotes the OCCI "static type system". A unique Category MUST  
be assigned to every descendant of Kind. See the section  
2. Folksonomy. A Category can be used to assign tags to resource instances  
via a mix-in like model. A Category mix-in MUST NOT be related to an OCCI  
base type (or any descendent of Kind) and MUST NOT be the unique  
identifier thereof. Example use cases are collections, location  
information and templates for virtual machine provisioning.

Collections play nicely with 2, the "folksonomy" use of Categories. My  
point is that maybe we should have different schemes for Category use case  
1 and 2, that is for Categories defined in Core. What do you think? It is  
not terribly important though.
I.e. use a different scheme for the "tag" Category.

I will annotate the wiki page as well.

regards, Ralf

[1] http://forge.ogf.org/sf/wiki/do/viewPage/projects.occi-wg/wiki/Link

On Sun, 03 Oct 2010 17:16:57 +0200, Andy Edmonds <andy at edmonds.be> wrote:

> Hey all,
> I've placed a write up of how categories and collections related to each
> other. Also there is how one can interact with collections. I've tried to
> keep the description as non-rendering-specific as possible.
> http://forge.ogf.org/sf/wiki/do/viewPage/projects.occi-wg/wiki/Collections
> If there are comments etc please annotate the wiki page at the  
> appropriate
> place or place your questions in the "Open Issues" section.
> Andy
> andy.edmonds.be

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