[occi-wg] JSON Rendering

[Ralf Nyren]

On Tue, 03 Apr 2012 14:31:24 +0200, Feldhaus, Florian  
<florian.feldhaus at gwdg.de> wrote:

> Hi,
>
> once again I would like to reiterate the JSON rendering. First a short  
> overview what Alexander and I think are the main points we should  
> address:
> - remove all HTTP Rendering specific parts from the JSON rendering

Remember that an OCCI rendering (as currently specified) includes _both_  
protocol and data format at the moment.

I like the idea of having a common HTTP Protocol rendering spec which the  
JSON rendering could be built upon though.

However, the current HTTP rendering doc lacks things like e.g. request  
parameters in URL which I would say is necessary to have a sane JSON  
rendering.

Updating the HTTP rendering doc to have a clear separation between  
protocol and data format would address this of course.

> - make the JSON rendering slim and remove everything which is not a  
> representation of the OCCI model

You mean the pagination links etc? Or something else as well?

> - consider using RFC 5988 "Web Linking" for collection information (e.g.  
> index, next, previous,…)

Gary and I had an email conversation which resulted in a solution where  
all info necessary for pagination would end up in the request URL. I.e.  
basically eliminating the need for using special headers (such as RFC  
5988).

The request parameters to a collection simply allow you to specify the  
amount of resource instances you want returned either _before_ or _after_  
a specific occi.core.id.

> Examples:
> http://pastebin.com/ZK9Uf0K1 (Entities)

Nice, I like that you keep the "attributes" hash now ;)

How do you render Link attributes for the links tied to an OCCI Resource?

> To keep the mail short, a detailed discussion can be found in the  
> attached text document.

Just picking out one thread:

> resources and links should be represented differently. The entry "links"  
> is unique for resources and the entries "target" and "source" are unique  
> for links.

Sounds goods. So the top-level hash of the collection format would have  
one hash "resources" and another hash "links" then?
I mean, we still have to cover the case where the client asks for  
"everything" at the top-level URL and thus gets both Resources and Links  
in the response.

> In OCCI Core the attribute names should be changed from occi.core.source  
> and occi.core.target to just source and target, as both are representing  
> connections to other resources from within the OCCI model (similar to  
> links in resources, or kind in entity).

occi.core.source and occi.core.target was named simply source/target up  
until just before the OCCI HTTP Rendering doc was published.

The fundamental problem here is that we have two different sorts of  
"attributes".
  1. Attributes as part of the OCCI Core model. These include both  
Entity.id, Entity.title, Resource.summary, Resource.links, Link.target,  
Link.source, etc
  2. Attributes as exposed by an OCCI rendering. The HTTP Rendering exposes  
id, title, summary as attributes as well as target and source. However the  
Resource.links attribute is not exposed as an attribute...

There is no clear distinction here which IMO leads to confusion.

Also remember that a subclass of OCCI Link may have Link.target pointing  
at some arbitrary external object.

regards, Ralf