[occi-wg] Link specification

[Csom Gyula]

[1] Yep I've caught it:) When first reading the drafts I missed the UML diagram Andy pointed at. 
Now the diagram clarifies the situation on source resources and some texts could further clarify
it as you pointed at. However I had/have still some question regarding target resources. 

Yesterday, I've got just a minor, documentation question regarding binary associations (see my 
previous emall for details). However after thinking more about the topic, I've found another one 
regarding the behaviour. Take the following example: 

The user creates a new compute using some networks and disks, ie. define links to some network 
and disk. The compute is then deployed and soon becomes up and running. Then later the user 
deletes some network and disk... well, maybe she forgets about that they are used within some 
running compute. According to the implicit delete behaviour the computes will "loose" its disks and 
networks which might mean that it becomes unusable. 

I think deleting source resources with links is a natural behaviour since links are in fact "owned" 
by the sources. However this might not be the case with target resources, hence alternatives 
might be examined as well - like:

* No delete - The system prevents from deleting a target resource with exisiting links pointing to it.

* Graceful delete - New resources cannot use the deleted target resource, but existing ones still can. 
That is the target resource will be "fully" deleted when all exising links pointing to it are deleted as well.

* Warning on delete - In such cases the system issues a warning before deleting the target 
resource which must be confirmed by the client. This is related to another topic, namely to 
reverse links [2].

* Force or immediate delete - The original behaviour where the system silently deletes the target 
resource and its associated links (pointing to it).

Gyula
________________________________________
Feladó: Ralf Nyren [ralf at nyren.net]
Küldve: 2010. szeptember 1. 22:38
Címzett: Csom Gyula; Edmonds, AndrewX; occi-wg at ogf.org
Tárgy: Re: [occi-wg] Link specification

On Wed, 01 Sep 2010 18:32:18 +0200, Csom Gyula <csom at interface.hu> wrote:

> [1] action on resource delete
> The working draft specifies the behaviour of deleting links (ie. "An
> OCCI server MUST NOT
> delete the associated Resources upon receiving a client DELETE request
> for a Link.").
>
> It's counter part should be also defined, ie. the behaviour of deletion
> of associated resources.
> Should the server automatically delete links, as well (CASCADE DELETE
> behaviour)? Or
> should it prevent from deleting a resource, if there's a link pointing
> to it? Or should it be
> configurable either per link instance or link type?

As Andy says this is already defined by the model definition in
Core&Models. We should add the necessary text to make this clear in
writing as well though.

> [3] built in link types
> The working draft enables subtyping links: "An OCCI server MAY enforce
> additional
> attributes at creation time if the link has been subtyped using
> additional categories."

Actually the Core & Models document already allow for Links to be
subtyped. The above statement says that a server is allowed to refuse a
Link from being created if some attribute of the subtype is not present.
In other words, a Link subtype can have mandatory attributes.

regards, Ralf