[occi-wg] Link & Linking

[Ralf Nyren]

I studied your document on Link & Linking [1]. Nice write-up!

When a Link is turned into a resource and thus exposed to CRUD semantics  
it will only be valid in the response to a GET request of an associated  
Resource, right? That is, using POST/GET/PUT/DELETE with e.g. a compute  
resource any Link headers will only be present in the GET response?

If so we solve the problems of updating and removing links although we  
still have the the side effects when deleting a resource with associated  
links. I.e. that the DELETE operation of a resource should remove any  
associated links to avoid dangling links.

Another problem with Link as a resource is that now there can be circular  
links and links pointing to other links.

I think a problem here is that you try to model the concept of  
bi-directional links on top of Web Links which are strictly unidirectional  
(correct my if I am wrong). When you do this an important question to ask  
is what OCCI really is. Is it an interface or is it a representation  
model? If we decide OCCI is limited to be an interface I say  
unidirectional links are all we need. It is not up to OCCI to represent  
the relation between resources for persistent storage, it should merely be  
able to _display_ links to other resources. It is not like an IaaS  
provider would use OCCI as its internal representation format.

Now, look at the analogy with web pages. A web page is a resource, that is  
easy to see and CRUD semantics apply as best they ever could. A web page  
may have links to other web pages, unidirectional links. Thus links will  
be removed when the resource is removed and referential integrity is not  
guaranteed. Why not apply the same model in OCCI? We leave the issue of  
referential integrity in the hands of the IaaS provider. If we create a  
compute resource with a link to a storage resource and then view the  
storage resource it is up to the provider to decide if a reverse link to  
the compute resource should be included in the response.

Sorry if this last part was a bit confusing. I will add a proposal of my  
own to the Link & Linking document so we have a basis for discussion.

regards, Ralf


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