[OASIS Issue Tracker] (TOSCA-186) DEFER - model composition (Nested templates)

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    [ https://issues.oasis-open.org/browse/TOSCA-186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=51246#comment-51246 ] 

Chris Lauwers commented on TOSCA-186:
-------------------------------------

Yes, if you're postulating a requirement for substitutability (your R3), then that requirement can only be satisfied by adding support for substitution :-)

I wonder if that is really what is needed, however. At the core, what TOSCA is trying to do is to create application topologies by matching capabilities to requirements. The "nesting" discussion, in my opinion, is all about finding ways to satisfy requirements with a complex topology rather than with a single node. If that's the real goal, then let's re-use the existing paradigms of "node templates" and associated "capabilities", and let's allow for node templates that represent complex topologies by allowing composition. It seems that's what you're arguing for anyway. You make the statement that "... The way to implement this would be via some kind of proxy node template instance that provides the abstract view, which is backed by the nested topology". That's exactly what I'm proposing, except that i'm trying to make this "proxy node template" explicit rather than implicit, which would eliminate the need for all the new mechanism you're proposing. 


> DEFER - model composition (Nested templates)
> --------------------------------------------
>
>                 Key: TOSCA-186
>                 URL: https://issues.oasis-open.org/browse/TOSCA-186
>             Project: OASIS Topology and Orchestration Specification for Cloud Applications (TOSCA) TC
>          Issue Type: Improvement
>          Components: Profile-YAML, Spec - Simple Profile
>            Reporter: Shitao Li
>            Assignee: Thomas Spatzier 
>
> In TOSCA 1.0, it defined the composition of service templates(clause 3.5), which allow a service template to be used as a node template in another service template. 
> In many cases, this is very important and useful feature, especially when describe the complicated service.
> However, in TOSCA-simple-profile-YAML, it seems that this feature does not support.



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