[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=52240#comment-52240 ] 

Thomas Spatzier  commented on TOSCA-186:
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I don't think that using nested node_templates inside a node_template will make things easier. In at least 90% of the use cases, as I would guess, service templates will be used for deploying applications (or workloads in general). And in those majority of cases calling the "thing" a node_template with nested node_templates would be confusing. It is really a topology_template that describes the topology of the application in terms of node templates and relations.
In the same way, inputs and outputs is more intuitive in those majority of use cases.
Also, typing a topology template is not necessary in the majority of use cases, so I really don't see a need for re-using the node_template concept. Only IF a topology template is to substitute a node template, adding the necessary substitution information would be an acceptable additional annotation.

All that said, I think it makes sense to keep different names for different concepts. I don't think our goal should be to keep the number of keywords in TOSCA to a minimum. That will add more if-then-else cases depending on the context in which things are used, also implementation will become more complicated.

Finally, get_attribute does not have to become more complicated if we stick to a clean encapsulation model.

> 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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