Using substitution filters, a service template is a valid candidate to substitute an abstract node template if the following two conditions are met:

1. The type advertised in the substitution_mappings section of the service template matches the type of the abstract node template.

2. The property values of the abstract node template satisfy the constraints defined in the substitution_filtter of the substituting service template.

Motivation:

When multiple matching templates are available, the orchestrator must provide mechanisms to allow the end-user to drive the decision about which matching template must be selected.

Tosca simple YAML profile allows for substitution_filter to be specified for a topology template to provide processing instructions to the orchestrator.

TOSCA uses a substitution_filter in the substitution mappings section of a service template to further constrain the abstract nodes for which a service template can be a valid substitution.