http://lists.oasis-open.org/archives/sca-policy-comment/200906/msg00006.html

Bullet 4 in section 4.12.1 says that to calculate the required intent
set for an element "add any intents found in the @requires attributes of
each ancestor element in the element's structural hierarchy." This
means, for example that any intents attached to a component apply to all
its services and references. Thus, if 'confidentiality' specified at
the component level, 'confidentiality' applies to all its services and
references.

But this may not be what is always desired. A shopping site may wants
all its ordering and billing messages encrypted but there may not be any
need to encrypt its search messages. Of course, the confidentiality
intent can be applied to individual services/references to cover this
usecase but we may also want to add the ability to control inheritance.
For example at the higher level we may want to say "this applies to all
descendants except ...." or on an element we may want to say "this
element does not inherit from its ancestors ".