Random sourceAttributeID Question

[Klingenstein, Nate]

Why is sourceAttributeID declared in the AttributeDefinition rather than in the dependencies themselves?  Wouldn't it make more sense the other way around?

"This defines the name of an IdPAttribute used as input to the attribute definition, and applies only to some definition types.

The source attribute may be the output of another attribute definition or the output of a DataConnector. If any data conectors are used as dependencies, the source attribute MUST be identified or an error will result."

https://wiki.shibboleth.net/confluence/display/IDP30/SimpleAttributeDefinition
https://wiki.shibboleth.net/confluence/display/IDP30/AttributeDefinitionConfiguration#AttributeDefinitionConfiguration-CommonAttributes