Two types of inputs were specified to allow authors to define the inputs
that are absolutely required in order to execute the task (i.e. mandatory)
versus those that may provide some useful additional information but the
lack thereof does not prevent one from completing the task. This was not
done for outputs as those listed were considered the primary focus of the
task and what was being produced and if one was not produced it would not
necessarily break the task. Typically those artifacts which may be
updated as a "side affect" of performing the task are not listed as this
would lead to an extensively long list of outputs which would be very
similar across many tasks. It is often preferable to identify those types
of changes in an update task for that work product with the inputs to that
task being the changed elements most likely to trigger the need for such
an update.