| This is based on an example in the draft paper ''PSL: A Semantic Domain for Flow Models''  July 7, 2003,
| by CONRAD BOCK National Institute of Standards conrad.bock@nist.gov
| and  MICHAEL GRUNINGER  michael.gruninger@nist.gov
|
| The food service process must include ordering, preparing, serving, eating, and paying,
| but not necessarily in exactly that order. The constraints might be:
|  * Ordering, preparing, and serving always happen before eating.
|  * Serving happens after preparing and ordering.
|  * Paying can happen anytime in the process.
|
|  The rule for sequencing the activities is a simplified one for the purposes of this example.



this-activity1 must occur before this-activity2
===============================================
ordering                        eating
preparing                       eating
serving                         eating
preparing                       serving
ordering                        serving


in scenario this-number step this-step is this-activity
=======================================================
              1               1            ordering
              1               2            paying
              1               3            eating


we can start with some-activity
-------------------------------------
in scenario 2 step 1 is that-activity


in scenario 2 step some-step is some-activity
that-activity must occur before some-activity2
not : there is an activity that must occur between that-activity and that-activity2
that-step + 1 = some-step2
------------------------------------------------------------------------------------
in scenario 2 step that-step2 is that-activity2


some-activity1 must occur before some-activity2
that-activity2 must occur before some-activity3
--------------------------------------------------------------------------
that-activity1 followed by that-activity2 must occur before that-activity3


some-activity1 followed by some-activity2 must occur before some-activity3
------------------------------------------------------------------------------
there is an activity that must occur between that-activity1 and that-activity3


some-activity is being modeled
not : that-activity has a precondition
--------------------------------------
we can start with that-activity


some-activity1 must occur before some-activity2
-----------------------------------------------
that-activity2 has a precondition


in scenario some-number step some-step1 is some-activity1
in scenario that-number step some-step2 is some-activity2
that-step1 is less than that-step2
-------------------------------------------------------------------
in scenario that-number that-activity1 occurs before that-activity2


in scenario some-number step some-step2 is some-activity2
some-activity1 must occur before that-activity2
not : in scenario that-number that-activity1 occurs before that-activity2
----------------------------------------------------------------------------------------------
in scenario that-number step that-activity1 should have happened before that-activity2 but did not


some-activity1 must occur before some-activity2
that-activity2 must occur before some-activity3
-----------------------------------------------
that-activity1 must occur before that-activity3


some-activity1 must occur before some-activity2
-----------------------------------------------
that-activity1 is being modeled


some-activity1 must occur before some-activity2
-----------------------------------------------
that-activity2 is being modeled


this-activity is being modeled
==============================
paying