SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
It is, of course, possible to have more than one process or event of the same kind scheduled to occur
at the same or different times in the future. For example, a machine-shop simulation may have
many indentical machining activities in progress concurrently. Completion of two or more of these
may be scheduled to occur at exactly the same time. If this happens, the timing routine uses a “first
scheduled-first occurs” rule to “break the tie.” The order in which simultaneous events of equal priority
are executed is determined by the sequence in which they were previously scheduled. Although
several events can appear to take place at the same instant in simulated time (the simulation
clock has the same value during the execution of each), there are often good reasons for wanting to
impose a priority ordering. This may be done by specifying the break ties statement:
or
break process/event name ties by high attribute name
break process/event name ties by low attribute name
which gives priority to the process with the high (low) attribute value when two or more propcess
notices of the same type have the same process time. The attributes are, of course, ones that have
been defined in every statements for the process named. In cases where more than one set of tiebreaking
attributes are needed, clauses of the form:
or
, then by high attribute name
, then by low attibute name
can be added to the break ties statement. As many such clauses may be added as are necessary.
Processes defined by the statements:
process
every DISPATCH has a VALUE, a DUE.DATE and a PRIORITY
might have ties resolved among competing process notices by statements such as:
1. break DISPATCH ties by high PRIORITY
2. break DISPATCH ties by high PRIORITY, then by low DUE.DATE
3. break DISPATCH ties by high VALUE, then by LOW PRIORITY,
then by high DUE.DATE
In statement 1, among DISPATCH processes scheduled to occur at the same simulated time, the process
notice with the largest PRIORITY attribute will occur first. In 2, among process notices scheduled
to occur at the same simulated time and having identical PRIORITY values, the notice with the
smallest DUE.DATE will occur first; and similarly for 3 and other variations.
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