SIMSCRIPT II.5 Programming Language

Discrete Simulation Concepts
ized, they must compete with the externally triggered event notices on a first-come, first-served
basis.
Since an event or process routine can be activated in either of two ways, and each of these ways
provides a different source of data for the routine, a logical expression is provided for use within
such a routine to determine how this instance of the routine was initiated. The expression compares
the keyword process or event with either of the property words internal or external and
yields a true or false result. The form of the expression is:
and
process is propertyorprocess is not property
event is propertyorevent is not property
as in the statements:
and
if process is internal,
read NAME and DESTINATION as B 20, (2) I 10
always
if event is external and data is ended,
stop
otherwise
5.3.9 Triggering Processes and Events Externally
Events are triggered externally by event data records appearing in chronological order on each of
the external input devices. Such a data record contains the name of an event or process, the time at
which it is to occur, and, optionally, data to be read by the event or process routine. The event data
records are read one at a time, their information recognized and deciphered, and event or process
notices created for the events or processes indicated. This paragraph deals with two issues: the operations
performed by SIMSCRIPT II.5 when external process records are read and the format of
the external data records.
When a start simulation statement is recognized, the first task performed by the timing mechanism
is to read information about the first event on each of the external units. When an external
data record is read, the event class is recognized and the event time computed from data on the record.
An event or process notice is created, and the scheduled event time and the number of the unit from
which the data record was read are stored in the time.a and eunit.a attributes of the notice. If
the event notice has been declared with user-defined attributes, it conforms to the preamble declaration.
However, none of the user-defined attributes is assigned values. The notice is then filed in
the future events set corresponding to its class. Internally and externally generated notices are filed
together. They are distinguished by the eunit.a attribute. A coded value of eunit.a, usually
zero, denotes that a notice has been internally scheduled.
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