SIMSCRIPT II.5 Programming Language

Modelling Concepts
define entity name as an integer variable
4.6 System Attributes
To provide consistency in usage, it is convenient to be able to declare attributes as belonging to the
system, rather than to a particular entity. These attributes appear much like global variables, but
with some differences. Attributes of the system are declared by statements of the form:
the system has attribute name list
For most purposes, the statements:
and:
the system has an X and a Y
define X and Y as variables
are equivalent. Because there is only one "system," references to system attributes are not indexed
or subscripted, as are references to attributes of permanent and temporary entities. A value of 1 is
assigned to the variable X by the statement let X = 1, whether X is defined as in the first or second
example above. System attributes will be subscripted if the background dimensionality condition
at the time of their declaration is greater than zero. X is declared to be a two-dimensional system
attribute by the statements:
normally, dimension is 2
the system has an X
The convenience of system attributes derives mainly from their use as pointers that enable a program
as a whole to own sets. The statement:
the system owns a QUEUE
specifies that a program contains two system attributes named F.QUEUE and L.QUEUE that point to
the first and last entities belonging to a set named QUEUE. Several system-owned sets can be defined
at one time by the statement:
the system owns set name list
If a background dimensionality, other than zero, is declared, the effect is to define any system-defined
attributes, including any set pointers, as arrays rather than as unsubscripted variables, as in:
normally dimension is 2
the system owns a TABLE and has a MATRIX
Subscripted system attributes, both explicitly declared and any implicitly defined set pointers, must
be reserved before they can be used. To use the system set TABLE and the system array MATRIX,
defined above, a statement such as:
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