SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
COMMUNITY
F.MASONS
L.MASONS
N.MASONS
F.BOY.SCOUTS
L.BOY.SCOUTS
N.BOY.SCOUTS
Figure 4-3. Automatically-defined Attributes of COMMUNITY Entities
The attributes starting with F. are set pointers that point to the first member of the respective sets.
The attributes starting with L. are set pointers that point to the last member of the respective sets.
The set members, as we shall see, point to one another, defining their interrelationships and making
the connection between the set owner and the set members complete. The attributes starting with
N. maintain the number of entities in each set.
The second statement declares that each entity of the class MAN may belong to sets called MASONS
and BOY.SCOUTS. It is important to note that membership is declared as possible in this statement,
but not mandatory. This statement automatically defines the set attributes shown in figure 4-4 for
member entities.
MAN
P.MASONS
S.MASONS
M.MASONS
P.BOY.SCOUTS
S.BOY.SCOUTS
M.BOY.SCOUTS
Figure 4-4. Automatically-defined Attributes for Members of the Class MAN
The attributes starting with P. are set pointers pointing to the predecessor entity in the indicated set.
Those starting with S. are set pointers pointing to the successor entity in the indicated set, and those
starting with M. indicate whether an entity is currently a member of the set. The concepts of predecessor
and successor, as well as first and last, can be best explained by an illustration. In figure
4-5 the entity COMMUNITY owns one set called MASONS. The members of the set are entities of the
class MAN. The entity-set relationships are defined by the statements:
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