SIMSCRIPT II.5 Programming Language

Modelling Concepts
both first and last. Because DOG is alone in KENNEL(FARM), it has no predecessor or successor entities.
F.KENNEL
L.KENNEL
N.KENNEL
FARM
1
LICENSE
P.KENNEL
S.KENNEL
M.KENNEL
DOG
1 2 3
0
0
0
Figure 4-14. Entity Records
After the second DOG is created and filed, the entity records take the form shown in figure 4-15.
With two members in the set, the first and last pointers lead to different entity records. The first
entity, pointed to by F.KENNEL(FARM), points ahead to the second entity with its successor pointer.
The second entity points back at the first entity with its predecessor pointer. Both the predecessor
pointer of the first entity and the successor pointer of the last entity are zero, indicating their
respective roles.
F.KENNEL
L.KENNEL
N.KENNEL
FARM
2
LICENSE
P.KENNEL
S.KENNEL
M.KENNEL
1 2 3
0
0
DOG
LICENSE
248
P.KENNEL
0
S.KENNEL
M.KENNEL 0
Figure 4-15. Entity Records
An important point to note is that the global variable DOG now points to the second DOG created.
The entity record of the first DOG created can only be accessed through the pointers to it, L.KEN-
NEL(FARM) and S.KENNEL(DOG). These pointers illustrate the general form of an attribute reference:
attribute (entity identification)
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