HP Integrity NonStop J-Series - Manual (Page 97)

CREATING AND RUNNING A MULTIFILE APPLICATION
Associating and Linking Boxes
When you establish a link between two boxes, you must decide
which box is to be the parent box and which box is to be the
child.
Choosing a Parent and Child Box
To decide which box is to be a parent box and which box is to be
a child, consider the purpose for which the application is being
generated. ENABLE imposes two requirements regarding this
choice:
1. The join field of a child box must be a primary key field, an
alternate key field, a courtesy key field, or the leading
portion of a primary or alternate key field.
2. The size of the join field for the parent box must be equal
to or less than the size of the join field of the child box.
Refer to the ENABLE Reference Manual for more information about
these requirements.
After you determine the links that can exist between the boxes
used by your application, you must identify the level at which
each box resides in the tree structure.
The Levels of the Tree Structure
A simple tree structure, such as the one you build for a
single-file application, has one level and a single box that
resides at that level. A more complex structure, such as one
that you build for an application that accesses several files,
can have many levels, with several boxes residing at each level
except for the first. At this, lowest, level there can be only
one box. ENABLE imposes no restrictions on the number of boxes
that reside at other levels of the tree structure and has a
maximum of 50 levels per application.
Before you identify the level at which each box resides, you
should understand how they affect the generated application.
When you identify the levels of your tree structure:
1. Only one box can reside at the first level. A box that
resides at this level must have one or more join fields that
you can use to link it to a child box (or boxes) at the
second level of the tree.
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