HP Integrity NonStop J-Series - Manual (Page 157)

USING AN ENABLE APPLICATION
Record Keys
If your application displays several boxes, it is important to
recognize the difference between an outermost box, a containing
box, and a nested box since:
• You must perform an operation (read or insert a record) on the
outermost box before you can perform an operation on any other
box.
• You must perform an operation (read or insert a record) on a
containing box before you can perform any operation on a
box nested within it.
RECORD KEYS
An application uses key fields, or record keys, to identify
specific records. You can quickly and efficiently select one
record from among thousands stored in a file by indicating a
record key. Three categories of record keys exist: primary keys,
alternate keys, and courtesy keys. A record cannot have both a
primary key and a courtesy key. A record can, however, have a
primary key and any number of alternate keys or a courtesy key
and any number of alternate keys.
Primary Key
An application can identify a particular record by the contents
of a primary key field. If a record has a primary key field of
the value 500, for example, you could retrieve that record by
requesting the record whose primary key value is equal to 500.
A primary key value is always unique; that is, the primary keys
of a file cannot contain duplicate values. Primary keys are
always sorted in ascending sequence; this means that if you read
through a file sequentially by primary key, the next record is
always the record with the next higher primary key value.
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