HP DDL D40, Справочное руководство

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Definition Attributes
Data Definition Language (DDL) Reference Manual — 426798-002
6- 35
SPI-NULL Clause
SPI-NULL Clause
The SPI-NULL clause specifies an Subsystem Programmatic Interface (SPI) null value
for a field or group definition of an SPI extensible structured token, or for a field or
group description within a group definition. The SPI-NULL clause is specified in a
DEFINITION statement referenced in the DEF IS clause of a TOKEN-MAP statement.
A field or group with an SPI null value in every byte is considered to have unspecified
data.
Use the SPI-NULL clause only if you plan to use SPI messages to communicate
among processes in a Distributed Systems Management (DSM) environment.
character
is any ASCII character enclosed in quotation marks.
number
is any number from 0 to 255; it must not be enclosed in quotation marks.
constant-name
is the name of a constant in the open DDL dictionary. The constant value must be
a valid
character
or
number
value.
SPI-NULL Clause Guidelines
The following points are guidelines for using the SPI-NULL clause:
•
The SPI-NULL value must fit in one byte.
•
The SPI-NULL clause differs from the NULL clause as follows:
°
The SPI-NULL clause is used only to assign an SPI null value to a field or a
group of fields that will be used in an SPI extensible structured token defined
by a TOKEN-MAP statement.
°
The NULL clause is used only to assign a null value to an alternate-key field
referenced in a RECORD statement.
•
Every field in a extensible structured token must have an SPI null value, whether
specified explicitly or implicitly by default.
•
For a field to contain an SPI null value, each byte of the field must contain the
value specified in the SPI-NULL clause. You use the SPI SSNULL procedure to fill
the field with the SPI null value specified in the SPI-NULL clause.
•
The SPI-NULL value for a bit field must be 255.
SPI-NULL {"character" | number | constant-name}