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>GNADE User's Guide: GNADE, The GNat Ada Database Environment; Version 1.5.0; Document Revision $Revision: 1.42 $</TH
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>Chapter 21. Basic Concepts</H1
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>Hostvariables</A
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> This chpater gives an overview of the concepts of the ADBC
interface.
</P
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> The ADBC interface is based upon the following major components:
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>Hostvariables</P
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>Hostvariables</A
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> Host variables are used to transfer data between the data base and
the application. In a query the hostvariables are indicated by
a name preceeded by an ':' in a query. The API allowes to associcate
Ada 95 host variables with these names. An Ada 95 hostvariable
provides the value and the additional attribute Is_Null to the
application programmer, which means the variable is has a value
or is not set.
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>Driver dependencies: </B
> Not all database drivers do provide the null indication
for a colon in the result set. As a consequence the driver may
not be able to support this. The driver should always return true and
a defined value.
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