The database server expects a particular prototype for each purpose function. As the access-method developer, you program the actions of a purpose function but must use the parameters and return values that the VTI prototypes specify. This section lists purpose-function prototypes in alphabetical order.
For each purpose function that your access method provides, use the prototype that this chapter shows, but change the prototype-function name to a unique name. For example, you might save your version of am_open with the name vtable_open(). To associate the unique purpose-function names to the corresponding prototype names, use the CREATE PRIMARYACCESS_METHOD statement, as CREATE ACCESS_METHOD (+) specifies.
The parameter list for each purpose function includes (by reference) one or more descriptor data structures that describe the SQL statement keywords or oncheck options and the specified table that requires the access method. For detailed information about each descriptor, refer to Descriptors.
Purpose functions are simply entry points from which the access method calls other routines from the access-method library, DataBlade API functions, and the VTI functions that Accessor Functions describes.
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