Query Processor Directive.
A Pragma is part of the query prolog and provides directives
for processing the query. In general, pragmas are extension
expressions which are expressions whose semantics are
implementation-defined. In Tamino, pragmas are syntactically similar to
processing instructions. However, they are called query processing
instructions (QPI) and are denoted by curly braces as delimiters instead
of angle brackets:
"{?" + PragmaName + " " + PragmaContents + " "* +"?}"
Note that the pragma name must immediately follow the opening delimiter
while this is not required for the closing delimiter, so
{?explain?} is valid, while {? explain ?} is not. The
following pragmas are available
TaminoQPIOptimization sets parameter for optimizing
certain parts of query processing.
TaminoQPIExecution sets parameter for tuning execution of
user-defined functions.
TaminoQPIInline determines a strategy for inlining
user-defined functions.
TaminoQPIExplain retrieves the query execution plan.
SerializationSpec determines the way Tamino serializes the
query result.
Note:
The syntax proposed for pragmas in recent working drafts of the XQuery
standard is not supported so that using "(::" and
"::)" as delimiters yields a syntax
error.
The following construct(s) refer to this construct: