This document describes the expressions available in X-Query. The names of the expressions correspond to the language constructs of X-Query. In many cases, these are equivalent to an XPath expression of the same name. However, in a few cases the meaning is different or the expression only exists in X-Query, since its serves a special purpose in the context of a database. A syntax diagram illustrates the definition as it appears in the respective production rule of the X-Query grammar. The description is followed by an XPath compatibility note and one or more examples.
The most basic parts of the X-Query language are not covered; we
summarize them here. Digits, numbers, and operators are defined as in the
lexical rules of the XPath specification (in
Section 3.7).
However, X-Query adds to the list of operators the special contains operator
~=, which provides text retrieval capabilities. The list of
operator names (OperatorName, defined in XPath,
Section 3.7, Rule
33) is extended by adj, after,
before, betw, between,
near, intersect. All of these additions are described
below.
The following table lists the expressions available in X-Query, along
with the corresponding XPath expressions. An asterisk (*) after
the name of an XPath expression indicates that this expression is implemented
differently in X-Query. The link in the XPath column leads you to the
expression's production rule in the XPath specification.
| X-Query Expression | XPath Expression | Short Description |
|---|---|---|
AbbrevAbsoluteLocPath |
AbbreviatedAbsoluteLocationPath |
select all nodes satisfying some condition |
AbbreviatedAxisSpecifier |
AbbreviatedAxisSpecifier |
specify either child or attribute axis |
AbbreviatedStep |
AbbreviatedStep |
select context node or its parent node |
AbsoluteLocationPath |
AbsoluteLocationPath |
location path starting at the root node |
AdditiveExpr |
AdditiveExpr |
add or subtract numeric values |
AndExpr |
AndExpr |
check if two or more conditions are all true |
Argument |
Argument |
input to a FunctionCall |
AxisName |
AxisName * |
specify axis by name |
AxisSpecifier |
AxisSpecifier |
specify axis in a location step |
BetweenExpr |
— | select nodes based on a value range |
EqualityExpr |
EqualityExpr * |
check if two values are equal |
Expr |
Expr |
general X-Query expression |
FilterExpr |
FilterExpr * |
select a subset of nodes satisfying some condition |
FunctionCall |
FunctionCall |
call to a function |
LocationPath |
LocationPath |
select nodes along a path |
MultiplicativeExpr |
MultiplicativeExpr |
perform multiplication, division and modulo operations |
NameTest |
NameTest |
check for name of specified node |
NodeTest |
NodeTest * |
check for type or name of specified node |
NodeType |
NodeType * |
token representing a type of node |
OrExpr |
OrExpr |
check if one of the given conditions is true |
PathExpr |
PathExpr |
select a set of nodes |
Predicate |
Predicate |
select a subset of nodes for which the predicate is true |
PredicateExpr |
PredicateExpr |
expression used in a predicate |
PrimaryExpr |
PrimaryExpr |
expression without operators |
ProximityExpr |
— | specify adjacent values |
RelationalExpr |
RelationalExpr |
compare two numeric values |
RelativeLocationPath |
RelativeLocationPath |
select nodes relative to the context node |
SequenceExpr |
— | select nodes based on sibling positioning |
SetExpr |
UnionExpr * |
select union or intersection of node sets |
SortByClause |
— | sort a node set |
SortByCharacteristics |
— | determine sorting order |
Step |
Step |
select a subset of nodes on a given axis |
UnaryExpr |
UnaryExpr |
change number sign |
