Representation of XDM values
Values returned by XPath expressions in the s9api interface are represented as instances of the
class net.sf.saxon.s9api.XdmValue.
The XdmValue class is also used to supply parameters to stylesheets and transformations,
and to return the results of XSLT or XQuery evaluation.
The subclasses of XdmValue directly reflect the XDM model:
These objects are generally immutable.
A variety of methods are provided to convert between these classes and "ordinary" Java equivalents. For example
an XdmAtomicValue can be constructed directly from a Java boolean, String, long,
BigDecimal, or Instant (inter alia), and methods such as getBooleanValue()
and getStringValue() are available to convert in the other direction.
As an alternative to use of XPath, the select() method on XdmValue provides powerful
navigation capability around XDM trees. The select() method takes as argument a
Step (which is
a function from one node to related nodes) and returns an XdmStream of nodes as a result. There
is a library (Steps)
of Step functions corresponding to all the XPath axes, and the results of applying a Step
can be filtered using predicates: there is also a library (Predicates) of commonly-used
Predicates.
For example, if root is a document node, then root.select(descendant("p")).asXdmValue()
selects all the descendant elements with local name "p" in the form of an XdmValue.
The XdmNode class in this hierarchy is implemented as a wrapper around the lower-level NodeInfo
interface which provides more detailed access to information associated with nodes. The NodeInfo interface
is designed primarily for internal use within Saxon, whereas XdmNode is designed for application use.