Chapter 23. Implementation-Specific Features

XQuery can be used for a wide variety of XML processing needs. As such, different XQuery implementations provide customized functions and settings for specific use cases. This chapter looks at some of the implementation-specific aspects of XQuery.

Conformance

The XQuery specification consists of a core set of features that all implementations are required to support. Supporting these features is known as minimal conformance. In addition, there are a handful of optional features that are clearly defined and scoped. These optional features are listed in Table 23-1.

Table 23-1. Features

Feature

Description

Chapter

Full Axis

Support for the axes ancestor, ancestor-or-self, following, following-sibling, preceding, preceding-sibling

4

Module

Support for library modules and module imports

12

Schema Import

Support for schema imports in the prolog

13

Schema Validation

Support for validate expressions

13

Static Typing

Detection of all static type errors in the analysis phase

14

Serialization

Ability to serialize query results to an XML document

22

In addition to these six features, some aspects of the core language are either implementation-dependent or implementation-defined. Implementation-defined features are those where the implementer is required to document the choices she has made. For example, the list of supported collations or additional built-in functions is implementation-defined. Implementation-dependent behavior may vary by implementation but does not have to be explicitly stated in the documentation and cannot necessarily be predicted. For example, when an unordered expression is used, the order of the results is implementation-dependent.

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