2 Basics

---

This section describes how DataDirect XQuery supports the following XQuery basics.

Expression Context
Processing Model
Error Handling
Concepts
Types
Comments

Expression Context

Table A-1 describes the XQuery expression context for DataDirect XQuery.

Table A-1. XQuery Expression Context 

XQuery Language		Support
Static context
	XPath 1.0 compatibility mode	This setting is always false as required by the XQuery specification.
	Statically known namespaces	Supported. See Namespaces for details on predefined namespaces.
	Default element/type namespace	The default value is no namespace. This value can be set in the query prolog.
	Default function namespace	The default value is http://www.w3.org/2005/ xpath-functions. This value can be set in the query prolog.
	In-scope schema definitions	Only predeclared types are supported. See Supported XQuery Atomic Types for a list of supported types.
	In-scope variables	This is determined by the XQuery expression.
	Context item static type	Supported except for initial context item.
	Function signatures	See Functions and Operators for a list of supported XQuery functions. User-defined functions are also supported.
	Statically known collations	The collations supported by the Java Virtual Machine.
	Default collation	Either the Java Virtual Machine collation or the one specified in the source configuration file. For relational sources, the default value is the collation used by the database. To ensure consistency, make sure that the collation used by the Java Virtual Machine is compatible with the collation used by the database. If multiple databases are used, make sure that their collations are compatible. See Specifying Collations for instructions on specifying collations.
	Construction mode	Supported with comment: preserve is supported. strip is not supported.
	Ordering mode	Supported.
	Default order for empty sequences	The following algorithm is used: The default is empty least. The default is overwritten by the default ordering behavior of the first JDBC connection defined using XQJ or the source configuration file. The default ordering of the first JDBC connection is defined by the database: DB2: empty greatest Informix: empty least Microsoft SQL Server: empty least Oracle: empty greatest PostgreSQL: empty greatest Sybase: empty least
	Boundary-space policy	The default value is strip (white space is removed during processing). This value may be set in the query prolog.
	Copy-namespaces mode	inherit,preserve mode is supported.
	Base URI	Supported. You can set this value in the query prolog or in the DDXQDataSource class by configuring the BaseUri property.
	Statically known documents	Not supported.
	Statically known collections	Data types of the data stored in database tables that can be referenced with fn:collection() are statically known although these data types cannot be accessed from within the expression. See Data Type Mappings for a list of supported data types.
	Statically known default collection type	Not supported.
Dynamic context
	Context item	Supported, except for initial context item.
	Context position	Supported. Context-position dependent expressions are compensated for relational sources.
	Context size	Supported.
	Variable values	Supported.
	Function implementations	Supported.
	Current dateTime	Supported. The current date and time are obtained from the Java Virtual Machine; however, queries executed against relational databases use the current date and time of the database server.
	Implicit timezone (implementation-defined)	Supported. The timezone is obtained from the Java Virtual Machine; however, queries executed against relational databases use the current timezone of the database server.
	Available documents	Supported. Available documents include XML files accessed through http:, ftp:, and file: URI schemes using fn:doc(). See XML Data Sources for rules governing URIs.
	Available collections	Supported. Available collections are determined by which connections are configured. See Specifying Relational Database Tables for details.
	Default collection	Not supported.

Processing Model

Table A-2 describes how the XQuery processing model relates to DataDirect XQuery.

Table A-2. XQuery Processing Model 

XQuery Language		Support
Data Model Generation		For a description of data model generation from XML, see Data Model Representation of XML Documents. For a description of data model generation from relational sources, see Data Model Representation of Relational Tables.
Schema import processing		Not supported.
Expression processing		Supported.
Serialization		Supported through XQJ. See Serialization Support for details.
Consistency constraints		DataDirect XQuery adheres to the consistency constraints as listed in this section of the XQuery specification.

Error Handling

Table A-3 describes how DataDirect XQuery handles errors.

Table A-3. Error Handling 

XQuery Language		Support
Error reporting		Supported. The static typing feature is also supported.

Concepts

Table A-4 describes how DataDirect XQuery works with some key concepts defined by XQuery.

Table A-4. XQuery Documents 

XQuery Language		Support
Document order		Supported.
Atomization		Supported.
Effective Boolean value		Supported.
Input sources		See fn:doc (15.5.4) and fn:collection (15.5.6).
URI literals		Supported.

Types

Table A-5 describes how DataDirect XQuery handles XQuery types.

Table A-5. XQuery Types 

XQuery Language		Support
Predefined schema types		Supported. See Supported XQuery Atomic Types for a list of supported atomic types.
Typed value and string value		Supported.
SequenceType syntax		Supported.
SequenceType matching		Supported. For queries evaluated against a relational database, cardinality testing is not performed.

Comments

Table A-6 describes how DataDirect XQuery supports comments.

Table A-6. Comments

XQuery Language		Support
Comments		Supported.