XQuery: Search Across a Variety of XML Data

736 Pages·2015·8.15 MB·English

by  Priscilla Walmsley

SECOND EDITION
XQuery
Priscilla Walmsley
Boston
XQuery
by Priscilla Walmsley
Copyright © 2015 Priscilla Walmsley. All rights reserved.
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Table of Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
1. Introduction to XQuery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
What Is XQuery? 23
Capabilities of XQuery 23
Uses for XQuery 24
Processing Scenarios 24
Easing into XQuery 25
Path Expressions 27
FLWORs 29
Adding XML Elements and Attributes 30
Adding Elements 30
Adding Attributes 32
Functions 33
Joins 33
Aggregating and Grouping Values 34
2. XQuery Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
The Design of the XQuery Language 35
XQuery in Context 36
XQuery and XPath 36
XQuery Versus XSLT 36
XQuery Versus SQL 37
XQuery and XML Schema 37
Processing Queries 38
Input Documents 38
The Query 39
The Context 40
iii
The Query Processor 40
The Results of the Query 40
The XQuery Data Model 41
Nodes 42
Atomic Values 46
Sequences 47
Types 48
Namespaces 48
3. Expressions: XQuery Building Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Categories of Expressions 51
Keywords and Names 52
Whitespace in Queries 53
Literals 53
Variables 54
Function Calls 54
Comments 55
Precedence and Parentheses 55
Comparison Expressions 57
General Comparisons 57
Value Comparisons 58
Node Comparisons 60
Conditional (if-then-else) Expressions 61
Conditional Expressions and Effective Boolean Value 62
Nesting Conditional Expressions 63
Switch Expressions 63
Logical (and/or) Expressions 65
Precedence of Logical Expressions 65
Negating a Boolean Value 66
4. Navigating XML Using Paths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Path Expressions 69
Path Expressions and Context 70
Steps 71
Axes 71
Node Tests 72
Abbreviated Syntax 75
Other Expressions As Steps 76
Predicates 77
Comparisons in Predicates 78
Using Positions in Predicates 78
Using Multiple Predicates 81
iv | Table of Contents
More Complex Predicates 82
A Closer Look at Context 83
Working with the Context Node 83
Accessing the Root 84
Dynamic Paths 85
The Simple Map Operator 85
5. Adding Elements and Attributes to Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Including Elements and Attributes from the Input Document 87
Direct Element Constructors 88
Containing Literal Characters 89
Containing Other Element Constructors 90
Containing Enclosed Expressions 90
Specifying Attributes Directly 93
Declaring Namespaces in Direct Constructors 94
Use Case: Modifying an Element from the Input Document 95
Direct Element Constructors and Whitespace 96
Computed Constructors 99
Computed Element Constructors 99
Computed Attribute Constructors 102
Use Case: Turning Content to Markup 102
6. Selecting and Joining Using FLWORs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Selecting with Path Expressions 105
FLWOR Expressions 105
The for Clause 108
The let Clause 110
The where Clause 112
The return Clause 113
The Scope of Variables 113
Quantified Expressions 114
Binding Multiple Variables 115
Selecting Distinct Values 116
Joins 117
Three-Way Joins 118
Outer Joins 119
Joins and Types 120
7. Sorting and Grouping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Sorting in XQuery 121
The order by Clause 121
The sort Function 125
Table of Contents | v
Document Order 125
Document Order Comparisons 127
Reversing the Order 128
Indicating That Order Is Not Significant 128
Grouping 130
Grouping Using the group by Clause 131
Aggregating Values 134
Ignoring “Missing” Values 136
Counting “Missing” Values 136
Aggregating on Multiple Values 137
Constraining and Sorting on Aggregated Values 138
8. Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Built-in Versus User-Defined Functions 141
Calling Functions 141
Function Names 142
Function Signatures 143
Argument Lists 143
Sequence Types 145
Calling Functions with the Arrow Operator 146
User-Defined Functions 146
Why Define Your Own Functions? 146
Function Declarations 147
The Function Body 148
The Function Name 149
The Parameter List 149
Functions and Context 152
Recursive Functions 152
9. Advanced Queries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Working with Positions and Sequence Numbers 155
Adding Sequence Numbers to Results 155
Using the count Clause 157
Testing for the Last Item 159
Windowing 160
Using start and end Conditions 162
Windows Based on Position 163
Windows Based on Previous or Next Items 164
Sliding Windows 166
Copying Input Elements with Modifications 166
Adding Attributes to an Element 167
Removing Attributes from an Element 168
vi | Table of Contents
Removing Attributes from All Descendants 169
Removing Child Elements 169
Changing Names 170
Combining Results 172
Sequence Constructors 172
The union Expression 172
The intersect Expression 173
The except Expression 173
Using Intermediate XML Documents 174
Creating Lookup Tables 174
Reducing Complexity 175
10. Namespaces and XQuery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
XML Namespaces 177
Namespace URIs 177
Declaring Namespaces 178
Default Namespace Declarations 179
Namespaces and Attributes 180
Namespace Declarations and Scope 180
Namespaces and XQuery 181
Namespace Declarations in Queries 182
Predeclared Namespaces 182
Prolog Namespace Declarations 183
Namespace Declarations in Direct Element Constructors 186
Namespace Declarations in Computed Constructors 187
The Impact and Scope of Namespace Declarations 188
Controlling Namespace Declarations in Your Results 190
In-Scope Versus Statically Known Namespaces 190
Controlling the Copying of Namespace Declarations 193
URI-Qualified Names 197
11. A Closer Look at Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
The XQuery Type System 199
Advantages of a Strong Type System 199
Do You Need to Care About Types? 200
The Built-in Types 201
Types, Nodes, and Atomic Values 203
Nodes and Types 203
Atomic Values and Types 204
Type Checking in XQuery 204
The Static Analysis Phase 205
The Dynamic Evaluation Phase 205
Table of Contents | vii
Automatic Type Conversions 205
Subtype Substitution 206
Type Promotion 206
Casting of Untyped Values 206
Atomization 206
Effective Boolean Value 207
Function Conversion Rules 209
Sequence Types 210
Occurrence Indicators 211
Generic Sequence Types 212
Atomic Type Names As Sequence Types 213
Element and Attribute Tests 213
Sequence Type Matching 214
The instance of Expression 214
Constructors and Casting 215
Constructors 215
The Cast Expression 216
The Castable Expression 217
Casting Rules 217
12. Prologs, Modules and Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Structure of a Query: Prolog and Body 221
Prolog Declarations 222
The Version Declaration 223
Assembling Queries from Multiple Modules 224
Library Modules 225
Importing a Library Module 225
Loading a Library Module Dynamically 227
Variable Declarations 228
Variable Declaration Syntax 228
The Scope of Variables 229
Variable Names 229
Initializing Expressions 229
External Variables 230
Private Functions and Variables 230
Declaring External Functions 231
13. Inputs and Outputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Types of Input and Output Documents 233
Accessing Input Documents 234
Accessing a Single Document with a Function 234
Accessing a Collection 235
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Setting the Context Outside the Query 236
Using Variables 236
Setting the Context in the Prolog 237
Serializing Output 237
Serialization Methods 238
Serialization Parameters 240
Specifying Serialization Parameters Using Option Declarations 244
Specifying Serialization Parameters Using a Separate XML Document 245
Serialization Errors 245
14. Using Schemas with XQuery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
What Is a Schema? 247
Why Use Schemas with Queries? 248
W3C XML Schema: A Brief Overview 249
Element and Attribute Declarations 250
Types 250
Namespaces and XML Schema 252
In-Scope Schema Definitions 253
Where Do In-Scope Schema Definitions Come from? 253
Schema Imports 253
Schema Validation and Type Assignment 255
The Validate Expression 256
Validation Mode 257
Assigning Type Annotations to Nodes 258
Nodes and Typed Values 259
Types and Newly Constructed Elements and Attributes 260
Sequence Types and Schemas 261
15. Static Typing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
What Is Static Typing? 265
Obvious Static Type Errors 266
Static Typing and Schemas 266
Raising “False” Errors 267
Static Typing Expressions and Constructs 267
The Typeswitch Expression 268
The Treat Expression 270
Type Declarations 271
Type Declarations in FLWORs 271
Type Declarations in Quantified Expressions 272
Type Declarations in Global Variable Declarations 272
The zero-or-one, one-or-more, and exactly-one Functions 273
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