Definitive XML Schema

PRISCILLA WALMSLEY is a prominent XML consultant with an international practice in XML architecture and implementation, SOA/Web services development, electronic publishing, data conversion, metadata management, and of course, XML Schema design and training. Priscilla is Managing Director of Datypic, Inc., which supports this book at datypic.com/books/defxmlschema2.

"XML Schema 1.1 has gone from strong data typing to positively stalwart-so powerful it can enforce database level constraints and business rules, so your data transfer code won't have to. This book covers the 1.1 changes-and more-in its 500 revisions to Priscilla Walmsley's 10-year best-selling classic. It's the guide you need to navigate XML Schema's complexity-and master its power!"

-Charles F. Goldfarb

For Ten Years the World's Favorite Guide to XML Schema-Now Extensively Revised for Version 1.1 and Today's Best Practices!

To leverage XML's full power, organizations need shared vocabularies based on XML Schema. For a full decade, Definitive XML Schema has been the most practical, accessible, and usable guide to working with XML Schema. Now, author Priscilla Walmsley has thoroughly updated her classic to fully reflect XML Schema 1.1, and to present new best practices for designing successful schemas.

Priscilla helped create XML Schema as a member of the W3C XML Schema Working Group, so she is well qualified to explain the W3C recommendation with insight and clarity. Her book teaches practical techniques for writing schemas to support any application, including many new use cases. You'll discover how XML Schema 1.1 provides a rigorous, complete specification for modeling XML document structure, content, and datatypes; and walk through the many aspects of designing and applying schemas, including composition, instance validation, documentation, and namespaces. Then, building on the fundamentals, Priscilla introduces powerful advanced techniques ranging from type derivation to identity constraints. This edition's extensive new coverage includes

Many new design hints, tips, and tricks - plus a full chapter on creating an enterprise strategy for schema development and maintenance
Design considerations in creating schemas for relational and object-oriented models, narrative content, and Web services
An all-new chapter on assertions
Coverage of new 1.1 features, including overrides, conditional type assignment, open content and more
Modernized rules for naming and design
Substantially updated coverage of extensibility, reuse, and versioning
And much more

If you're an XML developer, architect, or content specialist, with this Second Edition you can join the tens of thousands who rely on Definitive XML Schema for practical insights, deeper understanding, and solutions that work.

Foreword xxxi Acknowledgments xxxiii How to use this book xxxv Chapter 1 Schemas: An introduction 2 1.1 What is a schema? 3 1.2 The purpose of schemas 5 1.2.1 Data validation 5 1.2.2 A contract with trading partners 5 1.2.3 System documentation 6 1.2.4 Providing information to processors 6 1.2.5 Augmentation of data 6 1.2.6 Application information 6 1.3 Schema design 7 1.3.1 Accuracy and precision 7 1.3.2 Clarity 8 1.3.3 Broad applicability 8 1.4 Schema languages 9 1.4.1 Document Type Definition (DTD) 9 1.4.2 Schema requirements expand 10 1.4.3 W3C XML Schema 11 1.4.4 Other schema languages 12 1.4.4.1 RELAX NG 12 1.4.4.2 Schematron 13 Chapter 2 A quick tour of XML Schema 16 2.1 An example schema 17 2.2 The components of XML Schema 18 2.2.1 Declarations vs. definitions 18 2.2.2 Global vs. local components 19 2.3 Elements and attributes 20 2.3.1 The tag/type distinction 20 2.4 Types 21 2.4.1 Simple vs. complex types 21 2.4.2 Named vs. anonymous types 22 2.4.3 The type definition hierarchy 22 2.5 Simple types 23 2.5.1 Built-in simple types 23 2.5.2 Restricting simple types 24 2.5.3 List and union types 24 2.6 Complex types 25 2.6.1 Content types 25 2.6.2 Content models 26 2.6.3 Deriving complex types 27 2.7 Namespaces and XML Schema 28 2.8 Schema composition 29 2.9 Instances and schemas 30 2.10 Annotations 31 2.11 Advanced features 32 2.11.1 Named groups 32 2.11.2 Identity constraints 32 2.11.3 Substitution groups 32 2.11.4 Redefinition and overriding 33 2.11.5 Assertions 33 Chapter 3 Namespaces 34 3.1 Namespaces in XML 35 3.1.1 Namespace names 36 3.1.2 Namespace declarations and prefixes 37 3.1.3 Default namespace declarations 39 3.1.4 Name terminology 40 3.1.5 Scope of namespace declarations 41 3.1.6 Overriding namespace declarations 42 3.1.7 Undeclaring namespaces 43 3.1.8 Attributes and namespaces 44 3.1.9 A summary example 46 3.2 The relationship between namespaces and schemas 48 3.3 Using namespaces in schemas 48 3.3.1 Target namespaces 48 3.3.2 The XML Schema Namespace 50 3.3.3 The XML Schema Instance Namespace 51 3.3.4 The Version Control Namespace 51 3.3.5 Namespace declarations in schema documents 52 3.3.5.1 Map a prefix to the XML Schema Namespace 52 3.3.5.2 Map a prefix to the target namespace 53 3.3.5.3 Map prefixes to all namespaces 54 Chapter 4 Schema composition 56 4.1 Modularizing schema documents 57 4.2 Defining schema documents 58 4.3 Combining multiple schema documents 61 4.3.1 include 62 4.3.1.1 The syntax of includes 63 4.3.1.2 Chameleon includes 65 4.3.2 import 66 4.3.2.1 The syntax of imports 67 4.3.2.2 Multiple levels of imports 70 4.3.2.3 Multiple imports of the same namespace 72 4.4 Schema assembly considerations 75 4.4.1 Uniqueness of qualified names 75 4.4.2 Missing components 76 4.4.3 Schema document defaults 77 Chapter 5 Instances and schemas 78 5.1 Using the instance attributes 79 5.2 Schema processing 81 5.2.1 Validation 81 5.2.2 Augmenting the instance 82 5.3 Relating instances to schemas 83 5.3.1 Using hints in the instance 84 5.3.1.1 The xsi:schemaLocation attribute 84 5.3.1.2 The xsi:noNamespaceSchemaLocation attribute 86 5.4 The root element 87 Chapter 6 Element declarations 88 6.1 Global and local element declarations 89 6.1.1 Global element declarations 89 6.1.2 Local element declarations 93 6.1.3 Design hint: Should I use global or local element declarations? 95 6.2 Declaring the types of elements 96 6.3 Qualified vs. unqualified forms 98 6.3.1 Qualified local names 98 6.3.2 Unqualified local names 98 6.3.3 Using elementFormDefault 99 6.3.4 Using form 100 6.3.5 Default namespaces and unqualified names 101 6.4 Default and fixed values 101 6.4.1 Default values 102 6.4.2 Fixed values 103 6.5 Nils and nillability 105 6.5.1 Using xsi:nil in an instance 108 6.5.2 Making elements nillable 109 Chapter 7 Attribute declarations 112 7.1 Attributes vs. elements 113 7.2 Global and local attribute declarations 115 7.2.1 Global attribute declarations 115 7.2.2 Local attribute declarations 117 7.2.3 Design hint: Should I use global or local attributedeclarations? 119 7.3 Declaring the types of attributes 120 7.4 Qualified vs. unqualified forms 122 7.5 Default and fixed values 123 7.5.1 Default values 124 7.5.2 Fixed values 125 7.6 Inherited attributes 126 Chapter 8 Simple types 128 8.1 Simple type varieties 129 8.1.1 Design hint: How much should I break down my datavalues? 130 8.2 Simple type definitions 131 8.2.1 Named simple types 131 8.2.2 Anonymous simple types 132 8.2.3 Design hint: Should I use named or anonymous types? 133 8.3 Simple type restrictions 135 8.3.1 Defining a restriction 136 8.3.2 Overview of the facets 137 8.3.3 Inheriting and restricting facets 139 8.3.4 Fixed facets 140 8.3.4.1 Design hint: When should I fix a facet? 141 8.4 Facets 142 8.4.1 Bounds facets 142 8.4.2 Length facets 143 8.4.2.1 Design hint: What if I want to allow empty values? 143 8.4.2.2 Design hint: What if I want to restrict the length of an integer? 144 8.4.3 totalDigits and fractionDigits 145 8.4.4 Enumeration 145 8.4.5 Pattern 148 8.4.6 Assertion 150 8.4.7 Explicit Time Zone 150 8.4.8 Whitespace 151 8.5 Preventing simple type derivation 152 8.6 Implementation-defined types and facets 154 8.6.1 Implementation-defined types 154 8.6.2 Implementation-defined facets 155 Chapter 9 Regular expressions 158 9.1 The structure of a regular expression 159 9.2 Atoms 161 9.2.1 Normal characters 162 9.2.2 The wildcard escape character 164 9.2.3 Character class escapes 164 9.2.3.1 Single-character escapes 165 9.2.3.2 Multicharacter escapes 166 9.2.3.3 Category escapes 167 9.2.3.4 Block escapes 170 9.2.4 Character class expressions 171 9.2.4.1 Listing individual characters 171 9.2.4.2 Specifying a range 172 9.2.4.3 Combining individual characters and ranges 173 9.2.4.4 Negating a character class expression 173 9.2.4.5 Subtracting from a character class expression 174 9.2.4.6 Escaping rules for character class expressions 175 9.2.5 Parenthesized regular expressions 175 9.3 Quantifiers 176 9.4 Branches 177 Chapter 10 Union and list types 180 10.1 Varieties and derivation types 181 10.2 Union types 183 10.2.1 Defining union types 183 10.2.2 Restricting union types 185 10.2.3 Unions of unions 186 10.2.4 Specifying the member type in the instance 187 10.3 List types 188 10.3.1 Defining list types 188 10.3.2 Design hint: When should I use lists? 189 10.3.3 Restricting list types 190 10.3.3.1 Length facets 192 10.3.3.2 Enumeration facet 192 10.3.3.3 Pattern facet 194 10.3.4 Lists and strings 195 10.3.5 Lists of unions 196 10.3.6 Lists of lists 196 10.3.7 Restricting the item type 198 Chapter 11 Built-in simple types 200 11.1 The XML Schema type system 201 11.1.1 The type hierarchy 202 11.1.2 Value spaces and lexical spaces 204 11.1.3 Facets and built-in types 204 11.2 String-based types 205 11.2.1 string, normalizedString, and token 205 11.2.1.1 Design hint: Should I use string, normalizedString, or token? 207 11.2.2 Name 208 11.2.3 NCName 210 11.2.4 language 211 11.3 Numeric types 213 11.3.1 float and double 213 11.3.2 decimal 215 11.3.3 Integer types 217 11.3.3.1 Design hint: Is it an integer or a string? 220 11.4 Date and time types 221 11.4.1 date 221 11.4.2 time 222 11.4.3 dateTime 223 11.4.4 dateTimeStamp 224 11.4.5 gYear 225 11.4.6 gYearMonth 226 11.4.7 gMonth 227 11.4.8 gMonthDay 227 11.4.9 gDay 228 11.4.10 duration 229 11.4.11 yearMonthDuration 231 11.4.12 dayTimeDuration 232 11.4.13 Representing time zones 233 11.4.14 Facets 234 11.4.15 Date and time ordering 235 11.5 Legacy types 236 11.5.1 ID 236 11.5.2 IDREF 237 11.5.3 IDREFS 239 11.5.4 ENTITY 240 11.5.5 ENTITIES 242 11.5.6 NMTOKEN 243 11.5.7 NMTOKENS 244 11.5.8 NOTATION 245 11.6 Other types 246 11.6.1 QName 246 11.6.2 boolean 247 11.6.3 The binary types 248 11.6.4 anyURI 250 11.7 Comparing typed values 253 Chapter 12 Complex types 256 12.1 What are complex types? 257 12.2 Defining complex types 258 12.2.1 Named complex types 258 12.2.2 Anonymous complex types 260 12.2.3 Complex type alternatives 261 12.3 Content types 262 12.3.1 Simple content 262 12.3.2 Element-only content 264 12.3.3 Mixed content 264 12.3.4 Empty content 265 12.4 Using element declarations 266 12.4.1 Local element declarations 266 12.4.2 Element references 267 12.4.3 Duplication of element names 268 12.5 Using model groups 270 12.5.1 sequence groups 270 12.5.1.1 Design hint: Should I care about the order of elements? 272 12.5.2 choice groups 273 12.5.3 Nesting of sequence and choice groups 275 12.5.4 all groups 276 12.5.5 Named model group references 278 12.5.6 Deterministic content models 279 12.6 Using attribute declarations 281 12.6.1 Local attribute declarations 281 12.6.2 Attribute references 282 12.6.3 Attribute group references 284 12.6.4 Default attributes 284 12.7 Using wildcards 284 12.7.1 Element wildcards 285 12.7.1.1 Controlling the namespace of replacement elements 287 12.7.1.2 Controlling the strictness of validation 287 12.7.1.3 Negative wildcards 289 12.7.2 Open content models 292 12.7.2.1 Open content in a complex type 292 12.7.2.2 Default open content 295 12.7.3 Attribute wildcards 298 Chapter 13 Deriving complex types 300 13.1 Why derive types? 301 13.2 Restriction and extension 302 13.3 Simple content and complex content 303 13.3.1 simpleContent elements 303 13.3.2 complexContent elements 304 13.4 Complex type extensions 305 13.4.1 Simple content extensions 306 13.4.2 Complex content extensions 307 13.4.2.1 Extending choice groups 309 13.4.2.2 Extending all groups 310 13.4.2.3 Extending open content 311 13.4.3 Mixed content extensions 312 13.4.4 Empty content extensions 313 13.4.5 Attribute extensions 314 13.4.6 Attribute wildcard extensions 315 13.5 Complex type restrictions 316 13.5.1 Simple content restrictions 317 13.5.2 Complex content restrictions 318 13.5.2.1 Eliminating meaningless groups 320 13.5.2.2 Restricting element declarations 321 13.5.2.3 Restricting wildcards 322 13.5.2.4 Restricting groups 324 13.5.2.5 Restricting open content 329 13.5.3 Mixed content restrictions 331 13.5.4 Empty content restrictions 332 13.5.5 Attribute restrictions 333 13.5.6 Attribute wildcard restrictions 335 13.5.7 Restricting types from another namespace 337 13.5.7.1 Using targetNamespace on element and attribute declarations 339 13.6 Type substitution 341 13.7 Controlling type derivation and substitution 343 13.7.1 final: Preventing complex type derivation 343 13.7.2 block: Blocking substitution of derived types 344 13.7.3 Blocking type substitution in element declarations 346 13.7.4 abstract: Forcing derivation 346 Chapter 14 Assertions 350 14.1 Assertions 351 14.1.1 Assertions for simple types 353 14.1.1.1 Using XPath 2.0 operators 355 14.1.1.2 Using XPath 2.0 functions 357 14.1.1.3 Types and assertions 359 14.1.1.4 Inheriting simple type assertions 362 14.1.1.5 Assertions on list types 363 14.1.2 Assertions for complex types 365 14.1.2.1 Path expressions 367 14.1.2.2 Conditional expressions 369 14.1.2.3 Assertions in derived complex types 370 14.1.3 Assertions and namespaces 372 14.1.3.1 Using xpathDefaultNamespace 373 14.2 Conditional type assignment 375 14.2.1 The alternative element 376 14.2.2 Specifying conditional type assignment 377 14.2.3 Using XPath in the test attribute 378 14.2.4 The error type 380 14.2.5 Conditional type assignment and namespaces 381 14.2.6 Using inherited attributes in conditional type Assignment 382 Chapter 15 Named groups 384 15.1 Why named groups? 385 15.2 Named model groups 386 15.2.1 Defining named model groups 386 15.2.2 Referencing named model groups 388 15.2.2.1 Group references 388 15.2.2.2 Referencing a named model group in a complex type 389 15.2.2.3 Using all in named model groups 391 15.2.2.4 Named model groups referencing named model groups 392 15.3 Attribute groups 392 15.3.1 Defining attribute groups 393 15.3.2 Referencing attribute groups 395 15.3.2.1 Attribute group references 395 15.3.2.2 Referencing attribute groups in complex types 396 15.3.2.3 Duplicate attribute names 397 15.3.2.4 Duplicate attribute wildcard handling 398 15.3.2.5 Attribute groups referencing attribute groups 398 15.3.3 The default attribute group 399 15.4 Named groups and namespaces 401 15.5 Design hint: Named groups or complex type derivations? 403 Chapter 16 Substitution groups 406 16.1 Why substitution groups? 407 16.2 The substitution group hierarchy 408 16.3 Declaring a substitution group 409 16.4 Type constraints for substitution groups 412 16.5 Members in multiple groups 413 16.6 Alternatives to substitution groups 414 16.6.1 Reusable choice groups 414 16.6.2 Substituting a derived type in the instance 415 16.7 Controlling substitution groups 418 16.7.1 final: Preventing substitution group declarations 418 16.7.2 block: Blocking substitution in instances 419 16.7.3 abstract: Forcing substitution 420 Chapter 17 Identity constraints 422 17.1 Identity constraint categories 423 17.2 Design hint: Should I use ID/IDREF or key/keyref? 424 17.3 Structure of an identity constraint 424 17.4 Uniqueness constraints 426 17.5 Key constraints 428 17.6 Key references 430 17.6.1 Key references and scope 432 17.6.2 Key references and type equality 432 17.7 Selectors and fields 433 17.7.1 Selectors 433 17.7.2 Fields 434 17.8 XPath subset for identity constraints 435 17.9 Identity constraints and namespaces 439 17.9.1 Using xpathDefaultNamespace 441 17.10 Referencing identity constraints 442 Chapter 18 Redefining and overriding schema components 446 18.1 Redefinition 448 18.1.1 Redefinition basics 448 18.1.1.1 Include plus redefine 450 18.1.1.2 Redefine and namespaces 450 18.1.1.3 Pervasive impact 450 18.1.2 The mechanics of redefinition 451 18.1.3 Redefining simple types 452 18.1.4 Redefining complex types 453 18.1.5 Redefining named model groups 454 18.1.5.1 Defining a subset 454 18.1.5.2 Defining a superset 455 18.1.6 Redefining attribute groups 456 18.1.6.1 Defining a subset 457 18.1.6.2 Defining a superset 458 18.2 Overrides 459 18.2.1 Override basics 459 18.2.1.1 Include plus override 461 18.2.1.2 Override and namespaces 461 18.2.1.3 Pervasive impact 462 18.2.2 The mechanics of overriding components 462 18.2.3 Overriding simple types 464 18.2.4 Overriding complex types 465 18.2.5 Overriding element and attribute declarations 466 18.2.6 Overriding named groups 467 18.3 Risks of redefines and overrides 468 18.3.1 Risks of redefining or overriding types 468 18.3.2 Risks of redefining or overriding named groups 470 Chapter 19 Topics for DTD users 472 19.1 Element declarations 473 19.1.1 Simple types 474 19.1.2 Complex types with simple content 475 19.1.3 Complex types with complex content 476 19.1.4 Mixed content 478 19.1.5 Empty content 479 19.1.6 Any content 480 19.2 Attribute declarations 480 19.2.1 Attribute types 480 19.2.2 Enumerated attribute types 481 19.2.3 Notation attributes 482 19.2.4 Default values 482 19.3 Parameter entities for reuse 483 19.3.1 Reusing content models 484 19.3.2 Reusing attributes 485 19.4 Parameter entities for extensibility 486 19.4.1 Extensions for sequence groups 486 19.4.2 Extensions for choice groups 489 19.4.3 Attribute extensions 490 19.5 External parameter entities 492 19.6 General entities 493 19.6.1 Character and other parsed entities 493 19.6.2 Unparsed entities 493 19.7 Notations 493 19.7.1 Declaring a notation 494 19.7.2 Declaring a notation attribute 495 19.7.3 Notations and unparsed entities 496 19.8 Comments 497 19.9 Using DTDs and schemas together 499 Chapter 20 XML information modeling 500 20.1 Data modeling paradigms 502 20.2 Relational models 503 20.2.1 Entities and attributes 504 20.2.2 Relationships 507 20.2.2.1 One-to-one and one-to-many relationships 507 20.2.2.2 Many-to-many relationships 507 20.2.2.2.1 Approach #1: Use containment with repetition 508 20.2.2.2.2 Approach #2: Use containment with references 510 20.2.2.2.3 Approach #3: Use relationship elements 512 20.3 Modeling object-oriented concepts 514 20.3.1 Inheritance 514 20.3.2 Composition 519 20.4 Modeling web services 522 20.5 Considerations for narrative content 524 20.5.1 Semantics vs. style 524 20.5.1.1 Benefits of excluding styling 524 20.5.1.2 Rendition elements: "block" and "inline" 525 20.5.2 Considerations for schema design 526 20.5.2.1 Flexibility 526 20.5.2.2 Reusing existing vocabularies 526 20.5.2.3 Attributes are for metadata 526 20.5.2.4 Humans write the documents 527 20.6 Considerations for a hierarchical model 527 20.6.1 Intermediate elements 527 20.6.2 Wrapper lists 531 20.6.3 Level of granularity 532 20.6.4 Generic vs. specific elements 533 Chapter 21 Schema design and documentation 538 21.1 The importance of schema design 539 21.2 Uses for schemas 540 21.3 Schema design goals 542 21.3.1 Flexibility and extensibility 542 21.3.2 Reusability 543 21.3.3 Clarity and simplicity 545 21.3.3.1 Naming and documentation 545 21.3.3.2 Clarity of structure 546 21.3.3.3 Simplicity 546 21.3.4 Support for graceful versioning 547 21.3.5 Interoperability and tool compatibility 547 21.4 Developing a schema design strategy 548 21.5 Schema organization considerations 550 21.5.1 Global vs. local components 550 21.5.1.1 Russian Doll 551 21.5.1.2 Salami Slice 553 21.5.1.3 Venetian Blind 554 21.5.1.4 Garden of Eden 555 21.5.2 Modularizing schema documents 557 21.6 Naming considerations 559 21.6.1 Rules for valid XML names 559 21.6.2 Separators 560 21.6.3 Name length 560 21.6.4 Standard terms and abbreviations 561 21.6.5 Use of object terms 562 21.7 Namespace considerations 564 21.7.1 Whether to use namespaces 564 21.7.2 Organizing namespaces 565 21.7.2.1 Same namespace 565 21.7.2.2 Different namespaces 568 21.7.2.3 Chameleon namespaces 572 21.7.3 Qualified vs. unqualified forms 575 21.7.3.1 Qualified local names 575 21.7.3.2 Unqualified local names 576 21.7.3.3 Using form in schemas 576 21.7.3.4 Form and global element declarations 578 21.7.3.5 Default namespaces and unqualified names 578 21.7.3.6 Qualified vs. unqualified element names 579 21.7.3.7 Qualified vs. unqualified attribute names 580 21.8 Schema documentation 580 21.8.1 Annotations 581 21.8.2 User documentation 582 21.8.2.1 Documentation syntax 582 21.8.2.2 Data element definitions 584 21.8.2.3 Code documentation 585 21.8.2.4 Section comments 585 21.8.3 Application information 586 21.8.4 Non-native attributes 588 21.8.4.1 Design hint: Should I use annotations or non-native attributes? 589 21.8.5 Documenting namespaces 589 Chapter 22 Extensibility and reuse 594 22.1 Reuse 596 22.1.1 Reusing schema components 596 22.1.2 Creating schemas that are highly reusable 597 22.1.3 Developing a common components library 597 22.2 Extending schemas 599 22.2.1 Wildcards 601 22.2.2 Open content 604 22.2.3 Type substitution 605 22.2.4 Substitution groups 607 22.2.5 Type redefinition 609 22.2.6 Named group redefinition 611 22.2.7 Overrides 612 Chapter 23 Versioning 616 23.1 Schema compatibility 617 23.1.1 Backward compatibility 618 23.1.2 Forward compatibility 623 23.2 Using version numbers 626 23.2.1 Major and minor versions 626 23.2.2 Placement of version numbers 628 23.2.2.1 Version numbers in schema documents 628 23.2.2.2 Versions in schema locations 630 23.2.2.3 Versions in instances 631 23.2.2.4 Versions in namespace names 632 23.2.2.5 A combination strategy 633 23.3 Application compatibility 634 23.4 Lessening the impact of versioning 635 23.4.1 Define a versioning strategy 636 23.4.2 Make only necessary changes 636 23.4.3 Document all changes 637 23.4.4 Deprecate components before deleting them 638 23.4.5 Provide a conversion capability 639 23.5 Versions of the XML Schema language 639 23.5.1 New features in version 1.1 640 23.5.2 Forward compatibility of XML Schema 1.1 641 23.5.3 Portability of implementation-defined types and facets 642 23.5.3.1 Using typeAvailable and typeUnavailable 644 23.5.3.2 Using facetAvailable and facetUnavailable 645 Appendix A XSD keywords 648 A.1 Elements 649 A.2 Attributes 671 Appendix B Built-in simple types 690 B.1 Built-in simple types 691 B.2 Applicability of facets to built-in simple types 695 Index 699