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Part I: Fundamental Service Contract Design
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Chapter 3: SOA Fundamentals and Web Service Contracts
Chapter 4: Anatomy of a Web Service Contract
Chapter 5: A Plain English Guide to Namespaces
Chapter 6: Fundamental XML Schema: Types and Message Structure Basics
Chapter 7: Fundamental WSDL Part I: Abstract Description Design
Chapter 8: Fundamental WSDL Part II: Concrete Description Design
Chapter 9: Fundamental WSDL 2.0: New Features and Design Options
Chapter 10: Fundamental WS-Policy: Expression, Assertion, and Attachment
Chapter 11: Fundamental Message Design: SOAP Envelope Structure and Header Block Processing
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Chapter 3: SOA Fundamentals and Web Service Contracts (TOC)
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This chapter begins with an overview of key terms and concepts associated with SOA, service-orientation,
and service-oriented computing in general as they pertain to Web service
contract design.
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Chapter 4: Anatomy of a Web Service Contract (TOC)
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This introductory chapter provides a visual exploration of Web service contract structures
from both logical and physical perspectives. The focus is on establishing a conceptual
understanding of the various parts that can comprise a Web service contract and
the mechanics that make these parts work together.
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Concepts pertaining to abstract and concrete descriptions are discussed in relation to
message, operation, and port type (interface) definitions, along with different message
parts, such as the body, header, and headerfault. Also covered are the binding, service,
and port (endpoint) sections and how they relate to message parts (body, header, headerfault),
envelope structure, and each other.
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This chapter contains no code examples and only begins discussing the actual technologies
used to build Web service contracts after the basics have been covered in abstract.
The final section concludes the chapter with a series of guidelines.
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Chapter 5: A Plain English Guide to Namespaces (TOC)
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As an integral part of the XML-based Web services framework, both custom and predefined
namespaces are used to ensure that all of the technologies covered in this book
can harmoniously work together. Therefore, before we get into the actual technology
languages used to build Web service contracts, we first provide an informal but in-depth
tutorial about namespaces.
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Because the topic of namespaces represents a common point of confusion for many IT
professionals, this chapter takes extra time to explain the concepts and applications of
namespaces in plain English. A range of examples and perspectives are provided so
that you are fully prepared for any namespace-related issues discussed in subsequent
chapters.
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Chapter 6: Fundamental XML Schema: Types and Message Structure Basics (TOC)
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We now begin to get into the details of contract design with a chapter dedicated to
describing basic XML Schema topics, as they pertain to message design for Web service
contracts. The emphasis is on different types of constraints for complex and simple
types. Also provided is coverage of how XML Schema types can be customized and
extended using type inheritance features.
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This chapter also officially kicks off the case study by introducing a set of problems that
are solved via the application of XML Schema features. The examples explored ultimately
lead to the creation of a set of XML Schema types that will be used by message
definitions in the following chapters.
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Chapter 7: Fundamental WSDL Part I: Abstract Description Design (TOC)
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In this chapter we discuss all aspects of the Web Services Description Language (WSDL)
1.1 that relate to designing and building the parts that comprise the abstract service
description. This includes the association of XML Schema types with message definitions,
the organization of messages into operation definitions, and the grouping of operations
within port type definitions. Also covered is the creation of message headers and
the usage of the various namespaces required for different technologies to co-exist
within a WSDL document.
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Through a series of informal case study examples a complete abstract description is created,
incorporating the XML Schema types that were defined in Chapter 6.
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Chapter 8: Fundamental WSDL Part II: Concrete Description Design (TOC)
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We now move on to the design and development of the concrete description, the part of
the WSDL document that binds the abstract description to actual transport and messaging
protocols and also assigns it one or more physical network addresses.
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This chapter covers all of the primary WSDL 1.1 language elements used to establish this
binding, including the service and port definitions, as well as the important binding construct
itself. A great deal of content is dedicated to exploring how these native WSDL
elements are further supplemented via the use of extensibility elements from other languages,
such as SOAP. How header and headerfault message parts are bound to actual
SOAP message areas is also described.
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The case study examples continue and culminate in the creation of a complete WSDL
definition that includes both the abstract and concrete descriptions.
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Chapter 9: Fundamental WSDL 2.0: New Features and Design Options (TOC)
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This book also covers the WSDL 2.0 standard, which introduces new features and
imposes a series of syntactical changes to the WSDL 1.1 language. Through a series of
examples, this chapter documents the differences between WSDL 1.1 and 2.0 as they pertain
to both abstract and concrete descriptions, and then concludes with a complete
WSDL 2.0 version of the WSDL document from Chapter 8.
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Chapter 10: Fundamental WS-Policy: Expression, Assertion, and Attachment (TOC)
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Through the creation of policy assertions and policy expressions, the WS-Policy language
provides various means of extending the technical interface that you can create
with WSDL and XML Schema.
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This chapter introduces the basics of how policies can be defined and expressed and
then associated (attached) to different parts of a WSDL document. Topics include policy
subjects, policy alternatives, composite policies, and embedded and external attachment
options.
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The examples again lead to a revised WSDL definition that includes a simple, attached
policy expression.
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Chapter 11: Fundamental Message Design: SOAP Envelope Structure and Header
Block Processing (TOC)
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We now turn our attention to the SOAP technology language that is used to express the
structure of messages as they exist “on the wire,” when they are transmitted to and from
Web services. Although this book is dedicated to the Web service contract only, it is
important to understand how messages will be processed in order for us to design them
effectively.
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Aprimary topic in this chapter is the runtime usage of SOAP header blocks and the various
roles and options that exist to carry out “targeted processing” where header blocks
are designed to be accessed and used only by certain programs along a message path.
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Note that this chapter does not explain the SOAP communications framework or any
other topics that do not pertain directly to Web service contract design.
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Part II: Advanced Service Contract Design
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Chapter 12: Advanced XML Schema Part I: Message Flexibility and Type Inheritance and Composition
Chapter 13: Advanced XML Schema Part II: Reusability, Derived Types, Relational Design
Chapter 14: Advanced WSDL Part I: Modularization, Extensibility, MEPs, and Asynchrony
Chapter 15: Advanced WSDL Part II: Message Dispatch, Service Instance Identification, and Non-SOAP
HTTP Binding
Chapter 16: Advanced WS-Policy Part I: Policy Centralization and Nested, Parameterized, and Ignorable
Assertions
Chapter 17: Advanced WS-Policy Part II: Custom Policy Assertion Design, Runtime Representation, and
Compatibility
Chapter 18: Advanced Message Design Part I: WS-Addressing Vocabularies
Chapter 19: Advanced Message Design Part II: WS-Addressing Rules and Design Techniques
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Chapter 12: Advanced XML Schema Part I: Message Flexibility and Type Inheritance
and Composition (TOC)
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There are a variety of messages that a Web service will need to exchange, each with its
own unique requirements. This, the first of two chapters dedicated to advanced XML
Schema topics, explores the usage of wildcards, extension buckets, and content model
groups and documents a variety of techniques that use these XML Schema features to
accommodate different types of Web service message designs.
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The chapter then continues with an explanation of type inheritance and composition
and further discusses how cross-schema inheritance, as a concept, may have different
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implications than cross-service inheritance. Specifically, this part of the chapter provides
examples that detail how abstract schemas can be created and how schemas in general
can be extended.
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Finally, a discussion of message design in support of CRUD-style Web service operations
is provided. Individual Add, Get, Delete, and Update message designs are
described, along with common granularity levels.e 9
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Chapter 13: Advanced XML Schema Part II: Reusability, Derived Types, Relational Design (TOC)
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The ability to share schemas across Web services is fundamental to establishing separate
schema and contract architecture layers. This chapter delves into the various options by
which schemas can be partitioned into reusable modules and then included or imported
by different schemas (and, ultimately, different WSDL definitions). The creation of a
common schema library is furthermore discussed and demonstrated.
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Next are sections dedicated to explaining how relational data structures can be simulated
using XML Schema features and also how narrative content can be added to supplement
base schema content. Finally, the usage and incorporation of pre-defined
industry schemas is explored along with several examples and techniques.
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Chapter 14: Advanced WSDL Part I: Modularization, Extensibility, MEPs, and Asynchrony (TOC)
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Both WSDL 1.1 and 2.0 modularization features and techniques are covered and demonstrated
in this chapter, along with issues pertaining to non-transitive limitations that
also relate the reuse of XML Schema definitions across WSDL definitions. The use of
WSDL import and include are compared, along with WSDL 2.0 interface inheritance
design options.
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This is followed by a comprehensive exploration of various WSDL extensibility elements
and how they can be used and positioned within the WSDL definition structure,
with an emphasis on the WSDL binding construct.
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Subsequent sections discuss special message exchange patterns (including WSDL 1.1
outbound MEPs and the WSDL 2.0 Robust In-Only MEP) and various advanced techniques
for asynchronous message exchanges involving HTTP, SOAP, and SMTP.
Finally, a section dedicated to WS-BPEL related extensibility elements is provided along
with recommendations as to how to best prepare WSDL definitions for eventual composition
by WS-BPEL process definitions.
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Chapter 15: Advanced WSDL Part II: Message Dispatch, Service Instance Identification,
and Non-SOAP HTTP Binding (TOC)
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Various advanced WSDL techniques are explored in this chapter, including the use of
new WSDL 2.0 features that allow for broad message coupling. A section dedicated to
message dispatch design issues is also provided, along with guidelines as to how to
leverage the SOAP Action value to support interpretation of WSDL definitions for dispatch
purposes.
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Additional topics include different approaches for Web service instance identification
and creating header blocks, including the use of the header fault extension. Finally, the
binding of WSDL to HTTP without SOAP is explored and demonstrated for both WSDL
1.1 and 2.0.
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Chapter 16: Advanced WS-Policy Part I: Policy Centralization and Nested, Parameterized,
and Ignorable Assertions (TOC)
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Continuing the coverage of the WS-Policy framework that began in Chapter 10, we now
delve into various architectural issues, including the application of the Policy Centralization
design pattern and different potential approaches for associating separate policy
definition documents with WSDL definitions.
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Subsequent parts of this chapter demonstrate the use of nested and parameterized policy
expressions and then provide detailed coverage of ignorable policy assertions,
including a comparison with optional policy assertions. The chapter concludes with an
overview of concurrent policy-enabled Web service contracts.
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Chapter 17: Advanced WS-Policy Part II: Custom Policy Assertion Design, Runtime
Representation, and Compatibility (TOC)
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This chapter describes the design process and implications behind creating custom
policy assertions. Various examples demonstrate different types of assertions and the
pros and cons of customizing policies are further explained. A separate section is provided,
dedicated to issues pertaining to the maintenance of custom policy assertion
vocabularies.
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Later in the chapter, the runtime representation or policy syntax is explored to provide
insight as to how policy expressions and alternatives are streamlined into normalized
representations. Finally, an intersection algorithm is explained to identify compatibility
between service provider and consumer policies.
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Chapter 18: Advanced Message Design Part I: WS-Addressing Vocabularies (TOC)
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WS-Addressing provides an industry-standard means of extending the base SOAP message
design to accommodate a wide range of complex message exchange requirements.
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This chapter formally introduces the WS-Addressing standard by individually describing
the language elements and SOAP headers established by the Endpoint References
(EPR) and Message Addressing Properties (MAP) vocabularies. The chapter provides
numerous code samples and concludes with a case study example comprised of a complete
set of WS-Addressing headers.
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Chapter 19: Advanced Message Design Part II: WS-Addressing Rules and Design
Techniques (TOC)
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Various, more specialized topics in relation to WS-Addressing are covered in this chapter,
including EPR parameter mapping techniques, design issues relating to the binding
of Endpoint References with WSDL definitions, and a detailed comparison of
WS-Addressing Action values to alternative SOAP Action expressions. The chapter concludes
with descriptions of policy assertions provided and standardized by the WSAddressing
specification.
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Part III: Service Contract Versioning
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Chapter 20: Versioning Fundamentals
Chapter 21: Versioning WSDL Definitions
Chapter 22: Versioning Message Schemas
Chapter 23: Advanced Versioning
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Chapter 20: Versioning Fundamentals (TOC)
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Basic concepts and terminology associated with Web service contract versioning are
established in this chapter, together with a detailed explanation of forward and backward
compatibility from both technical and governance perspectives.
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Version identification is then described and demonstrated through the use of annotated
version numbers and namespace values. The chapter ends with sections that describe
three primary versioning strategies (Strict, Flexible, Loose) that each support forward
and backward compatibility to different extents. These strategies will be used for reference
purposes throughout subsequent chapters.
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Chapter 21: Versioning WSDL Definitions (TOC)
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This chapter explores different techniques for versioning different parts of a WSDL
definition with an emphasis on the versioning of WSDL operations. Separate sections
provide versioning guidance and examples for adding, renaming, and removing operations
as well as modifying operation message exchange patterns and associated fault
messages.
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Also provided are techniques for versioning port type definitions and various parts of
the concrete description. The last section describes what parts of the WSDL language can
be used to potentially support forward compatibility.
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Chapter 22: Versioning Message Schemas (TOC)
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The complex topic of XML Schema-based message versioning is tackled in this chapter,
which groups techniques as per the three versioning strategies established in Chapter
20. Versioning approaches to adding, removing, renaming, and modifying existing XML
Schema components are documented separately in relation to each versioning strategy.
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Throughout these sections various XML Schema language features are explored, including
the use of wildcards for forward compatibility and optional elements to accommodate
backward compatibility. Another primary topic addressed throughout this chapter
is the use of XML Schema namespaces for versioning purposes.
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Chapter 23: Advanced Versioning (TOC)
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This final chapter provides a mixed bag of versioning guidelines, techniques, and design
considerations. It starts off with versioning strategies specifically for WS-Policy expressions
and assertions, and then continues with design methods that use policy assertions
to express termination information and explore the utilization of custom attributes to
express non-ignorable unknown elements (when using wildcards).
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Various other versioning approaches are covered, several based on actual contract versioning
design patterns, such as Partial Understanding. The chapter concludes with a
series of tips for creating and customizing your own versioning strategy.
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Part IV: Appendices
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The remaining appendices conclude this book with further supporting content.
Appendix A: Case Study Conclusion
Appendix B: How Technology Standards are Developed
Appendix C: Alphabetical Pseudo Schema Reference
Appendix D: Alphabetical Pseudo Schema Reference
Appendix E: SOA Design Patterns Related to this Book
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Appendix A: Case Study Conclusion (TOC)
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This appendix provides a brief summary and conclusion of the case study storyline, as
it pertains to the Web service contracts designed within the ActionCon IT enterprise
environment.
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Appendix B: How Technology Standards are Developed (TOC)
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A concise overview of how the W3C organizes its technical committees is provided,
along with descriptions of the processes and stages through which submitted specifications
are developed into ratified standards.
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Appendix C: Alphabetical Pseudo Schema Reference (TOC)
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Skeleton pseudo Schemas are supplied for all of the language elements explained in this
book. These Schemas are listed in alphabetical order for quick reference purposes.
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Appendix D: Namespaces and Prefixes Used in this Book (TOC)
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A reference list of the namespaces and associated prefixes used in previous chapters.
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Appendix E: SOA Design Patterns Related to this Book (TOC)
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Concise descriptions of each of the design patterns referenced and discused
throughout this book. Note that these pattern descriptions are also available online at
www.soapatterns.org.
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Part I: Fundamental Service Contract Design
