ServiceOriented DesignPart I: Introduction

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Chapter 13

• Service-Oriented Design(Part I Introduction)

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Introduction to Service Oriented Design

• Service-Oriented Design is the process by which
  concrete physical service designs are derived
  from logical service candidates and then
  assembled into abstract compositions that
  implement a business process.

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Primary questions answered by this phase

• How can physical service interface definitions be
  derived from the service candidates modeled
  during the service-oriented phase?
• What SOA characteristics do we want to realize
  and support?
• What industry standards and extensions will be
  required by our SOA to implement the planned
  service designs and SOA characteristics?

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Overall goals

• Determine the core set of architectural
  extensions.
• Set the boundaries of the architecture.
• Identify the required design standards.
• Define abstract service interface designs.
• Identify potential service compositions.
• Assess support for service-orientation
  principles.
• Explore support for characteristics of
  contemporary SOA.

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Design standards vs. Industry Standards

• Design Standards represent custom standards
  created by an organization to ensure that
  services and SOAs are built according to a set of
  consistent conventions.
• Industry Standards are provided by standards
  organizations and are published in Web Services
  and XML specifications.

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The Service-oriented design process

• First establish a parent process that begins with
  preparatory work.
• Leads to a series of iterative processes that
  govern the creation of different types of service
  designs and the design of the overall solution
  workflow.

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Step 1 Compose SOA

• Underlying architecture needs to be well defined.
• Asks us to formally define a standard set of
  service layers, then choose open technologies in
  support of those layers.

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Step 2 to 4 Design Services

• Steps are represented by three following
  services
• Entity-centric business service design process.
• Application service design process.
• Task-centric business service design process.

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Step 5 Design service-oriented business process

• Create our orchestration layer the glue that
  binds our services with business process logic.
• Translates into the creation of a WS-BPEL process
  definition.

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XML Schema Definition Language (XSD)

• XML Schema definition describes what can be in
  an XML document.
• XSD schemas provide data types to represent
  information in XML document instances.

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The schema element

• Schema element is the root of every XSD schema.
• Contains series of common attributes used
  primarily to establish important namespace
  references.
• Tells the XML parser that it is an XSD schema.

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The element element

• Can declare a custom element that is referenced
  by its name within an XML document instance
• type attribute can be set to one of the
  predefined data types established by the XML
  schema specification

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complexType

• Can group elements and attributes into a
  composite type that can be used to represent a
  set of related date representations
• These can be assigned to one or more elements,
  facilitating standardization and reuse of
  commonly grouped information
• Avoids redundant element declarations
• sequence element established a specific order for
  element elements

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simpleType

• Allows you to group related data representations
  also, but they cannot contain attributes or
  further child elements

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import and include elements

• Used to point to the locations of the XSD schema
  file that will be pulled in when the schema is
  processed at runtime
• include used to reference schemas that use the
  same target namespace as parent schema
• import points to schemas that use a different
  target namespace

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WSDL

• Web Services Description Language
• Most fundamental technology standard associated
  with the design of services

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definition element

• The root or parent element of every WSDL document
• Location in which the many namespaces used within
  WSDL documents are established

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types element

• Is where XSD schema content is placed
• Can consist of actual XSD schema markup
• Can contain import elements that reference
  external schema definitions
• Not a required element

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message and part schema

• For every message a service is designed to
  receive or transmit, a message construct must be
  added
• Assigns the message a name and contains one or
  more part child elements that are each assigned a
  type
• part elements identify the data type of the
  message part

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portType, interface, and operation element

• Service operations are defined within portType
  area
• Represents collections of operations
• Individual operations are defined using operation
  element
• Version 2.0 specification changes portType name
  to interface

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input and output elements(when used operation)

• operation contains input and/or output child
  elements
• Represent the request and response messages the
  operation is capable of processing

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binding element

• Assigns a communication protocol that can be used
  to access and interact with the WSDL

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input and output element(when used with binding)

• Do not reference the message elements again
• Contain protocols details that establish how the
  messages are processed and interpreted

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service, port, and endpoint elements

• service element provides a physical address at
  which the service can be accessed
• port element contains a soapaddress element with
  physical address information
• port is replaced with endpoint element in version
  2.0 WSDL specification

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import element

• Import parts of WSDL definition as well as XSD
  schemas

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documentation element

• Optional element
• Allows you to add descriptive, human-readable
  annotations within a WSDL definition

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envelope element

• Represents the root of SOAP message structures
• Contains mandatory Body construct and optional
  Header construct

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Header element

• Key enabler of feature set provided by WS-
  specifications

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Body element

• The one required child element of SOAP Envelope
  construct

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Fault element

• Optional, provides a ready made error response
  that is added inside the Body construct

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3 common approaches to working with WSDL and XML
Schema markup language

• Autogeneration
• Design Tools
• Hand Coding

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Autogeneration

• WSDL and XSD schema markup code can be
  auto-generated with a development utility
• Common for efficiently generating a service
  interface that mirrors the interface of
  distributed back-end component
• Highly discouraged within SOAs, opposed
  preference of WS- specifications for a
  document-style message model

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Design tools

• Drag and drop of elements allowed
• Assemble a service interface without having to
  type out markup syntax

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Hand Coding

• Writing out code in text editor or XML editor