[e-mail]

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Real-Time System Development ?????? SOA Service-O
riented Architecture

• ???
• cwhsueh_at_csie.ntu.edu.tw
• http//www.csie.ntu.edu.tw/chsueh/
• 95 Fall

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Preface

• ??????????????
• ???????, 930618, ???
• ??????????, 930929,???,???????????????
• Enterprise Middleware
• SOA
• "Things should be made as simple as possible, but
  no simpler." -- Albert Einstein
• Simple is not easy!

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Focus on Enterprise Middleware

• Why?
• Who?
• What?
• When?
• Where?
• How?

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Introduction to SOA

• Service-Oriented Architecture
• a Standard fOr Architecture description
• Society Of Actuary
• Society Of Ancients

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What is an Architecture?

• "The architecture of an IT system is the
  structure or structures of the system, which
  comprise software and hardware components, the
  externally visible properties of those
  components, and the relationships among them."
  (Adapted from Bass et al.1)

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What is a Service-Oriented Architecture (SOA)?

• SOA is an architectural style whose goal is to
  achieve loose coupling among interacting software
  agents.
• A service is a unit of work done by a service
  provider to achieve desired end results for a
  service consumer.
• Both provider and consumer are roles played by
  software agents on behalf of their owners.

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Service-Oriented Architecture (1)

• An accepted industry model for representing
  applications on the network as reusable services.
  
• Various interface standards exist for these
  services.
• range from DCE/RPC and CORBA,
• DCE source code is now available under an Open
  Source license (LGPL).
• through stored procedures
• to Web Services.
• An architectural style whose goal is to achieve
  loose coupling among interacting software agents.

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Service-Oriented Architecture (2)

• In all cases, requests are made of the services
  by a calling application that expects some form
  of reply often referred to as request/reply.
• A fundamental element of Service-Oriented
  Architectures is the separation of interface from
  implementation.
• This enables a more loose coupling between the
  service consumer and the service provider.
• The separation is enabled by means of a metadata
  layer that makes the interface definition
  available at design time.

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How does SOA achieve loose coupling?

• Employing two architectural constraints
• A small set of simple and ubiquitous interfaces
  to all participating software agents.
• Only generic semantics are encoded at the
  interfaces.
• The interfaces should be universally available
  for all providers and consumers.
• Descriptive messages constrained by an extensible
  schema delivered through the interfaces.
• No, or only minimal, system behavior is
  prescribed by messages.
• A schema limits the vocabulary and structure of
  messages.
• An extensible schema allows new versions of
  services to be introduced without breaking
  existing services.

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Additional Constraints

• There are a number of additional constraints one
  can apply on SOA in order to improve its
  scalability, performance and, reliability.
• Stateless Service
• Stateful Service
• Idempotent Request

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Deriving Web Services from SOA

• A web service is a SOA with at least the
  following additional constraints
• Interfaces must be based on Internet protocols
  such as HTTP, FTP, and SMTP.
• Except for binary data attachment, messages must
  be in XML
• There are two main styles of Web services SOAP
  web services and REST web services.

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SOAP Web services

• Except for binary data attachment, messages must
  be carried by SOAP.
• The description of a service must be in WSDL.
• A SOAP RPC web service breaks the second
  constraint required by an SOA.

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REST Web Services

• Interfaces are limited to HTTP. The following
  semantics are defined
• HTTP GET is used for obtaining a representation
  of a resource. A consumer uses it to retrieve a
  representation from a URI. Services provided
  through this interface must not incur any
  obligation from consumers.
• HTTP DELETE is used for removing representations
  of a resource.
• HTTP POST is used for updating or creating the
  representations of a resource.
• HTTP PUT is used for creating representations of
  a resource.
• Most messages are in XML, confined by a schema
  written in a schema language such as XML Schema
  from W3C or RELAX NG.
• Simple messages can be encoded with URL encoding.
  
• Service and service providers must be resources
  while a consumer can be a resource.

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An SOAnot just Web services

• Within a business environment, a pure
  architectural definition of an SOA might be an
  application architecture within which all
  functions are defined as independent services
  with well-defined invokable interfaces, which can
  be called in defined sequences to form business
  processes.
• two critical characteristics to be realized
• the services are truly independent,
• they can be managed.

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Management includes

• Security
• to authorize requests, encrypt and decrypt data
  as required, and validate information.
• Deployment
• to allow the service to be moved around the
  network to maximize performance or eliminate
  redundancy to provide optimum availability.
• Logging
• to provide auditing and metering capabilities.
• Dynamic rerouting
• to provide fail-over or load-balancing
  capabilities.
• Maintenance
• to manage new versions of the service.

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What is a service?

• a simple business capability
• getStockQuote, getCustomerAddress or
  checkCreditRating
• a more complex business transaction
• commitInventory, sellCoveredOption or
  scheduleDelivery
• a system service
• logMessageIn, authenticateUser

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Why migrating to a service-oriented architecture?

• Problems
• Complexity
• Enterprise Application Integration (EAI) tops the
  priority list of many CIOs
• redundant and nonreusable programming
• as a result of mergers and acquisitions
• multiple interfaces
• the n(n-1) integration problem

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What about the future?

• Java technology has provided platform-neutral
  programming.
• XML has provided self-describing,
  platform-neutral data.
• Web services have removed another barrier by
  allowing applications to interconnect in an
  object-model-neutral way.
• For example, using a simple XML-based messaging
  scheme, Java applications can invoke Microsoft
  .NET applications or CORBA-compliant, or even
  COBOL, applications.

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Common Misconceptions about SOA

1. Web services are just like distributed objects
2. Web services is RPC for the Internet
3. Web Services need HTTP
4. Web services need web servers
5. Web services are reliable because they use TCP
6. Web services debugging is impossible

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Distributed Computing Environment (DCE)

• LGPL
• ?

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Enterprise Workframe Architecture
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Where to Open?
J2EE .NET CORBA DCOM DCE Websphere Biztalk
Back-end
Front-end


Company A Service 1
interfaces to open
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Enterprise Middleware Platform
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open
open
open
middlewares
Open ?? Middleware Interface
Open Interface Platform
J2EE, CORBA, .NET,
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Reference

• ????????
• http//w2kdmz1.moea.gov.tw/chief/up/930618???????.
  ppt
• http//w2kdmz1.moea.gov.tw/chief/up/930929????????
  ??.ppt
• What is Architecture?
• What is Service-Oriented Architecture?
• Migrating to a service-oriented architecture
• Web Services are not Distributed Objects Common
  Misconceptions about Service Oriented
  Architectures
• What is Distributed Computing and DCE?