Enterprise SOA

1
Enterprise SOA

• Chapter 2
• Evolution of the Service Concept

2
Milestones of Enterprise Computing

• Web services sometimes means application
  services delivered to human users over the Web
• Web services sometimes means application
  modules made accessible to other applications
  over the Internet using XML-based protocols
• In this book web service means some meaningful
  activity that a computer program performs on
  behalf of another computer program

3
Milestones of Enterprise Computing

• A service is a remotely accessible,
  self-contained application module
• Application frontends make these services
  available to human users
• We will speak of service consumers and service
  providers
• Services provide abstraction from technical
  details including location and discovery
• Services are reusable in different applications

4
Milestones of Enterprise Computing

• A crucial factor in the development of services
  is the quest for the right degree of abstraction
• A service encapsulates a certain complexity
• An appropriate interaction pattern must exist
  between provider and user
• Services have developed out of ideas in reusable
  business functions on mainframes, remote
  procedure calls in networks, component-based and
  object-oriented languages,

5
Milestones of Enterprise Computing

• Roots of service-orientation is found in three
  areas
• Programming paradigms
• Distribution technology
• Business computing

6
Programming Paradigms

• Functional decomposition flow charts
• COBOL was suited to program decomposition
• Functional programming there are limits because
  multi-purpose functions are hard to create.
• Also, callers must provide lots of parms
• 1980s Modula, ADA
• Object-oriented languages

7
Programming Paradigms

• Objects offer highly reusable code, communicate
  with messages and offer inheritance
• Unfortunately, the level of abstraction and
  granularity exposed to a client is to fine to
  enable efficient reuse or distribution
• Service orientation tries to overcome problems
  with distributed computing by providing the right
  level of granularity and access patterns for
  remote services

8
Programming Paradigms

• Service orientation often goes backward (compared
  to OO) when considering how tightly data and
  functionality should be coupled
• Service orientation assumes that data and
  functionality is separate

9
Distributed Computing

• Developed in the last 30 years
• Computing once meant mainframes
• Multiuser, centralized power
• Unix adopted the network as an essential part
• Remote procedure call systems developed
• As relational databases developed, businesses
  adopted a client/server approach

10
Distributed Computing

• Blurring the client from the server was the next
  step
• CORBA used distributed processing of objects
• Mid 1990s clustering a set of objects on a
  single server to provide a higher level of
  abstraction and to enrich the service (EJB)
• EJB relies on a distributed model based on a
  controlled number of servers that host the
  objects
• EJB inspired by CORBA and CICS

11
Distributed Computing

• 1990s middleware solutions for distributed
  transaction management (Java Transaction Service,
  Microsoft Transaction Server)
• The number of middleware solutions led to
  middleware heterogeneity
• Mid 1990s XML becomes popular as a
  middleware-independent format for the exchange of
  data and documents
• XML is not bound to any particular technology

12
XML and SOAP

• XMLs flexibility requires higher-level data
  structures and messaging formats
• Many higher-level XML standards have emerged
• Microsoft invented SOAP allowing server to server
  communication over HTTP (web services)
• Microsoft created WSDL (Web Service Definition
  Language) as a way to describe intefaces for
  services
• While web services are ideally suited to SOAP and
  WSDL, the architecture is independent of
  technology