Chapter 4: Enterprise Architectures

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• Chapter 4Enterprise Architectures

Service-Oriented Computing Semantics, Processes,
Agents Munindar P. Singh and Michael N. Huhns,
Wiley, 2005
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Highlights of this Chapter

• Enterprise Integration
• JEE
• .NET
• Model Driven Architecture
• Legacy Systems

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JEE Technology
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.NET Technology
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.NET Web Services

• COBOL Web service for multiplication (Mikes
  joke)
• lt_at_ webservice language''COBOL'' gt
• CLASS-ID. MULTIPLICATIONSERVICE.
• FACTORY.
• PROCEDURE DIVISION.
• METHOD-ID. MULTIPLY.
• DATA DIVISION.
• LINKAGE SECTION.
• 01 VAL-1 PIC S9(9) COMP-5.
• 02 VAL-2 PIC S9(9) COMP-5.
• 01 PRODUCT PIC S9(9) COMP-5.
• PROCEDURE DIVISION USING BY VALUE VAL-1 VAL-2
  RETURNING PRODUCT.
• COMPUTE PRODUCT VAL-1 VAL-2.
• END METHOD MULTIPLY.
• END FACTORY.
• END CLASS MULTIPLICATIONSERVICE.

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Legacy Systems

• A pejorative term for computing systems that
• Run on obsolete hardware and nonstandard networks
• Run poorly documented, unmaintainable software
• Consist of poorly modeled databases
• Support rigid user interfaces
• Notice that legacy systems is not synonymous
  with mainframe
• Mainframes have had a resurgence in the last
  decade no longer obsolete hardware often
  support modern OSs (Linux) not necessarily
  poorly modeled or rigid (some elements are
  obsolete or arcane)
• Most problems are with software whether on
  mainframes or other machines

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How Legacy Systems Arise

• Proprietary software
• not supporting industry standards
• (vendors who hope to lock in the market through
  incompatibility)
• Meaning embedded procedurally in the code
• Ad hoc changes to software in response to
• changing requirements, because of changes in
  laws, regulations, competition, or other business
  needs
• bugs

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Legacy Systems Pros and Cons

• Fulfill crucial business functions
• Run the worlds airline reservation systems
• Run most air traffic control programs
• Have dedicated users
• Represent huge investments in time and money
• Complicate reuse and sharing of data and programs
  cause redundancy, wasted effort, and integrity
  violations

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Migration

• Updating technology is
• Essential
• A continual process
• All at once?
• Expensive
• Risky
• Brittle
• Frustrating for users
• Gradual change dismantle legacy and build
  desired system hand-in-hand
• Install and test piecemeal

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Applying Services
New Service
Services Refactored from Legacy Backend
Application
Legacy Backend
Legacy Interface
Error services at too coarse a granularity
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Chapter 4 Summary

• Services must fit into existing architectures
• J2EE and .NET are architecturally quite similar
• Legacy systems provide the basis for many modern
  services
• They host key data and processes
• Interoperating with them is nontrivial
• Challenge refactoring legacy capabilities to
  derive best value from resulting services