An Introduction to Software Architecture

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An Introduction to Software Architecture
2
Contents

• What is Architecture?
• Current Practice in Software Architecture
• Why Software Architecture?
• Common Architecture Styles

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What is Architecture?

• Architecture the underlying structure of things
• An example of civil engineering
• Customer engineer gets customer requirements
• functional units
• 3 bedrooms, 21/2 bathrooms, 1 living
  1 dining rooms, 2-car garage,
  kitchen, backyard
•  other considerations
• cost, esthetics, workmanship, neighborhood,
  maintainability,
• economics

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What is Architecture?

• Architect starts thinking about architectural
  styles
• architectural styles
• Victorian, Duplex, Condominium, Townhouse,
  Catheral, Pyramidal,
• floor plans elevations for functional
  units
• Designers/Contractors think about detailed design
  considerations
• electrical wiring, plumbing, heating,
  air-conditioning, carpeting, etc.
• Sub-contractors/Construction Workers
• electricians, plumbers, furnace installers,
  carpenters, locksmith, brick layers, bathtub
  technicians, etc.

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Current Practice in Software Architecture

• Architecture Descriptions
• Camelot is based on the client-server model and
  uses remote procedure calls  both locally and
  remotely to provide communication among
  applications and servers.
• We have chosen a distributed, object-oriented
  approach to managing information.

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Current Practice in Software Architecture

• Observations
• software architectures are indeed used, very
  often but without even knowing it
• carries some, and more often than not a lot of,
  information
• no explicit description of the structure

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Software Architecture Description

• elements (components/parts)
• from which systems are built,e.g., process,
  data, object, agent
• interactions (connections/connectors/glues/relatio
  nships)
• between the elements,e.g., PCs, RPCs, MOMs,
  events
•  patterns
• describe layout of elements and interactions,
  guiding their composition, e.g., of elements,
  of connectors, order, topology, directionality

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Software Architecture Description

• constraints
•  on the patterns (i.e., on components,
  connectors, layout),e.g., temporal, cardinality,
  concurrency, (a)synchronous, etc.
•  styles
•  abstraction of architectural components from
  various specific architectures, (Sometimes
  interchangeably used with patterns,e.g., Unix OS,
  OSI protocol layer, Onion ring IS structure -gt
  layering
•  rationale
• describe why the particular architecture is
  chosen

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Why Software Architecture?

• abstract solution to conquer complexity
• supports reuse
• facilitates (integration) testing
• parallel development
• system evolvability
• many other conceptual reasons

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Common Architecture Styles

• Dataflow systems  
• Batch sequential
• Pipe Filter
• Call-and-return systems
• Main program subroutine
• OO systems
• Hierarchical layers
•  Independent components
• Communicating processes
• Event systems

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Common Architecture Styles

• Virtual machines
• Interpreters
• Rule-based systems
• Data-centered systems
• Databases
• Hypertext systems
• Blackboards
•  Process-control paradigms

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The KWIC Problem

• The KWIC (Key Word in Context) index system
  (functional requirements)
• accepts an ordered set of lines, (where)
•  each line is an ordered set of words, and
•  each word is an ordered set of characters.
•  any line may be "circularly shifted"
•  by repeatedly removing the first word and
  appending it at the end of the line.
•   the KWIC index system
•   outputs a listing of all circular shifts of all
  line in alphabetical order

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The KWIC Problem

• Input 1
• HOW ARCHITECTURE WINS TECHNOLOGY WARS
• HOW ARCHITECTURE WINS TECHNOLOGY WARS
•  ARCHITECTURE WINS TECHNOLOGY WARS HOW
•  WINS TECHNOLOGY WARS HOW ARCHITECTURE
•  TECHNOLOGY WARS HOW ARCHITECTURE WINS
•  WARS HOW ARCHITECTURE WINS TECHNOLOGY
• Input 2
• THE ART OF SYSTEMS ARCHITECTING
• ART OF SYSTEMS ARCHITECTING THE
• OF SYSTEMS ARCHITECTING THE ART
• SYSTEMS ARCHITECTING THE ART OF
• ARCHITECTING THE ART OF SYSTEMS

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The KWIC Problem

• Output
• ARCHITECTING THE ART OF SYSTEMS
•  ARCHITECTURE WINS TECHNOLOGY WARS HOW
•  ART OF SYSTEMS ARCHITECTING THE
•  HOW ARCHITECTURE WINS TECHNOLOGY WARS
•  OF SYSTEMS ARCHITECTING THE ART
•  SYSTEMS ARCHITECTING THE ART OF
•  TECHNOLOGY WARS HOW ARCHITECTURE WINS
•  THE ART OF SYSTEMS ARCHITECTING
•  WARS HOW ARCHITECTURE WINS TECHNOLOGY
•  WINS TECHNOLOGY WARS HOW ARCHITECTURE

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The KWIC Problem

• Non-functional requirements
• modifiability
• Changes in process algorithms
• Changes in data representations
• enhanceability
• to eliminate noise words (e.g., "a", "an", "the)
  
• performance (space and time)
• reusability

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Architecture Alternative I
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Architecture Alternative II
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Architecture Alternative III
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Architecture Alternative IV
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Contents of this presentation is from
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