Chapter 11: Architectural Design

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Chapter 11 Architectural Design

• Yonsei University
• 2nd Semester, 2009
• Sanghyun Park

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Topics Covered

• System structuring
• Modular decomposition
• Control models
• Reference architectures

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Software Architecture

• Architectural design is the design process for
  identifying the __________ making up a system and
  the framework for sub-system _______ and
  communication
• The output of this design process is a
  description of the software __________

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Architectural Design

• An ______ stage of the system design process
• Represents the ____ between requirement
  specification and design processes
• In many cases, carried out in ______ with some
  specification activities
• Involves identifying major system components and
  their communications

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Architectural Design Process

• System structuring
• The system is decomposed into several
  principal___________ and communications between
  thesesub-systems are identified
• Modular decomposition
• The identified sub-systems are decomposed into
  ________
• Control modeling
• A model of the ________ relationships between the
  different parts of the system is established

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Sub-Systems And Modules

• A sub-system is a system in its own right whose
  operation is __________ of the services provided
  by other sub-systems
• A module is a system component that provides
  _______ to other components but would not
  normally be considered as an independent system

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Architectural Styles (1/3)

• The system architecture affects the performance,
  robustness, and maintainability of a system
• Therefore the particular style and structure
  chosen for an application may depend on the
  ____________ requirements

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Architectural Styles (2/3)

• Performance
• _______ critical operations and ________
  communications
• Use ______ rather than fine-grain components
• Security
• Use a _______ architecture with critical assets
  in the inner layers

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Architectural Styles (3/3)

• Safety
• _______ safety-critical operations in a small
  number of sub-systems
• Availability
• Include _________ components for fault tolerance
• Maintainability
• Use ____-grain, self-contained components

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Architectural Conflicts

• Using large-grain components improves ___________
  but reduces _____________
• Introducing redundant data improves ________ but
  makes _______ more difficult
• Localizing safety-related features usually means
  more ___________ so degraded ___________

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System Structuring(System Organization)

• Concerned with decomposing the system into
  interacting sub-systems
• The architectural design is normally expressed as
  a ______ diagram presenting an overview of the
  system structure (Figure 11.1)
• More specific models of the structure may be
  developed which show how systems share data, how
  they are distributed, and how they interface with
  each other

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Repository Model

• Sub-systems must exchange data this may be done
  in two ways
• Shared data is held in a central database or
  _________ and may be accessed by all sub-systems
• Each sub-system maintains its ____ database and
  passes data explicitly to other sub-systems
• When large amounts of data are to be shared,the
  _________ model of sharing is most commonly used

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CASE Toolset Architecture
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Repository Model Characteristics (1/2)

• Advantages
• Efficient way to share large amount of data
• Sub-systems which produce data need not be
  concerned with how that data is used by other
  sub-systems
• Activities such as backup, security, access
  control and recovery from error are _________
• Sharing model is published as the repository
  _______

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Repository Model Characteristics (2/2)

• Disadvantages
• Sub-systems must agree on a repository data model
• Data ________ is difficult and expensive
• No scope for specific management policies
• Difficult to _______ the repository over a number
  of machines

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Client-Server Model

• Distributed system model which shows how data and
  processing are distributed across a range of
  components
• Set of stand-alone ______ which provide specific
  services such as printing, data management, etc.
• Set of ______ which call on these services
• Network which allows clients to access servers

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Film And Picture Library
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Client-Server Characteristics

• Advantages
• Distribution of data is straightforward
• Makes effective use of _________ systems.May
  require _______ hardware
• Easy to add new servers or upgrade existing
  servers
• Disadvantages
• No shared data model so sub-systems use different
  data organization. Data __________ may be
  inefficient
• __________ management in each server
• No central _______ of names and services it may
  be hard to find out what servers and services are
  available

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Abstract Machine (Layered) Model

• Used to model the interfacing of sub-systems
• Organizes the system into a set of _____ each of
  which provides a set of services
• Each layer defines an _______ machine whose
  machine language is used to implement the next
  level of abstract machine
• When a layer interface changes, only the ______
  layer is affected
• Often difficult to structure systems in this way

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Version Management System
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Modular Decomposition

• Another structural level where sub-systems are
  decomposed into ________
• Two modular decomposition models covered
• An _____ model where the system is decomposed
  into interacting objects
• A function-oriented pipeline or ____-flow model
  where the system is decomposed into functional
  modules which ________ inputs to outputs

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Object Models

• Structure the system into a set of loosely
  coupled _______ with well-defined interfaces
• Object-oriented decomposition is concerned with
  identifying object ______, their attributes, and
  operations
• When implemented, objects are created from these
  classes and some control model used to coordinate
  object operations

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Invoice Processing System
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Object Model Advantages

• Objects are loosely coupledso their
  implementation can be modified without affecting
  other objects
• The objects may reflect ____-world entities
• OO implementation languages are widely used
• However, object ________ changes may cause
  problems and ______ entities may be hard to
  represent as objects

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Function-Oriented Pipelining(Data-Flow Models)

• Functional transformations process their inputs
  to produce outputs
• Variants of this approach are very common.When
  transformations are sequential with data
  processed in batches, this is a _____ sequential
  model
• Not really suitable for _________ systems

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Invoice Processing Systems
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Data-Flow Model Advantages

• Supports transformation ______
• Intuitive organization for stakeholder
  communication
• Easy to add new transformation
• Relatively simple to implementas either a
  concurrent or sequential system
• However, requires a _______ format for data
  transfer along the pipeline and difficult to
  support ______-based interaction

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Control Models

• Concerned with the control flow
  betweensub-systems
• Two general approaches can be identified
• Centralized approachOne sub-system has ______
  responsibility for control, and starts and stops
  other sub-systems
• Event-based approachEach sub-system can respond
  to events from other sub-systems or the systems
  environment

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Centralized Model

• A control sub-system takes responsibility for
  managing the execution of other sub-systems
• Call-return model
• Top-down _________ model where control starts at
  the top of a subroutine hierarchy and moves
  downwards
• Only applicable to _________ systems
• Manager model
• One system component is designated as a system
  manager and controls the starting, stopping, and
  coordination of other system processes
• Applicable to both sequential and _________
  systems

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Call-Return Model
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Manager Model
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Event-Based Control

• Driven by externally generated events where the
  _____ of the event is _______ the control of the
  sub-systems which process the event
• Two principal event-driven models
• Broadcast model
• Interrupt-driven model

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Broadcast Model

• An event is broadcast to all sub-systems. Any
  sub-system which can handle the event may do so
• Effective in __________ sub-systems on different
  computers in a network
• Sub-systems ______ an interest in specific
  events. When these occur, control is transferred
  to the sub-system which can handle the event
• Control policy is not embedded in the event and
  message handler. Sub-systems decide on events of
  interest to them

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Selective Broadcasting
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Interrupt-Driven Model (1/2)

• Used in ________ systems where interrupts are
  detected by an interrupt handler and passed to
  some other component for processing
• There are known interrupt types with a handler
  defined for each type
• Each type is associated with a memory _______ and
  a hardware switch causes transfer to its handler
• Allows fast response but ________ to program and
  difficult to _______

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Interrupt Driven Model (2/2)
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Reference Architectures

• Architectural models may be specific to some
  application _______
• Two types of domain-specific model
• Generic models which are abstractions from a
  number of _____ systems and which encapsulate the
  principal characteristics of these systems
• Reference models which are more abstract,
  idealized model. Mainly used to communicate
  domain ________ and compare different
  architectures
• Generic models are usually _________
  modelsReference models are ________ models

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Generic Models

• Compiler model is a well-known example although
  other models exist in more specialized
  application domains
• Lexical analyzer
• Symbol table
• Syntax analyzer
• Syntax tree
• Semantic analyzer
• Code generator
• Generic models may be reused directly in a design

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Reference Models

• Reference models are derived from a _____ ofthe
  application domain rather than from existing
  systems
• May be used as a basis for system implementation
  or to compare different systems
• Act as a standard against which systems can be
  evaluated
• OSI model is a layered model for communication
  systems

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OSI Reference Model
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Application
Application
Presentation
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Presentation
Session
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Session
Transport
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Transport
Network
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Network
Network
Data link
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Data link
Data link
Physical
1
Physical
Physical
Communications medium