SWE 316: Software Design and Architecture
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To understand
… the goals of software architecture
… the meaning of “frameworks”
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To be able to express a software architecture
… build frameworks
… complete a detailed design Ch 14
Adapted from Software Design: From
Programming to Architecture by Eric J.
Braude (Wiley 2003), with permission.
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

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Requirements
Analysis
Process Phases Discussed in This Chapter
Framework
Design
Architecture Detailed Design
Key: x = main emphasis x = secondary emphasis
Implementation
Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.
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What is a software architecture?
An architecture for a software application is its high level
design, enabling software engineers to gain understanding
An early stage of the system design process
It involves identifying major system components and their communications
Represents the link between specification and design processes
14.1
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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Architectural Design:
Establishing the overall structure of a software system
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The design process for identifying the sub-systems making up a system and the framework for subsystem control and communication is architectural design
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The output of this design process is a description of the software architecture
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser
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Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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If the application is small (e.g. 10 classes) this decomposition may be considered as architecture.
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In UML, If the application is big (hundreds of classes) we may group the classes into packages, so
Software architecture is a decomposition of application into a small number of packages (class collections)
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Framework: a collection of classes applicable to multiple applications
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
An Architecture for a Video Store Application
Videos Rentals
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Customers
Architecture is a high-level design
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
A Sequence for Obtaining The Class Model
0. Framework (some or all pre-existing)
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More general
2. Create architecture
-- typically use framework
1. Create domain classes
-- from requirements analysis
3. Create remaining design classes
-- to complete the class model
-- possibly use framework
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
To express requirements, architecture & detailed design
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Use-case model
“Do this ...” e.g.*, engage foreign character
Class model
“with objects of these classes ...” e.g., with Engagement … classes
Target
Application
Data Flow model
“in this way ...” e.g., character scores flow from
… to …
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser
State model
“reacting to these events ...” e.g., when foreign character enters
* Video game example

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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Three organizational dispositions to new systems
Integrate new systems into existing systems
Install support services for the first time
 Replace existing systems
Design deployment architecture
Type of infrastructure (i.e. Internet, Client/Server, Command)
Hardware environment (i.e. mainframe, mid-range servers, etc.)
Use existing infrastructure (i.e. single sign-on, networks, Internet access)
Architectural design issues for all organizations
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Reliability
Security
Performance
Usability
Supportability
Object-Oriented Analysis and
Design with the Unified Process
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Introduction Deployment Arch SW Architecture DataFlow Independent
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Design goals (review)
Correctness
Sufficiency
Robustness
Flexibility
Reusability
Efficiency
VM Repository Layered
14.3
Can be handled at lower levels of design
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Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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It is not hard to write small programs
However, large applications are difficult to create
14.3.2
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The principal problem 
Decomposing the problem (modularization) is an effective tool against complexity
The designer should form a clear mental model of how the application will work at a high level then
Develop a decomposition to match the mental model
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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Goals of software decomposition: Cohesion & Coupling
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Cohesion within a module is the degree to which communication takes place among the module’s elements
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Coupling is the degree to which modules depend directly on other modules
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Effective modularization is accomplished by
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 maximizing cohesion and minimizing coupling
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent
Cohesion and Coupling
2
1
3
VM component
Repository Layered
Fig 14.16
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High cohesion
 component
5 Bridge 6
Low coupling
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Steel truss component
High coupling 
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

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VM Repository Layered
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SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

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Architecture and Modularization of Encounter Video Game
EncounterGame
EncounterGame
«facade»
EncounterCharacters
EncounterCast
«facade» EncounterEnvironment
EncounterEnvironment
«facade»
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
Figure 14.19 Selecting a Basic Architecture
1. Develop a mental model of the application.
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 as if it were a small application e.g., personal finance application ...
… “works by receiving money or paying out money, in any order, controlled through a user interface”.
2. Decompose into the required components.
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 look for high cohesion & low coupling e.g., personal finance application ...
… decomposes into Assets, Sources, Suppliers, & Interface.
3. Repeat this process for the components.
4. Consider using Façade for each package.
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SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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System structuring
The system is decomposed into several principal sub-systems and communications between these sub-systems are identified
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Control modelling
A model of the control relationships between the different parts of the system is established
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Modular decomposition
The identified sub-systems are decomposed into modules
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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Stakeholder communication
Architecture may be used as a focus of discussion by system stakeholders
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Large-scale reuse
The architecture may be reusable across a range of systems
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System analysis
Means that analysis of whether the system can meet its nonfunctional requirements is possible
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Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
A Classification of Software Architectures
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Garlan & Shaw classification
Data Flow
Independent Components
Virtual Machines
Repositories
Layered
14.3.4
We classify architectures so as to use them for several applications.
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

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Data Flow
Data flowing between functional elements
VM
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Repository Layered
14.3.4.1
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Functional transformations process their inputs to produce outputs
May be referred to as a pipe and filter model (as in UNIX shell)
Variants of this approach are very common. When transformations are sequential, this is a batch sequential model which is extensively used in data processing systems
Not really suitable for interactive systems
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
Example of Data Flow Architecture and Corresponding Class Model
Requirement: Maintain wired financial transactions. account data account data deposit transaction result
Bank data account data deposit data analyze transaction transaction record
Architecture
(data flow)
Log
Comm withdrawal data transaction result bank address withdraw account data
A Class model:
Bank
1
Transaction analyze() record() *
Account withdraw() deposit()
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Communicating processes executing in parallel occasionally communicating
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Client-Server architectures:
Distributed system model which shows how data and processing is distributed across a range of components
Set of stand-alone servers which provide specific services such as printing, data management, etc.
Set of clients which call on these services
Network which allows clients to access servers
The Observer design pattern is of potential use in independent component architectures
14.3.4.2
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
Independent component architecture: an example, film and picture library
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Client 1 Client 2 Client 3 Client 4
Wide-bandwidth network
Catalogue server
Catalogue
Video server
Film clip files
Software Engineering by Sommerville, 2004
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser
Picture server
Digitiz ed photographs
Hypertext server
Hypertext web

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
Independent component architecture: characteristics
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Advantages
Makes effective use of networked systems. May require cheaper hardware
Easy to add new servers or upgrade existing servers
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Disadvantages
No shared data model so sub-systems use different data organisation, data interchange may be inefficient
Redundant management in each server
No central register of names and services - it may be hard to find out what servers and services are available
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Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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A family of applications that are all expressible with a special-purpose high-level language
14.3.4.3
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Interpreter + program in special-purpose language
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Robotic control applications
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The Interpreter design pattern is useful in implementing this architecture.
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Introduction Deployment Arch SW Architecture DataFlow Independent VM
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Primarily built around large data collection
Repository Layered
14.3.4.4
App 1
App 2 database
App 3
Applications mostly storage,retrievals, and querying.
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Sub-systems must exchange data. This may be done in two ways:
Shared data is held in a central database or repository and may be accessed by all sub-systems
Each sub-system maintains its own database and passes data explicitly to other sub-systems
When large amounts of data are to be shared, the repository model of sharing is most commonly used
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Introduction Deployment Arch SW Architecture DataFlow Independent VM
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Subsystems each depending one-way on another subsystem
An architectural layer is a coherent collection of software artifacts
Each layer uses other layers and is used by other layers
Building applications layer by layer can greatly simplify the implementation process
Sometimes the Template design pattern can be applied.
Repository Layered
14.3.4.5
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent
Layered Architecture
3D engine layer
VM Repository Layered
«uses»
Role-playing game layer
Characters RolePlayingGame . . . .
«uses»
Layout
Application layer
Encounter
Characters
Encounter
Environment
. . . .
Encounter Game
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SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent
Requirement: Print monthly statements
VM Repository Layered
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Layered Architecture
Example Using Aggregation
Architecture:
“uses”
Accounts Layer
Vendor-supplied Layer
Ajax bank common library Layer
Ajax bank printing Layer
Class model:
(relationships within packages and Vendor-supplied layer not shown)
Accounts
Account Customer
Ajax bank common library
AjaxLogo AjaxDisclaimer Regulations
Ajax bank printing
Printer Page
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser
Formatter

Introduction Deployment Arch SW Architecture DataFlow Independent
Coad-Yourdon Use of Packages
VM Repository Layered
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Problem domain package
Interface package
Data management package
Task management package
Figure 14.25: Coad-Yourdon Use of Packages
Example
Java.applet
Java.awt
Java.lang
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent VM Repository Layered
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Control models: concerned with the control flow between sub-systems.
Centralised control: one sub-system has overall responsibility for control and starts and stops other sub-systems.
 Example: Call-return model
Routine 1
Main program
Routine 2 Routine 3
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Routine 1.1
Routine 1.2
Routine 3.1
Routine 3.2
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Event-based control: each sub-system can respond to externally generated events from other sub-systems or the system’s environment
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Example: Broadcast model
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser

Introduction Deployment Arch SW Architecture DataFlow Independent
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What is a software architecture?
Architecture is a high-level design
VM Repository Layered
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Complexity
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Cohesion: is the degree to which communication takes place among the module’s elements (High cohesion is better)
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Coupling: is the degree to which modules depend directly on other modules (Low coupling is better)
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Classification of Software Architectures
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VM Repository Layered
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14.4
SWE 316: Software Design and Architecture – Dr. Khalid Aljasser