1. Lecture 9 Architectures and Frameworks
SWE 316: Software Design and Architecture
Lecture 9 Architectures and Frameworks
To understand
… the goals of software architecture
… the meaning of “frameworks”
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.

2. Process Phases Discussed in This Chapter
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Requirements
Analysis
Process Phases Discussed in This Chapter
Design
Framework
Architecture
Detailed Design
Implementation
Key: x
= main emphasis x
= secondary emphasis
Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

3. The meaning of software architecture
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The meaning of software architecture
14.1
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

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The meaning of software architecture
Architectural Design:
Establishing the overall structure of a software system
The design process for identifying the sub-systems making up a system and the framework for sub- system control and communication is architectural design
The output of this design process is a description of the software architecture

5. Software architecture
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Software architecture
If the application is small (e.g. 10 classes) this decomposition may be considered as architecture.
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)
Framework: a collection of classes applicable to multiple applications

6. An Architecture for a Video Store Application
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An Architecture for a Video Store Application
Videos
Rentals
Customers
Architecture is a high-level design

7. A Sequence for Obtaining The Class Model
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A Sequence for Obtaining The Class Model
0. Framework (some or all pre-existing)
More
general
2. Create architecture
-- typically use framework
3. Create remaining
design classes
-- to complete the class model
-- possibly use framework
1. Create domain classes
-- from requirements analysis

8. Models of OO Analysis and Design
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Models of OO Analysis and Design
14.2
To express requirements, architecture & detailed design
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 …
State model
“reacting to these events ...”
e.g., when foreign character enters
* Video game example

9. Deployment Environment
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Deployment Environment
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
Reliability
Security
Performance
Usability
Supportability
Object-Oriented Analysis and Design with the Unified Process

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Software Architecture
14.3
Design goals (review)
Correctness
Sufficiency
Robustness
Flexibility
Reusability
Efficiency
Can be handled at lower levels of design

11. Modularization, cohesion, and coupling
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Modularization, cohesion, and coupling
It is not hard to write small programs
However, large applications are difficult to create
The principal problem  complexity
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
14.3.2
Design Goal : Correctness/Modularity
We want to decompose designs into modules, each well-knit, and depending on few others.

12. Modularization, Cohesion, and Coupling
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Modularization, Cohesion, and Coupling
Goals of software decomposition: Cohesion & Coupling
Cohesion within a module is the degree to which communication takes place among the module’s elements
Coupling is the degree to which modules depend directly on other modules
Effective modularization is accomplished by
maximizing cohesion and
minimizing coupling

13.  Cohesion and Coupling  Fig 14.16 High cohesion Low coupling
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Cohesion and Coupling
Fig 14.16 1 2 3 4 5 6
High cohesion
Low coupling
High coupling
Bridge
component  
Steel
truss

14. Using Façade Pattern 14/33 SW Architecture Introduction
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Using Façade Pattern

15. Architecture and Modularization of Encounter Video Game
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Architecture and Modularization of Encounter Video Game
EncounterGame
EncounterGame
«facade»
EncounterCharacters
EncounterCast
«facade»
EncounterEnvironment
EncounterEnvironment
«facade»

16. Figure 14.19 Selecting a Basic Architecture
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Figure Selecting a Basic Architecture
1. Develop a mental model of the application.
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.
look for high cohesion & low coupling
… decomposes into Assets, Sources, Suppliers, & Interface.
3. Repeat this process for the components.
4. Consider using Façade for each package.

17. Architectural design process
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Architectural design process
System structuring
The system is decomposed into several principal sub-systems and communications between these sub-systems are identified
Control modelling
A model of the control relationships between the different parts of the system is established
Modular decomposition
The identified sub-systems are decomposed into modules

18. Advantages of explicit architecture
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Advantages of explicit architecture
Stakeholder communication
Architecture may be used as a focus of discussion by system stakeholders
Large-scale reuse
The architecture may be reusable across a range of systems
System analysis
Means that analysis of whether the system can meet its non- functional requirements is possible

19. A Classification of Software Architectures
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A Classification of Software Architectures
14.3.4
Garlan & Shaw classification
Data Flow
Independent Components
Virtual Machines
Repositories
Layered
Reusability
We classify architectures so as to use them for several applications.

20. 1- Data Flow architecture
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1- Data Flow architecture
Data Flow
Data flowing between functional elements
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

21. Example of Data Flow Architecture and Corresponding Class Model
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Example of Data Flow Architecture and Corresponding Class Model
Requirement: Maintain wired financial transactions.
bank address
account data
Bank
data
record
Log
transaction
analyze
deposit
deposit data
withdrawal data
result
Architecture
(data flow)
Comm
withdraw
A Class model:
Bank
Account
withdraw()
deposit() * 1
Transaction
analyze()
record()

22. 2- Independent component architecture
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2- Independent component architecture
Communicating processes
executing in parallel
occasionally communicating
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

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Independent component architecture: an example, film and picture library
Software Engineering by Sommerville, 2004

24. Independent component architecture: characteristics
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Independent component architecture: characteristics
Advantages
Makes effective use of networked systems. May require cheaper hardware
Easy to add new servers or upgrade existing servers
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

25. 4- Virtual machine architectures
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4- Virtual machine architectures
A family of applications that are all expressible with a special-purpose high-level language
Interpreter + program in special-purpose language
Robotic control applications
The Interpreter design pattern is useful in implementing this architecture.

26. 4- Repository architecture
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4- Repository architecture
Primarily built around large data collection
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
App 1
database
App 3
App 2
Applications mostly storage,retrievals, and querying.

27. 5- Layered architecture
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5- Layered architecture
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.

28. Layered Architecture 3D engine layer «uses» Role-playing game layer
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Layered Architecture
3D engine layer
«uses»
Role-playing game layer
Characters
RolePlayingGame
Layout
«uses»
Application layer
Encounter
Characters
Encounter
Environment
Encounter Game

29. Layered Architecture Example Using Aggregation
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Layered Architecture Example Using Aggregation
Requirement: Print monthly statements
Architecture:
Vendor-supplied Layer
Accounts Layer
Ajax bank common library Layer
“uses”
Ajax bank printing Layer
Class model: (relationships within packages and Vendor-supplied layer not shown)
Accounts
Ajax bank common library
Account
Customer
AjaxLogo
AjaxDisclaimer
Regulations
Ajax bank printing
Printer
Page
Formatter

30. Coad-Yourdon Use of Packages
First reading
6.1 Organize into Subsystems
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Coad-Yourdon Use of Packages
Example
Problem domain package
Interface package
Data management package
Task management package
Figure 14.25: Coad-Yourdon Use of Packages
Java.applet
Java.awt
Java.lang

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Other architectures
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
Event-based control: each sub-system can respond to externally generated events from other sub-systems or the system’s environment
Example: Broadcast model

32. Summary What is a software architecture? Complexity
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Summary
What is a software architecture?
Architecture is a high-level design
Complexity
Cohesion: is the degree to which communication takes place among the module’s elements (High cohesion is better)
Coupling: is the degree to which modules depend directly on other modules (Low coupling is better)
Classification of Software Architectures

33. 14.4 Framework Next Lecture 33/33 Introduction Deployment Arch
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Framework
14.4