Question 1

System Design

Accepted Answer

◦  Decomposing the System
◦  Addressing Design Goals

Question 2

There are two ways of constructing a software design, Sir Antony Hoare

Accepted Answer

–  One way is to make it so simple that there are obviously no deficiencies
–  The other way is to make it so complicated that there are no obvious deficiencies.

Question 3

What is Architecture

Accepted Answer

The highest-level breakdown of a system into its parts; the decisions that are hard to change; what is architecturally significant can change over a system's lifetime; and, in the end, architecture boils down to whatever the important stuff is. Fowler

Question 4

System architect

Accepted Answer

1) Handles the definition of the overall system and the sub-
 systems
2) External Architect

Question 5

Object designer

Accepted Answer

◦  Handles the sub-system’s interfaces and the internal
structures of the sub-systems
◦  Internal architect

Question 6

Implementer

Accepted Answer

◦  Handles classes inside the sub-system

Question 7

System Design Is

Accepted Answer

◦  Define the design goals of the project
◦  Decompose the system into smaller subsystems that can be realized by
individual teams
◦  Select strategies for building the system

Question 8

Select strategies for building the system

Accepted Answer

"  Hardware/software strategy
"  Persistent data management strategy
"  Global control flow strategy
"  Access control policy
"  Boundary conditions handling

Question 9

The result of system design

Accepted Answer

is a model that includes a subsystem decomposition and a clear description of each of the mentioned strategies

Question 10

Analysis results in the requirements model products

Accepted Answer

◦  Nonfunctional requirements and constraints
◦  Use case model
◦  Object model
◦  Sequence diagram

Question 11

System design results in the products

Accepted Answer

◦  Design goals
◦  Software architecture
◦  Boundary use cases

Question 12

Object Design

Accepted Answer

”specifying the boundaries between objects”
"  Interfaces are defined in details

Question 13

Design Goal Examples

Accepted Answer

•  Response time
•  Throughput
•  Robustness
•  Reliability
•  Availability
•  Scalability
•  Fault tolerance
•  Security
•  Extensibility
•  Modifiability
•  Portability
•  Recoverability
•  Traceability •  Utility
•  Usability

Question 14

System Design Concepts

Accepted Answer

subsystem, service, coupling, cohesion, layering, partitioning

Question 15

Subsystem

Accepted Answer

a subsystem is a replaceable part of the system with well-defined interfaces that encapsulate the state and behavior of it contained classes

Question 16

subsystem decomposition

Accepted Answer

The division of the system into subsystems. Each subsystem is described in terms of its services during system design and its API during object design. Subsystem decomposition is part of the system design model.

Question 17

Component Diagram

Accepted Answer

In the Unified Modeling Language, a component diagram depicts how components are wired together to form larger components and or software systems. They are used to illustrate the structure of arbitrarily complex systems.

Question 18

Partitions

Accepted Answer

Partitions vertically divide a system into several independent (or weakly- coupled) subsystems that provide services on the same level of abstraction.

Question 19

Layers

Accepted Answer

A layer is a subsystem that provides subsystem services to a higher layers (level of abstraction)

Question 20

Subsystem Heuristics (Abbott’s)

Accepted Answer

◦  Assign objects in one use case to the same subsystem
◦  dedicated subsystem for objects used for moving data among subsystems
◦  Minimize the number of associations crossing subsystems boundaries
◦  All objects in same subsystem funtionally related

Question 21

Client/Server Architecture

Accepted Answer

1) Users interact only with the client
2) Client knows the interface of the server (its service)

Question 22

MVC Architecture

Accepted Answer

"attach multiple views to a model to provide different presentations" (view/model decoupling)
"change the way a view responds to user input without changing its visual presentation" (view/controller decoupling)

Question 23

3-tier Architecture

Accepted Answer

a hierarchy of 3 layers usually called presentation, application and data layer

Question 24

n-tier Architecture

Accepted Answer

for example 4 tier has the interface broken down to 2 parts

Question 25

Peer-to-Peer Architecture

Accepted Answer

computing or networking is a distributed application architecture that partitions tasks or work loads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes.

Question 26

Component-Based Architecture

Accepted Answer

is a branch of software engineering that emphasizes the separation of concerns in respect of the wide-ranging functionality available throughout a given software system.

Question 27

Event-driven architecture

Accepted Answer

is a software architecture pattern promoting the production, detection, consumption of, and reaction to events.

Question 28

Communication Subsystem

Accepted Answer

provides services for managing connections and functions.

Question 29

System Design Activities

Accepted Answer

1) Map subsystems to hardware/software platforms
2) Manage persistent data
3) Define access control policies
4) Select Global control flow
5) Describe boundary conditions

Question 30

Mapping Subsystems to Hardware

Accepted Answer

◦  How shall we realize the subsystems: Hardware or Software?
◦  How is the object model mapped on the chosen hardware & software? ◦  Mapping Objects onto Reality: Processor, Memory, Input/Output
◦  Mapping Associations onto Reality: Connectivity

Question 31

Processor issues

Accepted Answer

◦  Is the computation rate too demanding for a single processor?
◦  Can we get a speedup by distributing tasks across several processors? ◦  How many processors are required to maintain steady state load?

Question 32

Memory issues

Accepted Answer

◦  Is there enough memory to buffer bursts of requests?

Question 33

I/O issues

Accepted Answer

◦  Do you need an extra piece of hardware to handle the data
generation rate?
◦  Does the response time exceed the available communication bandwidth between subsystems or a task and a piece of hardware?

Question 34

Designing Global Control Flow

Accepted Answer

1) Choose implicit control 
2) Choose explicit control

Question 35

Implicit Control  (non-procedural, declarative languages)

Accepted Answer

1) Logic programming
2) Rule-based systems

Question 36

Explicit Control (procedural languages)

Accepted Answer

1) Centralized
2) Decentralized

Question 37

Centralized control

Accepted Answer

1) Procedure-driven 
2) event- driven

Question 38

Procedure-driven control

Accepted Answer

◦  Control resides within program code. Example:
Main program calling procedures of subsystems. ◦  Simple, easy to build
◦  hard to maintain

Question 39

Event-driven control

Accepted Answer

◦  Control resides within a dispatcher calling
functions via callbacks.
◦  Very flexible, good for the design of graphical user interfaces, easy to extend
◦  Difficult to control overall flow

Question 40

Identification of Services

Accepted Answer

"  Name the services meaningful
"  An interface specification of a subsystem defines the role the
subsystem plays in cooperation with a specific other subsystem "  NOT (operations and attributes)

Question 41

Boundary Conditions

Accepted Answer

1) Initialization
2) Termination
3) Failure
Create use cased for the user administrator to take care all user non-accounted administration tasks

Question 42

Initialization

Accepted Answer

The system is brought from a non-initialized state
to steady-state

Question 43

Termination

Accepted Answer

Resources are cleaned up and other systems are
notified upon termination

Question 44

Failure

Accepted Answer

Possible failures: Bugs, errors, external problems
Good system design foresees fatal failures and provides mechanisms to deal with them.

Question 45

Quality assurance of System Design

Accepted Answer

1) First: Does the System Design follow the design goals?
2) Correct, Complete, Consistent, Realistic, Readable

Question 46

Sound Documentation

Accepted Answer

from the Reader’sPointofView
 !  AvoidUnnecessaryRepetition
!  AvoidAmbiguity
!  ExplainYourNotation
!  Use a Standard Organization
!  Record Rationale
!  Keep Documentation Current but Not Too Current !  Review Documentation for Fitness of Purpose

Question 47

ATAM

Accepted Answer

ArchitectureTradeoffAnalysisMethod:
1)identified risks early in the life cycle
2)increased communication among stakeholders
3)clarified quality attribute requirements
4)improved architectureDocumentation
5)documented basis for architectural decisions

Question 48

CBAM

Accepted Answer

Cost Benefit Analysis Method
The CBAM enables users to make informed decisions about software requirements and software investments based on an analysis of the economic and architectural implications of those decisions.

8) Design

Large System Development

Question	Answer
System Design	◦ Decomposing the System ◦ Addressing Design Goals
There are two ways of constructing a software design, Sir Antony Hoare	– One way is to make it so simple that there are obviously no deficiencies – The other way is to make it so complicated that there are no obvious deficiencies.
What is Architecture	The highest-level breakdown of a system into its parts; the decisions that are hard to change; what is architecturally significant can change over a system's lifetime; and, in the end, architecture boils down to whatever the important stuff is. Fowler
System architect	1) Handles the definition of the overall system and the sub- systems 2) External Architect
Object designer	◦ Handles the sub-system’s interfaces and the internal structures of the sub-systems ◦ Internal architect
Implementer	◦ Handles classes inside the sub-system
System Design Is	◦ Define the design goals of the project ◦ Decompose the system into smaller subsystems that can be realized by individual teams ◦ Select strategies for building the system
Select strategies for building the system	" Hardware/software strategy " Persistent data management strategy " Global control flow strategy " Access control policy " Boundary conditions handling
The result of system design	is a model that includes a subsystem decomposition and a clear description of each of the mentioned strategies
Analysis results in the requirements model products	◦ Nonfunctional requirements and constraints ◦ Use case model ◦ Object model ◦ Sequence diagram
System design results in the products	◦ Design goals ◦ Software architecture ◦ Boundary use cases
Object Design	”specifying the boundaries between objects” " Interfaces are defined in details
Design Goal Examples	• Response time • Throughput • Robustness • Reliability • Availability • Scalability • Fault tolerance • Security • Extensibility • Modifiability • Portability • Recoverability • Traceability • Utility • Usability
System Design Concepts	subsystem, service, coupling, cohesion, layering, partitioning
Subsystem	a subsystem is a replaceable part of the system with well-defined interfaces that encapsulate the state and behavior of it contained classes
subsystem decomposition	The division of the system into subsystems. Each subsystem is described in terms of its services during system design and its API during object design. Subsystem decomposition is part of the system design model.
Component Diagram	In the Unified Modeling Language, a component diagram depicts how components are wired together to form larger components and or software systems. They are used to illustrate the structure of arbitrarily complex systems.
Partitions	Partitions vertically divide a system into several independent (or weakly- coupled) subsystems that provide services on the same level of abstraction.
Layers	A layer is a subsystem that provides subsystem services to a higher layers (level of abstraction)
Subsystem Heuristics (Abbott’s)	◦ Assign objects in one use case to the same subsystem ◦ dedicated subsystem for objects used for moving data among subsystems ◦ Minimize the number of associations crossing subsystems boundaries ◦ All objects in same subsystem funtionally related
Client/Server Architecture	1) Users interact only with the client 2) Client knows the interface of the server (its service)
MVC Architecture	"attach multiple views to a model to provide different presentations" (view/model decoupling) "change the way a view responds to user input without changing its visual presentation" (view/controller decoupling)
3-tier Architecture	a hierarchy of 3 layers usually called presentation, application and data layer
n-tier Architecture	for example 4 tier has the interface broken down to 2 parts
Peer-to-Peer Architecture	computing or networking is a distributed application architecture that partitions tasks or work loads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes.
Component-Based Architecture	is a branch of software engineering that emphasizes the separation of concerns in respect of the wide-ranging functionality available throughout a given software system.
Event-driven architecture	is a software architecture pattern promoting the production, detection, consumption of, and reaction to events.
Communication Subsystem	provides services for managing connections and functions.
System Design Activities	1) Map subsystems to hardware/software platforms 2) Manage persistent data 3) Define access control policies 4) Select Global control flow 5) Describe boundary conditions
Mapping Subsystems to Hardware	◦ How shall we realize the subsystems: Hardware or Software? ◦ How is the object model mapped on the chosen hardware & software? ◦ Mapping Objects onto Reality: Processor, Memory, Input/Output ◦ Mapping Associations onto Reality: Connectivity
Processor issues	◦ Is the computation rate too demanding for a single processor? ◦ Can we get a speedup by distributing tasks across several processors? ◦ How many processors are required to maintain steady state load?
Memory issues	◦ Is there enough memory to buffer bursts of requests?
I/O issues	◦ Do you need an extra piece of hardware to handle the data generation rate? ◦ Does the response time exceed the available communication bandwidth between subsystems or a task and a piece of hardware?
Designing Global Control Flow	1) Choose implicit control 2) Choose explicit control
Implicit Control (non-procedural, declarative languages)	1) Logic programming 2) Rule-based systems
Explicit Control (procedural languages)	1) Centralized 2) Decentralized
Centralized control	1) Procedure-driven 2) event- driven
Procedure-driven control	◦ Control resides within program code. Example: Main program calling procedures of subsystems. ◦ Simple, easy to build ◦ hard to maintain
Event-driven control	◦ Control resides within a dispatcher calling functions via callbacks. ◦ Very flexible, good for the design of graphical user interfaces, easy to extend ◦ Difficult to control overall flow
Identification of Services	" Name the services meaningful " An interface specification of a subsystem defines the role the subsystem plays in cooperation with a specific other subsystem " NOT (operations and attributes)
Boundary Conditions	1) Initialization 2) Termination 3) Failure Create use cased for the user administrator to take care all user non-accounted administration tasks
Initialization	The system is brought from a non-initialized state to steady-state
Termination	Resources are cleaned up and other systems are notified upon termination
Failure	Possible failures: Bugs, errors, external problems Good system design foresees fatal failures and provides mechanisms to deal with them.
Quality assurance of System Design	1) First: Does the System Design follow the design goals? 2) Correct, Complete, Consistent, Realistic, Readable
Sound Documentation	from the Reader’sPointofView ! AvoidUnnecessaryRepetition ! AvoidAmbiguity ! ExplainYourNotation ! Use a Standard Organization ! Record Rationale ! Keep Documentation Current but Not Too Current ! Review Documentation for Fitness of Purpose
ATAM	ArchitectureTradeoffAnalysisMethod: 1)identified risks early in the life cycle 2)increased communication among stakeholders 3)clarified quality attribute requirements 4)improved architectureDocumentation 5)documented basis for architectural decisions
CBAM	Cost Benefit Analysis Method The CBAM enables users to make informed decisions about software requirements and software investments based on an analysis of the economic and architectural implications of those decisions.

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