Design Methodology

Question 1

The Design Problem

Answer 1

Small amount of developers but a large requirement specification.

Question 2

Stages of Design

Answer 2

Problem understanding -> look at the problem from different angles to discover design requirements.
Identify one of more solutions.
Describe solution abstractions -. use graphical formal or other notions to describe design’s components.
Repeat process for each identified abstraction until design is expressed in primitive terms.

Question 3

Phases in Design Process

Answer 3

• architectural design
• abstract specification
• interface design
• component design
• data structure
• algorithm design

Question 4

Architectural Design

Answer 4

Identify sub-systems.

Question 5

Abstract Specification

Answer 5

Specify sub-systems.

Question 6

Interface Design

Answer 6

Describe sub-system interfaces.

Question 7

Component Design

Answer 7

Decompose sub-systems into components.

Question 8

Data Structure

Answer 8

Design data structures to hold problem data.

Question 9

Algorithm Design

Answer 9

Design algorithms for problem functions.

Question 10

Computer system, modular or monolithic?

Answer 10

Modularity, like subroutines, are more cheaper and efficient and therefore are used for computer systems.

Question 11

Objectives for defining system modules.

Answer 11

Identify what they are, what they should know and how modules interact with one another.

Question 12

Modularity Requirements

Answer 12

The modules must be:
- Autonomous -> can work by itself.
- Coherent - strength of the correlation of the elements inside the module.
- Robust - can cope with errors.

Question 13

High Cohesion

Answer 13

Elements inside module work together well.

Question 14

Low Coupling

Answer 14

High interdependence between modules.

Question 15

Functional Decomposition

Answer 15

Leads to procedural abstraction.

Question 16

Procedural Abstraction

Answer 16

Procedures represent distinct logical functions in a program.

Question 17

Object Orientated Design

Answer 17

A collection of interacting objects, with the system state being decentralised and each object manages its own state.

Question 18

Five Criteria in evaluating modular design methods.

Answer 18

• Modular decomposition
• Modular composability
• Modular understandability
• Modular continuity
• Modular protection

Question 19

Modular Decomposition

Answer 19

Design method supports the decomposition of a problem into smaller problems.

Question 20

Modular Composability

Answer 20

A design method which creates modules that may be freely combined to create new systems.

Question 21

Modular Understandability

Answer 21

A design method which encourages easily understandable modules.

Question 22

Modular Continuity

Answer 22

Can be updated without effecting the whole system (only one or a small amount of modules).

Question 23

Modular Protection

Answer 23

Yields architecture in which abnormal conditions at run-time only effect one or a small amount of modules.

Question 24

Repository Model

Answer 24

All shared data is held in central database which may be accessed by all sub-systems.

Question 25

Advantages and disadvantages of repository models.

Answer 25

Databases are efficient in sharing large amounts of data. The model is also visible through repository schema. Requires agreement and limited evolution.

Question 26

Good system properties

Answer 26

- useful and usable - reliable (low coupling) - flexible (low coupling, high cohesion) - affordable (reusable software) - available (decreased development time through reuse)

Question 27

Interface

Answer 27

Defines some features of a module which upon other parts of the system may rely, and is known as an abstraction of the module.

Question 28

Encapsulation

Answer 28

An encapsulation of a module means that users of said module cannot know more about the module than what is given by the interface.

Question 29

Good Interface Design Principals

Answer 29

- linguistic modular units - few interfaces - small interfaces - explicit interfaces - information hiding

Question 30

Linguistic Modular Units

Answer 30

Modules must correspond to linguistic units in the programming language used.

Question 31

Few Interfaces

Answer 31

Overall communication between modules should be minimal, and every module should communicate with others as little as possible.

Question 32

Small Interfaces (loose coupling)

Answer 32

Implies that if any two modules communicate, they exchange as little information as possible.

Question 33

Explicit Interfaces

Answer 33

Communication between modules should be traceable.

Question 34

Information Hiding

Answer 34

All information about a module should be private to the module unless it is specifically declared otherwise.

Question 35

Tight coupling v loose coupling

Answer 35

Tight coupling is the overuse of shared variables and control information exchange. In other words, modules communicate too much, compared to loose coupling, which allows component changes to not affect other modules due to lack of communication between modules.

Question 36

Cohesion Levels

Answer 36

- coincidental cohesion (weak) - logical association (weak) - temporal cohesion (weak) - communication cohesion (medium) - sequential cohesion (medium) - functional cohesion (strong) - object cohesion (strong)

Question 37

Coincidental Cohesion

Answer 37

Parts of a component are simply bundled together.

Question 38

Logical Association

Answer 38

Components which perform similar functions are grouped.

Question 39

Temporal Cohesion

Answer 39

Components which are activated at the same time are grouped.

Question 40

Communicational Cohesion

Answer 40

All elements of a component operate on the same input or produce the same output

Question 41

Sequential Cohesion

Answer 41

The output for one part of the component is the input to another part.

Question 42

Functional Cohesion

Answer 42

Each part of a component is necessary for the execution of a single function.

Question 43

Object Cohesion

Answer 43

Each operation provides functionality which allows objects attributes to be modified or inspected.

Question 44

Cohesion with inheritance

Answer 44

Inheriting attributes from super-classes weakens cohesion since it allows communication.

Question 45

Cohesion v Encapsulation

Answer 45

Cohesion is the measure of abstraction that means developers do not need to concern themselves with the internal working of a module. Encapsulation means that developers are unable to use hidden information within a module, ensuring that subtle errors cannot be introduced when using connected modules.

Question 46

High cohesion, low coupling and well defined interfaces.

Answer 46

The combination of these three can lead to reusability of modules in other systems.