04 Software Architecture

Question 1

what is stakeholder communication

Answer 1

discuss system without confusing details

Question 2

software architecture components

Answer 2

identify structure of software system with a set of interacting components and design guiding principles

Question 3

what is project planning

Answer 3

high level architecture view

Question 4

what is large scale resue

Answer 4

architecture tat may be reusable across a range of systems

Question 5

why is software architecture important

Answer 5

1. affects performance, robustness, distributability and maintainability
2. show how system is organised and how components interoperate
3. refactoring system architecture is expensive as many components will be affected

Question 6

architecture decision factors

Answer 6

1. non functional characteristics
   - affects all users
2. product lifetime
   - long life = need architecture to be evolvable
3. software reuse
   - save time/effort but may constrain architectural choices
4. number of users
   - support quick scale and down to prevent performance degrade
5. software compatibility
   - adopt products in different system limit architectural choices

Question 7

types of software architectural patterns

Answer 7

1. model view controller MVC
2. layered
3. repository
4. client server
5. peer to peer
6. pipe and filter
7. plugin

Question 8

model view controller MVC pattern

Answer 8

divides system into 3 components

model: data store
view: data representation
controller: server

user use controller
controller manipulate model
model updates view
user sees updated view

Question 9

when should we choose MVC pattern

Answer 9

1. when multiple ways to view and interact with data are needed.
2. when future requirements for interactions are unknown

Question 10

MVC pattern advantages and disadvantages

Answer 10

advantages

• allow data to change independently of its representation and vice versa
• present data in different ways

disadvantages
- may involve additional code and complexity

Question 11

layered pattern

Answer 11

1. organises system into layers with associated functions each
2. layer only provides services to layer above it
3. lowest layer is the core service
4. when a layer changes, only adjacent layers affected

Question 12

when should layered pattern be used

Answer 12

1. when building new facilities on top of existing systems

2. development spread across multiple team responsible for a layer each

Question 13

layered pattern advantages and disadvantages

Answer 13

advantages

• able to replace entire layer with interface maintained
• redundant facilities provide at each layer

disadvantages
- clean separation of layers is difficult

Question 14

repository pattern

Answer 14

large amount of shared data held in central database that can be accessed by all subsystems

components only communicate with the repository

Question 15

when should repository pattern be used

Answer 15

1. large volume of data generated and stored for a long time

2. when inclusion of data in repository triggers actions in data-driven system

Question 16

repository pattern advantages and disadvantages

Answer 16

advantages

• no need to know the existence of other components
• all data is consistent

disadvantages

• failure in repository affects entire system
• inefficient communication
• distributing central repository across several PC is difficult

Question 17

client server pattern

Answer 17

functionality organised as services which may be stored in different servers

clients access servers for services

Question 18

when should client server pattern be used

Answer 18

data is stored in database and is accessed from different location

Question 19

client server pattern advantages and disadvantages

Answer 19

advantages

• servers can be distributed across network
• easy to add or upgrade servers

disadvantages

• susceptible to attacks
• performance is unpredictable and depends on network
• difficult to manage if servers are owned by different organisations

Question 20

peer to peer pattern

Answer 20

peer act as client and server

responsibility for hosting and managing services are shared amongst clients

Question 21

when should peer to peer pattern be used

Answer 21

need computational power but constrained by hardware capabilities

Question 22

peer to peer pattern advantages and disadvantages

Answer 22

advantages

• decentralised
• reliable
• failure of 1 peer does not affect others

disadvantages

• how to look for other peers offering the same services
• unsure is peers are trustable

Question 23

pipe and filter pattern

Answer 23

data processed and then used

Question 24

pipe and filter pattern advantages and disadvantages

Answer 24

advantages

• easy to understand
• supports transformation reuse
• easy to add transformations

disadvantages

• long system overhead
• cannot reuse with incompatible data

Question 25

plugin (microkernel) pattern

Answer 25

flexible for users to extend their own functionality | core systems is always present

Question 26

when should plugin pattern be used

Answer 26

need easy extension of more functionalities | need additional features to be added in later

Question 27

when should plugin pattern be used

Answer 27

need easy extension of more functionalities | need additional features to be added in later

Question 28

plugin pattern advantages and disadvantages

Answer 28

advantages - app remains small - customisable, small, easily added disadvantages - difficult to decide what to put into the micokernel - too many plugin slows down application - slow testing