Software Design Architecture Answers

Software Design Architecture Answers

1. a.i) Compliment between software architecture and software design.

Software Architecture focuses more on the interaction between the externally visible components of the system where as the Design is about how the internal components of the system interact with each other. Software Architecture is more about what we want the system to do and Software Design is about how we want to achieve that. Software Architecture is at a higher level of abstraction than the Software Design. Software Architecture is concerned with issues beyond the data structures and algorithms used in the system.

Software Architecture shows how the different modules of the system communicate with each other and other systems. What language is to be used? What kind of data storage is present, what recovery systems are in place? Like design patterns there are architectural patterns. Such MVC, 3-tier layered design, etc.

Software design is about designing the individual modules / components. What are the responsibilities, functions, of module x or class Y? What can it do, and what not? What design patterns can be used? UML diagram/flow chart/simple wireframes (for UI) for a specific module/part of the system.

Software Architecture is the design of the entire system, while Software Design emphasizes on a specific module / component / class level.

All architecture is design but not all design is architecture.

Software Architecture is “what” we are building. Software Design is “how” we are building.

ii) 3 advantages of using Philippe Kruchten architecture view model for software architecture

Stakeholder communication – architecture may be used as focus of discussion by system stakeholders

System analysis – means that analysis of whether the system can meet its nonfunctional requirements is possible.

Large-scale reuse – the architecture may be reusable across range of systems.

b) Why tactics is important for software architecture

Architect uses tactics as early design decision to fulfill quality attributes

The choice of tactics are based on qualities attributes scenario analysis  Tactics are implemented using patterns which are the solutions of recurring problems.

C i) The goal of availability tactics

Prevention – to keep faults from becoming failures

Detection – to detect faults

Recovery – to make possible recovery

C ii) example of availability tactics mechanisms and implications

Heartbeat: A fault detection mechanism that employs a periodic message exchange between a system monitor and a process being monitored.

• Comp. 1 emits a “heartbeat” message periodically

• Comp. 2 listens for it

• If heartbeat fails

Comp. 1 assumed failed

Fault correcting comp. 3 is notified

Heartbeat can also carry data

d) Modifiability tactics that can be used to control time and cost in making modifications to the system. 

Modifiability deals with change and the cost in time or money of making a change.

• To which extent this modification affects other functions or quality attributes.

Tactics to reduce the cost of making a change include

• making modules smaller,

• increasing cohesion, and

• reducing coupling.

• Deferring binding will also reduce the cost of making a change.

2a) 2 software design scenarios that demonstrate the benefits of architecture styles.

Design reuse – well understood solution applied to new problems

Understanding of the system organization – a phase such as client-server conveys a lot of information.

b) Benefits of using long-term and short term patterns in software architecture

Short terms benefits

·         Promote reuse

·         Prevent repeat similar mistakes  Implement a common desire vocabulary

·         Provides a clear procedure for implementation  Shorten desire phase

Long terms benefits        

·         Provide a clear structure for maintenance programs to help understand the code.

·         Use whenever extensibility procedures are available in the patterns

C i) Layered style

  ii) Advantages - increasing the abstraction level

 iii) Disadvantages - performance

2 d i) compare cohesion to coupling in software structural design 

cohesion coupling Indicate the relationship within the module Indicate the relationship between modules Show the module relative functional strength  Show the relative independence among the modules Degree which a component module focus in the single thing Degree which a component module is connected to other modules.

ii) Level of cohesion and coupling for subsystems

Coupling -- the strength of dependencies between two subsystems o strongly coupled == changes to one subsystem likely to affect the other o loosely coupled == relatively independent (as long as the interface doesn't change) 

o Goal: Strive for loose couplings. Don't share attributes; use operations and a well-specified interface 

 cohesion / coherence -- strength of dependencies within a subsystem o High cohesion: subsystem contains related objects performing similar tasks o Low cohesion: subsystem contains a number of unrelated objects

 o Goal: Strive for high cohesion

3. a i) 2 advantages of object composition over class inheritance

Eliminates excessive use of subclass 

Allow changes in object behavior in runtime

ii) Interface over implementation 

Interface simulates multiple inheritances. All classes in java must have one based class. Multiple inheritance of a class is not allowed. However a java class/interface may implement or extend any number of interfaces

3. b. I and 3.b. ii)

  c. i) creational design patterns – abstract factor pattern because hide how instances classes and methods work together to provide set of services.

 ii) Structural design patterns – adapter pattern because it allow to wrap an interface of existing class to be used as another interface

4. a.i) WMC is determined by count the number of methods in a specific class.

ii) WMC Copyitem = 4

iii) WMC Loan = 2

iv) the significance of part

 4 a.ii) Is that we determined the WMC of class copyitem  by giving us 4 which represents the number of methods in the class copyitem. While in the of part 4a. iii. Is that we determined the WMC of class Loan by giving us 2 which represents the number of methods in the class Loan.

4b.i) DIT is is determined by count the number of levels of superclass from which it inherits methods.

ii) DIT Holding =0

iii) DIT Record Material =2

iv) the DIT of part 4 b.iii. has high reusability and complexity because is in between the DIT range which is 2-6.

c.i) keep the CBO for each class as low as possible to reduce coupling

4 c.ii) MPC

CBO borrower = 1

CBO Loan =1

RFC borrower = 3

RFC Loan =3

 5bi) 

Source	Adam
Stimulus	registered
Artefact	Uberia
Response	Publish to potential customers
Response	measure maximum 10 seconds

5 b.ii)

Source	Eve
Stimulus	Make request
Artefact	Uberia
Response	Inform the customer
Response measure	maximum 30 seconds