Final Material - System Design

Question 1

What is the difference between architectural design and component design?

Answer 1

Architectural design is an abstract version of the system that identifies the software as a system with many components interacting with each other
Component design is more detailed toward modules and implementations. Defines the logical structure of each module and interfaces to communicate with other modules

Question 2

What is an architectural pattern?

Answer 2

A means of representing, sharing, and reusing knowledge. A stylized description of good design practice that has been tried and tested in different environments

Question 3

What is the model view controller architectural pattern?

Answer 3

A model that separates presentation and interaction from system data.
The model component manages system data and operations of the data
The view component defines and manages how data is presented to the user
The controller component manages user interaction and passes interactions to the view and the model

Question 4

When should you use model-view-controller architectural pattern

Answer 4

When there are multiple ways to view and interact with the data
When the future requirements for interaction and presentation of data are unknown

Question 5

What are the advantages and disadvantages of model view controller architectural pattern?

Answer 5

Advantages: allows data to change independently of representation and vice-versa, supports presentation of the same data in different way with changes made in one representation shown in all
Disadvantage: Involves additional code and complexity when data model and interactions are simple

Question 6

What is the layered architecture pattern?

Answer 6

Organizes the system into layers with related functionality for each layer

Question 7

When should you use the layered architectural pattern?

Answer 7

When building new facilities on existing systems
When development is spread across several teams with each team responsible for a layer
When there is a requirement for multi-level security

Question 8

What are the advantages and disadvantages of the layered architectural pattern?

Answer 8

Advantages: allows replacement of entire layers as long as the interface is maintained
Disadvantages: Providing clean separation is difficult and a high-level layer may need to interact with layers not just directly below it, performance can be a problem because of multiple levels of interpretation of a service request

Question 9

What is the client-server architectural pattern?

Answer 9

Functionality of the system is organized into services with each service delivered from a different server

Question 10

When should you use the client-server architectural model?

Answer 10

When data in a shared database needs to be accessed from a range of locations

Question 11

What are the advantages and disadvantages of client-server architectural pattern?

Answer 11

Advantages: Servers can be distributed across a network, general functionality can be available to all clients and does not need to be implemented by all services
Disadvantages: Each service is a single point of failure, performance is unpredictable because it depends on the network and the system

Question 12

What is the pipe-filter architectural pattern?

Answer 12

Processing of data is organized so each processing component is discrete and carries out one type of data transformation

Question 13

When should you use pipe-filter architectural pattern?

Answer 13

In data processing applications where inputs are processed at separate stages to generate related outputs

Question 14

What are the advantages and disadvantages of pipe-filter architectural pattern?

Answer 14

Advantages: workflow style matches the structure of business processes, evolution by adding transformations is straightforward
Disadvantages: format for data transfer needs to be agreed upon by communicating transformations

Question 15

What is coupling?

Answer 15

Measures system complexity by focusing on complexity between a module and other modules. Loosley coupled modules make it easy to connect to other modules with well-defined interfaces

Question 16

What is degree with respect to coupling?

Answer 16

The number of connections between the module and other which should be small for loose coupling

Question 17

What is ease with respect to coupling?

Answer 17

How obvious connections are between modules and others. Connections should be easy to make without needing to understand the implementation of other modules

Question 18

What is flexibility with respect to coupling?

Answer 18

Indicates how interchangeable other modules are for the module. They should be easily replaceable for something better in the future

Question 19

What are the signs that a system is tightly coupled?

Answer 19

Module connects to other modules through many interfaces
Corresponding modules to a single module are hard to find
Specific modules connected to a module cannot be interchanged

Question 20

What is cohesion?

Answer 20

Represents the clarity of responsibilities of a module to determine the complexity of the module

Question 21

How can you tell if a module has low cohesion?

Answer 21

Its purpose is not clear
It encapsulates more than one purpose
An encapsulation must be broken to understand a method

Question 22

What are the 5 SOLID design principles?

Answer 22

Single Responsibility Principle
Open-Closed Principle
Liskov Substitution Principle
Interface Segregation Principle
Dependency Inversion Principle

Question 23

What is the Single Responsibility SOLID design principle?

Answer 23

A class should do one thing and only have one reason to change

Question 24

What is the Open-Closed SOLID design principle?

Answer 24

Classes should be open for extension but closed to modification. We should be able to add new functionality without changing existing class code

Question 25

What is the Liskov Substitution SOLID design principle?

Answer 25

Subclasses should be substitutable for base classes as a child class extends behaviour but never narrows it down

Question 26

What is the Interface Segregation SOLID design principle?

Answer 26

Many client-specific interfaces are better than one general purpose interface as clients should not be forced to implement functions they don’t need

Question 27

What is the Dependency Inversion SOLID design princple?

Answer 27

High level modules for business logic should not depend on low level modules for utility features. Both modules should depend on an abstraction that couples the modules

Question 28

What are some important rules about naming variables, functions, and classes

Answer 28

1. Use nouns for objections, variables, classes, properties, and parameters
2. Use verbs for methods and functions
3. Use a standard naming convention like snake case or camel case
4. Use names the reveal the intention of the subject
5. Use pronounceable names for readability
6. Use searchable names
7. Avoid encodings
8. Don’t add unwarranted context

Question 29

What are some important rules about functions to keep code clean?

Answer 29

1. Functions should be able to fit on a single screen, no more than 10 lines
2. Functions should do one thing, do it well, and do it only
3. Allow one level of abstraction per function
4. Stay away from switch statements as they do more than one thing
5. Ideal number of arguments is 0, the less the better
6. Avoid changing parameters inside a function
7. A parameter should not be boolean

Question 30

What are some important rules about comments to keep code clean?

Answer 30

1. Keep comments updated with the code it references
2. Comments do not make up for bad code
3. Examples of good comments are legal comments, informative comments, those that explain intent, warn of consequences, are TODO comments, and amplify importance
4. Examples of bad comments are those that are redundant, create visual noise, are journal comments, and are commented out code

Question 31

Why is it preferred to throw an exception rather than return an error code

Answer 31

When you use an exception you know your code can handle faults, which faults it can handle

Question 32

What are the rules for nulls in clean coding?

Answer 32

Don’t return null from a function so your program doesn’t need to follow an alternate flow based on return value
Don’t pass nulls to functions so the function doesn’t have to handle alternate flows

Question 33

What order should the code in a class be organized in?

Answer 33

1. Public static constants
2. Private static variables
3. Private instance variables
4. Public functions
5. Private utilities called by a public function right after

Question 34

How can we measure class cohesion?

Answer 34

Classes should have a small number of instance variables and each method should manipulate one or more of the variables. The more variables it manipulates, the more cohesive it is to its class