UCLan¶

Software-Development¶

CO2401¶

Contents Page
Lecture PowerPoint
University/Year 2/CO2401 Software Development/Labs/Lab 3

Recap (Previous Lecture)¶

The previous lecture discussed CRC cards and class diagrams, as well as their different relationships.

_{Class Diagram Relationship Symbols}

Key Software Development Concepts¶

Abstraction: Using the right level of detail hiding irrelevant details

Modularity: Structuring a system into interacting components (modules) through decomposition of the system.

Coupling: Links between modules (Loose Coupling is good)

Cohesion: The simplicity of the purpose of module (High Cohesion is good)

Object Oriented Design¶

Break system into classes of objects with:
- Data (attributes)
- Functionality (methods) to manipulate the data

Helps provide a better match to reality than other development approaches.

Other objects interact (Collaborate) via:
- Calling each other's methods
- Must not directly change another objects data

Requirements are captured by a set of Use Cases
- Objects collaborate to deliver each Use Case.

Advantages of Object Orientation¶

Encourages good software engineering principles
- Abstraction:
- Modelling of only appropriate domain entities in the code
- Design Level (focus on 'what'.)

• Encapsulation
• Combining data and functionality in one entity
• Hiding of inner workings from other entities that don't need to see it

• Implementation Level (focus on flow)

• Loose Coupling

• Objects have minimum knowledge of each other

• Tight Cohesion

• A good object has a single purpose

Design: Working out how¶

UML diagrams become more detailed:
- Communication is aimed at developers not clients
- Detailed class diagrams
- Sequence diagrams
- Show objects' roles in implementing use cases

• State diagrams for complex software classes
• Package diagram showing organisation of software
• Deployment diagram: physical layout of software

Conceptualising the Domain¶

_{Diagram of conceptualising the domain}

Conceptual Class Model¶

What about the interface¶

Identifying Classes¶

Choosing suitable classes and attributes is crucial
- Avoid adding unnecessary complexity to the system

Creative Process
- There will be changes as you learn about the domain

Look for things in the text of the requirements:
- Objects represent "things" in the system domain so nouns and noun phrases can help identify possible classes
- The list of things give candidate classes for further analysis

Noun Phrase Example: Car Hire Company¶

CHC Example Information:¶

The CHC (Car Hire Company) stocks cars of a number of different models. It may have any number of cars of each model. The system should for each model hold the model's name and engine size. No two models have the same name.

A customer can borrow any car of a particular model that is not currently out on loan. However, no customer can have more than 3 cars on loan at once. A hired car must be returned within 14 days. When a customer returns a car it immediately becomes available on loan to other customers.

Each car has a unique Registration number.

Each customer of the hire company has a unique Customer ID, the system also holds each customer's name.

CHC Use Case Analysis (Methods)¶

Get Number Available: The staff member identifies the model of the car. The system displays the number of cars available.

List Models: The staff member identifies the customer. The system displays a list of models and return date(s) for the car(s) that the customer currently has out on loan.

Hire Car: The staff member identifies the car and the customer who is borrowing it. The system records the fact that it is no longer available for loan, due to the fact that the car is on loan to the member that was identified and the date it was hired.

Return Car: The staff member identifies the car. The system records the fact that this car is now available for loan and that it is no longer hired out to the customer who returned it.

Removing synonyms gives a list of Candidate Classes:
- Car Hire Company
- Car
- number of models
- number of cars
- model
- system
- model name
- customer
- loan
- day
- registration number
- customer number
- customer name
- staff member
- number of cars available
- list
- return date(s)
- fact
- date it was hired

Rejecting Candidate Classes¶

Is it simple property of some other candidate class?