Software Engineering For Beginners
What is Software Design ?
- It is a Process of planning system architecture and components.
Important Concepts
Abstraction : hiding unnecessary details.
Modularity : dividing system into smaller modules.
Cohesion : how closely related functions are inside a module. & high cohesion is good.
Coupling : dependency between modules. & low coupling is good.
Abstraction
Abstraction is the process of hiding unnecessary implementation details and exposing only the essential features of a system or component.
Simple example : driving a car : you know how to drive without knowing how the engine works internally , in programming: a function hides the internal logic, and you just call it.
Importance : reduces complexity , makes software easier to understand , helps in reusability and maintenance
Modularity
Modularity is the design principle of dividing a system into smaller, independent modules that can be developed, tested, and maintained separately.
Simple example : a banking system
- Module 1 : accounts
- Module 2 : transactions
- Module 3 : loan processing
Each module can work independently.
Importance : simplifies development , easier testing and debugging , encourages reuse of modules
Cohesion
Cohesion measures how closely the functions inside a module are related to each other.
- High cohesion : all functions in a module serve a single, well-defined purpose : good design.
- Low cohesion : module has unrelated functions : poor design.
Simple example:
- High cohesion: a “login module” only handles authentication
- Low cohesion: a “login module” also manages user payments and reports : bad design
Importance: easier maintenance , better readability , modules can be reused
Coupling
Coupling measures how dependent one module is on another module.
- Low coupling : modules are independent : good design
- High coupling : modules depend heavily on each other : bad design.
Simple example:
- Low coupling: “payment module” only communicates via an interface with “accounts module”
- High coupling: “payment module” directly accesses all functions of “accounts module” : changes in one affect the other
Importance:
- Low coupling : easier maintenance and testing
- High coupling : changes in one module ripple through system
Uml ( unified modeling language )
- Uml is a standard visual modeling language used to design, visualize, and document software systems.
- Helps represent system structure and behavior before actual coding.
- Widely used in object-oriented software engineering.
Use case diagram
A use case diagram shows how users (actors) interact with the system.
Key elements:
- Actor: external entity interacting with the system (user, external system)
- Use case: functionality or service provided by the system
Example:
- Actor: customer
- Use cases: login, make payment, generate report
Class diagram
A class diagram shows the static structure of a system by representing classes, attributes, methods, and relationships.
Key elements
- Class: rectangle divided into 3 parts (name | attributes | methods)
- Relationships: inheritance, association, aggregation, composition
Example
- Class: bank account
- Attributes: account number, balance
- Methods: deposit(), withdraw()
Sequence diagram
A sequence diagram shows the flow of interaction between objects over time.
Key elements
- Objects/participants: represented as rectangles
- Messages: arrows showing communication
- Lifelines: dashed vertical lines representing object lifetime
Example
- Customer : atm : bank server
- Messages: insert card(), validate(), dispense cash()
Activity diagram
An activity diagram models the workflow or sequence of activities in a system or process.
Key elements:
- Activity: action or operation
- Decision: conditional branching
- Start/end nodes: indicate start and finish of workflow
Example :
- Online shopping workflow:
- Start : login : select product : add to cart : payment : end
