Software Design

Software design can be worked out either from top down approach (customer/user requirements/features → code → data) or from bottom up approach (data → code → features).

Process

High Level Design

1. Define Requirements from user’s perspective
   1. product managers create PRD (Product Requirement Document) based on user feedback, data, market gaps
   2. Pick up the most important requirements
2. From the product requirements, extract features/abstract concepts and map them to data definitions, which then turn into objects in your database
3. define APIs through which data can be manipulated
   1. consider Network Protocols
4. Consider engineering requirements
   1. availability, reliability, extensibility, fault tolerance, etc
   2. Estimation of scale
5. Testing the design
   1. test flow through scenarios
   2. identify bottlenecks

Low Level Design

1. Consider
   1. memory optimizations
   2. User behaviour
   3. API calling
   4. Concurrency
   5. Latency
   6. Throughput
2. Perform Data modeling - use case diagram leading to class diagrams/ER diagrams
3. write pseudocode

Use Case Diagram

1. Define all the actors - users, stakeholders, operators, third party integrations, etc
2. Define requirements in terms of actions the actors can take
3. Convert the actions to objects → APIs and what services handle what
   1. The objects become the basis for class diagrams

Class Diagram

1. Every class needs
   1. States
      • data that an object needs to perform behaviours
   2. Behaviour