CS257 Software Design
Wednesday, 16 April 2025

+ Demo: a tiny books web application & API

+ Web application structure
- Back end / server side
    - HTTP-based API implemented in Flask
    - Database managed by PostgreSQL
    - Web server for web pages
        using Flask and Jinja2 templates

- Front end / client side
    - HTML for content and structure
    - CSS for style
    - Javascript for interactivity

+ Our approach
- Bottom-up
- Back end first
- Why?
    - best way to help you learn one new technique at a time
    - sometimes it's a good plan anyway
    - can support separate teams working in parallel
    - downside: takes our focus off the user's needs for a while

+ Plan for the next 2.5 weeks: back end development

- Pick a question you want to ask of your data

- Build a command-line interface in python to answer that question
    - Design the CLI
    - Design a function to do the computation
    - Implement the function
    - Implement the CLI by taking advantage of the function

- Design a database to hold your data
    - Design the tables
    - Populate the tables

- Reimplement your function from the CLI above to access
    the database rather than the original data file

- Create an HTTP-based API endpoint for your question
    - Design the endpoint
    - Implement the endpoint in Flask

- Repeat all these steps as needed


+ Command-line interface (CLI) design & implementation
- What design principles have you seen in Unix commands?
- Quick look at built-in python CLI tools

+ Lab: implementing CLI in python