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STUDY GUIDE · GKU 9

Web and mobile systems: how they work and how to build them safely study guide (Information Technology)

Most systems an IT graduate supports are reached through a browser or a phone. This unit follows a request from the user's screen to the database and back. It covers the client–server model and HTTP (methods, status codes, caching), REST APIs and JSON; the front end built from HTML, CSS and responsive layout; mobile platforms and the choice between native, cross-platform, hybrid and progressive web apps; validating data on the client for speed and on the server for safety; what runs on the client and what must run on the server, with scripting for the web, the server and the operating system; cookies and sessions with their security attributes; connecting server code to a database with parameterised queries and transactions; and JavaScript itself, from types and scope to the DOM and asynchronous requests. Security appears where it belongs, as the defensive version of each technique.

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Structured by the official ETEC subject standard for this topic: every listed topic and learning outcome, with formulas, figures and worked examples. The full sections are available to members in the app.

SKU 9.1 · Web and mobile systems concepts and technologies

  1. How the web works: clients, servers, HTTP and APIs

    The parts of a web system (browser, web server, application server, database, analytics) and the path of one request; URLs; HTTP requests and responses, methods and status codes; caching with Cache-Control and ETags; REST APIs that exchange JSON; and the frameworks industry builds these with.

  2. The front end: HTML, CSS and responsive layout

    What HTML, CSS and JavaScript each do in a page; semantic HTML and forms; how CSS decides which rule wins (specificity and source order) and how much space a box takes (the box model); and responsive design with the viewport, relative units, a fluid grid and mobile-first media queries.

  3. Mobile platforms and app types

    Android and iOS and how apps reach them; native, cross-platform, hybrid and progressive web apps compared; and the constraints that shape every mobile design: small touch screens, unreliable networks, battery, permissions, the app life cycle and old versions still in use.

  4. Data validation on the client and on the server

    What to check about an input (presence, type, format, range, length, consistency, meaning, uniqueness), why the client checks for speed and the server checks for safety, allow-lists and real-value checks, and why validation is a different defence from output encoding and parameterised queries.

  5. Client-side and server-side development, and scripting

    What runs in the browser or app and what runs on the server, and why the line between them is a trust boundary; server-side, client-side and static rendering; and scripting languages in their three roles: web scripting in the page, server-side scripting behind it, and operating-system scripting that automates the machines.

  6. Cookies and sessions

    How a server makes a stateless protocol remember a user: Set-Cookie and Cookie headers, the attributes that decide where and how long a cookie is sent (Domain, Path, Expires and Max-Age, Secure, HttpOnly, SameSite), replacing and deleting cookies, reading them from JavaScript, server-side sessions, and the attacks each attribute defends against.

  7. Server-side database connectivity

    How server code reads and changes a database: drivers, connection settings kept out of the code, connection pools, executing statements and fetching rows, mapping API requests to SQL, parameterised queries against SQL injection, transactions that keep related changes atomic, and turning database errors into proper responses.

  8. JavaScript: the language of the web page

    The parts of JavaScript an IT specialist must read and write: let, const and var with their scope and hoisting; types, typeof and the coercion traps; selection and repetition; functions, parameters, defaults and closures; arrays, objects and JSON; the DOM and events; and fetch with async and await.

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