Web application Basics

🔷 What is a Web Application?

A web application is a software program that runs on a web server and is accessed by users through a web browser using the internet or an intranet.

Unlike traditional desktop applications, web applications do not need to be installed on a user’s machine.

🔷 Components of a Web Application

Client (Front-End)
Runs in the user's browser
Built using HTML, CSS, JavaScript
Handles user input, interactions, and display
Server (Back-End)
Processes business logic
Communicates with the database
Returns data or web pages to the client
Database
Stores user data, content, and application state
Commonly used databases: SQL Server, MySQL, Oracle, MongoDB

🔷 Types of Web Applications

Type	Description
Static Web App	Delivers fixed content (e.g., HTML pages)
Dynamic Web App	Generates content dynamically (e.g., ASP.NET)
Single Page Application (SPA)	Loads a single HTML page and updates dynamically (e.g., React, Angular)
Progressive Web App (PWA)	Works like a native app, supports offline use

🔷 Web Application vs Desktop Application

Feature	Web Application	Desktop Application
Installation	Not required	Required
Accessibility	Accessible via browser	Runs on specific machine
Update & Maintenance	Easier (centralized server)	Harder (needs manual update)
Performance	Depends on internet & server	High performance on local machine

🔷 ASP.NET for Web Development

ASP.NET is a framework developed by Microsoft for building dynamic web applications using .NET languages like VB.NET or C#.

Features:

Server-side processing
Web Forms and MVC support
Session and state management
Security features like authentication and authorization
Rich set of controls and libraries

🔷 Life Cycle of a Web Application Request

Request: Browser sends an HTTP request to the server.
Routing: Server routes the request to the correct handler (e.g., a .aspx file or controller).
Processing: Code runs on the server; data is fetched from DB if needed.
Response: Server returns an HTML response to the browser.
Rendering: Browser displays the result to the user.

🔷 Tools Used for Web Development

Visual Studio: For ASP.NET development
IIS (Internet Information Services): Web server for running ASP.NET apps
Web Browsers: Chrome, Firefox, Edge for testing UI
SQL Server: Database backend

🔷 Advantages of Web Applications

Platform independent (runs in any browser)
Centralized updates and deployment
Easy access from anywhere
Scalable and maintainable
Cross-device compatibility

🔷 Real-Life Examples

Gmail
Online banking portals
E-commerce websites like Amazon
Online reservation systems
College/student portals

📌 Summary:

A web application runs on a server and is accessed via a web browser.
It has three main parts: Client, Server, and Database.
ASP.NET is widely used to develop .NET-based web apps.
Web apps are easier to maintain and update compared to desktop apps.

Web Application Fundamentals

🔷 What Are Web Application Fundamentals?

Web application fundamentals refer to the core concepts, architecture, and technologies that are essential for building and running web-based applications. Understanding these basics is crucial for developing reliable, scalable, and user-friendly web apps.

🔶 1. Web Application Architecture

A typical web application is based on the Client-Server Model, consisting of:

Component	Role
Client (Frontend)	User interface part (runs in the web browser)
Server (Backend)	Handles business logic and processes client requests
Database	Stores data (like users, orders, etc.)

🔶 2. HTTP Protocol

Web apps communicate using HTTP (HyperText Transfer Protocol) or HTTPS (secure).
It is a stateless protocol, meaning each request is independent and doesn’t remember previous interactions.

Common HTTP Methods:

Method	Purpose
`GET`	Retrieve data
`POST`	Submit data
`PUT`	Update existing data
`DELETE`	Remove data

🔶 3. URL and Routing

Each web page or functionality has a unique URL (Uniform Resource Locator).
Routing maps a URL to specific code (e.g., a page or a controller method in ASP.NET).

Example: https://myapp.com/products → Products.aspx or ProductsController.cs

🔶 4. Frontend Technologies

The frontend is what the user sees and interacts with. It includes:

Technology	Purpose
HTML	Structure of the page
CSS	Styling and layout
JavaScript	Interactivity and client-side logic

Modern frameworks: React, Angular, Vue

🔶 5. Backend Technologies

Backend processes requests, performs logic, and communicates with databases.

In .NET, backend can be built using:
ASP.NET Web Forms
ASP.NET MVC
ASP.NET Core

It handles:

Authentication
Business logic
Database communication
Session management

🔶 6. Databases

Web apps often need to store and retrieve data. Common databases:

Type	Example
Relational	SQL Server, MySQL
NoSQL	MongoDB

In .NET apps, ADO.NET or Entity Framework is used to interact with databases.

🔶 7. State Management

Since HTTP is stateless, web apps use state management to remember user information across pages.

Technique	Description
Session State	Stores data for one user session
Cookies	Small pieces of data stored in the browser
ViewState	Stores control values between postbacks (Web Forms)
Query Strings	Passes data via URL parameters

🔶 8. Security Fundamentals

Web apps must handle security properly. Common measures:

Security Feature	Purpose
Authentication	Verifies user identity (login system)
Authorization	Controls what the user can access
Input Validation	Prevents SQL injection, XSS, etc.
HTTPS	Encrypts communication

🔶 9. Development Environment

Visual Studio: IDE for developing ASP.NET applications
IIS (Internet Information Services): Web server for running .NET web apps
.NET Framework / .NET Core: Runtime for executing .NET applications

🔶 10. Deployment

Web applications are deployed to a web server (like IIS or Azure App Service). Users access it via a browser from anywhere.

📌 Summary Table

Concept	Description
Web app architecture	Client-server + database
HTTP	Stateless communication protocol
Frontend	HTML, CSS, JavaScript
Backend	ASP.NET handles logic
Routing	Maps URLs to code
Database	Stores persistent data
State management	Maintains user data across pages
Security	Protects against threats
Tools	Visual Studio, IIS
Deployment	Hosting the web app

ASP.NET Application Fundamentals

🔷 What is ASP.NET?

ASP.NET is a web application framework developed by Microsoft that allows developers to build dynamic websites, web applications, and web services using .NET languages like VB.NET or C#.

It runs on the .NET Framework (or .NET Core/.NET 5+ in newer versions) and uses the HTTP protocol to communicate between browser (client) and web server.

🔷 ASP.NET Application Structure

An ASP.NET web application typically includes:

Component	Description
`.aspx` pages	Web Forms with HTML UI and server-side logic
`.aspx.cs` or `.vb`	Code-behind files (written in C# or VB.NET)
`web.config`	Configuration settings (e.g., security, session, database)
`Global.asax`	Global application events like start, end, error
`App_Code` folder	Shared classes and utility functions
`App_Data` folder	Databases or data files used by the application

🔷 ASP.NET Page Life Cycle

Each time a user requests a page, the ASP.NET engine follows a life cycle:

Stage	Description
Page Request	Client requests a .aspx page
Start	Sets properties like `IsPostBack`
Initialization	Controls are initialized (ID set)
Load	Loads control properties and view state
PostBack Events	Executes user events like button clicks
Rendering	Page is converted to HTML
Unload	Final cleanup and memory release

🔷 Server-Side vs Client-Side

Server-Side (ASP.NET)	Client-Side (Browser)
Code executes on server	Code executes on user’s browser
Uses C# / VB.NET	Uses JavaScript / HTML / CSS
Secure and hidden	Visible and editable in browser
Can connect to database	Cannot directly connect to database

🔷 Web Forms in ASP.NET

Built using .aspx pages and controls
Drag-and-drop controls from the toolbox (e.g., Button, Label, GridView)
Use runat="server" to make controls accessible in code-behind
Event-driven (e.g., Button_Click)

Example:

<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />

Code-behind:

protected void btnSubmit_Click(object sender, EventArgs e)
{
    lblMessage.Text = "Submitted!";
}

🔷 Key ASP.NET Features

Feature	Description
State Management	Maintains user data using Session, ViewState, Cookies
Validation Controls	Validates input (e.g., RequiredFieldValidator)
Master Pages	Provides consistent layout for multiple pages
Themes and Skins	Provides styling for controls and pages
Data Binding	Connects controls like GridView to databases
Security	Login controls, roles, membership providers

🔷 Configuration with web.config

Central XML file to store settings

Examples:

Database connection strings
Authentication rules
Custom error pages
Session settings

<connectionStrings>
  <add name="MyDB" connectionString="Data Source=..."/>
</connectionStrings>

🔷 ASP.NET Compilation Model

Pages are compiled into assemblies (DLLs) the first time they are accessed.
Faster execution after first request.

🔷 Deployment Options

IIS (Internet Information Services): Microsoft’s web server for hosting ASP.NET apps
Azure Web Apps: Cloud deployment for ASP.NET
FTP / Web Deploy: Traditional file transfer

📌 Summary Table

Feature	Description
ASP.NET	Framework for building web apps using .NET
Page Life Cycle	Series of events from request to response
Web Forms	Visual, event-driven pages using controls
web.config	Stores app settings
State Management	Session, ViewState, Cookies
Deployment	Via IIS, Azure, or other hosts