CLIENT-SERVER MODEL

Client-Server Model

An architecture where clients request services and servers provide responses.

Agenda of Client-Server Model

Discuss client-server architecture, scripting (client-side & server-side), communication between client & server, and one/two/three-tier models.

HTTP (Hypertext Transfer Protocol)

A stateless protocol for transferring information on intranets and the World Wide Web.

HTTPS

Secure version of HTTP, adds encryption for safe data transfer.

HTTP Request/Response

Standard communication between client and server where the client sends a request and server provides a response.

Client

An entity (browser, spider, or user agent) that makes an HTTP request to a server.

Server

Stores information, provides resources, and sends HTTP responses to clients.

Resources

Files or data provided by the server, accessed via URLs (Uniform Resource Locator).

Example of URL

http://www.tamk.fi/~jack/document.doc

HTTP Methods

Define actions on resources; most common is GET.

HTTP GET

Method where the client requests a representation of a resource from the server.

Steps of HTTP GET

1) Open connection 2) Send request (GET /path/file) 3) Read response.

Browser Role in GET

Creates HTTP request automatically when user opens a URL; includes info like user agent.

Example GET Request

GET / HTTP/1.1 Host: www.tamk.fi User-Agent: Mozilla/5.0

HTTP Response

Contains (1) header information and (2) resource itself.

Example Response

HTTP/1.1 200 OK + headers (date, server, content-length, content-type) + HTML resource.

HTTP Headers

Metadata in response (e.g., date, server type, content length, content type).

Client-Side Techniques

Executed on browser/plugins (e.g., Flash, JavaScript, Applets).

Server-Side Techniques

Executed on the server (e.g., PHP, Java EE) often using databases like MySQL.

Web Application Architecture

Works on client/server model where both client and server share processing responsibilities.

Client-Server Architecture

Network setup where many clients request/receive services from a server.

2-Tier Architecture

Client is the first tier, database server is the second tier.

3-Tier Architecture

Client is first tier, application server is second tier, database server is third tier.