学习Databases and Interfaces 的课堂笔记

Introduction

Outline

• The Internet
• Transmission Control Protocol / Internet
• Domain name
• Uniform (or Universal) Resource Locator (URL)
• Hyper Text Transfer Protocol

TCP/IP

• Transmission Control Protocol / Internet Protocol (TCP/IP) allows devices on the internet to communicate with each other.
• IP addresses are used to uniquely identify all devices connected to the internet

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Domain Name

• Beigins with the name of the host machine, followed by progressively larger collections of machines i.e.domains.
• Easier to remember than IP addresses (for humans).

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World Wide Wed

• A vast collection of documents that are connected by links.

Hypertext Transfer Protocol

• HTTP consists of :request or response.
  • Users issues URL from a browser http://host:port/path.file
  • Browser sends a request message.
  • Server maps the URL to a file or program under the document directory
  • Server returns a response message
  • Browser formats the response and displays

Uniform Resource Locators

• URLs are a path to, or locations of, a resource on the Internet.
• URL format is : scheme : object- address
• The scheme is often a communication protocol, e.g. HTTP,FTP

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Passing Parameters using URL

-URL parameters are probably the easiest way of passing variables from one webpage to another.
-GET method is used to request data from a specified resource.
-POST method is used to send data to a server to create or update a resource.

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URL and Partial Path

• The path to the dicument for the HTTP protocol is similar to a path to a file or directory in the file system of an operating system.
• BUT, the URL may not include all directories i.e. partical path

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• The actual location of a file in the file system of a web server can be different from the URL e.g
  a file in. ./var/site/forum/index.phpmaybe access usinghttp://www.site.ru/forum/index.php
• In PHP, the file can be accessed using
  $path = $_SERVER['DOCUMENT_ROOT']."/forum/index.php"

Using index.html as a Security Feature

• Sometimes a user may specify a directory but a document name is not given.
  http://www.yourwebsite.com/yourfolder
• The web server will search for a servable document e.g. index.html
• If a servable document is not found, by default, a directory listing will be returned i.e. all files in that directory. => 404

Conclusions

• Devices connected on the Internet rely on TCP/IP protocol to communicate.
• IPv4 addresses are four-part numbers xxx.xxx.xxx.xxx
• DNS translates IP addresses to domain names so as to be human readable
• URN/URI identify resources on the Internet, URL identify paths or locations of the resources.
• HTTP is a standard protocol for web communicaiton.
• Commonly used HTTP requests are GET and POST.