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URL - (Uniform Resource Locator) is the address that defines the route to a file on the Internet.
URI (Uniform Resource Identifier) - A more general term. A URI can be classified as a locator, a name, or both. The term "Uniform Resource Locator" (URL) refers to the subset of URI that identify resources via a representation of their primary access mechanism (e.g., their network "location"). It is now also used to define a scheme which is the first part of a URL. (See: RFC 2396)
See URIs, URLs, and URNs: Clarifications and Recommendations at W3.org
Most web addresses (URLs) are of the form http://www.w3.org/Protocols/Specs.html
user:password@ is an otpional login used for a few services like telnet.
The domain is defining the Internet domain name like w3.org.
The host is defining the domain host. If omitted, the default host for http is www.
The :port is defining the port number at the host. The port number is normally omitted. The default port number for http is 80.
The path is defining a path (a sub directory) at the server. If the path is omitted, the resource (the document) must be located at the root directory of the Web site.
The filename is defining the name of a document or program. The default filename might be default.asp, or index.html or something else depending on the settings of the Web server. See file type below.Http is the most common scheme used on the web, but Browsers can also access servers using other (schemes). Following are some examples of the most common types. Some such as ftp, file and mailto work automatically and others require some configuration.
Note: Common types http, https, ftp, file are built into browsers.
ftp, file and gopher are basically file transfer schemes which will download files from a server. http also transfers files, but does much more; It will allow you to specify a program to run after the file is downloaded, e.g. MS word for a .doc file or display some files itself e.g. .gif images. (See file type below.) It also has the ability to send user information input in a form back to a server.
Other schemes usually require a separate program, which can be configured in your browser, to handle the communication to the server. Mailto, and news are built into Netscape, but will default to Outlook Express with Internet Explorer (IE).
You don't always see the scheme when you click on a link in the internet. For example the link on the internet for a Real Audio streaming audio may be something linke http://whyy.org/91FM/live40.ram. This will download a file which contains "rtsp://streamer.whyy.org/encoder/live.rm" the rtsp scheme is used by the real audio player. See other multimedia schemes below.
Scheme Description and Example ______________________________________ http: Hypertext Transfer Protocol - File on a World Wide Web server. e.g. http://www.w3.org/Protocols/ https: Hypertext Transfer Protocol Secure - http over SSL (Secure Socket Layer) for encryption. ftp: File on a File Transfer Protocol Server. e.g. ftp://ftp.research.telcordia.com/ file: This is similar to ftp but usually denotes file on a local host that is not necessairly available over the internet. e.g. file:///C:\My Documents/ on Windows 98 mailto: Send mail. (Note: you may need to specify a mail program in your browser) e.g. () news: Read news on a Usenet newsgroup. e.g. news:comp.infosystems.www.browsers.misc (Note: You may need to specify a netnews reader program in your browser.) Others: telnet: Open an interactive terminal window with a telnet server. Most of the following require configuration to specify an external application. imap: Internet Message Access Protocol (mail access) ldap: Lightweight Directory Access Protocol nntp: USENET news using NNTP (Net News Trsnsport Protocol) access pop: Post Office Protocol v3 (mail access) rtsp: Real Time Streaming Protocol Replaces proprietary Progressive Networks Media (PNM) protocol im: Instant Messaging - part of Instant Messaging and Presence Protocol (IMPP) pres: Presence - part of Instant Messaging and Presence Protocol (IMPP) sip: session initiation protocol - For instant messaging and netphone (VoIP). h323: ITU-T Standard H.323 - multimedia communications services over packet based networks RFC3508 used for NetMeeting, CUworld or Intel NetPhone daap: Digital Audio Access Protocol (Apple) itms: iTunes Music Store (Apple Music downloads) netphone: Voice over IP (VoIP) phone calls tel: Telephone e.g. tel:1-212-555-1212 fax: FAX modem: Modem Older schemes not popular now: gopher: A gopher server. (Similar to ftp but with file descriptions) wais: A wide area information server. e.g. WAIS directory-of-servers indexFile Type
In addition to the scheme which tells the browser how to access the file, the File Type determined by the "File Name Extension" will determine how to display it when it arrives. The browser can display some files directly (e.g. .html, .txt, .gif, .jpg) while others require plug-ins (e.g. .pdf) or links to other programs (e.g. .doc [MS Word], .xls [MS Excel]) or Windows Media Player (WMP) for audio/video or the RealOne Player for streaming audio.
Schemes and Protocols:
file scheme Program .ram rtsp:...file.rm Real Time Streaming Protocol Real Audio .asfSee Also:
RFC 1738 - URL
URI Schemes at W3.org and IANA
File Name Extension
Protocols and Ports
Internet Scheme Syntax