A Uniform Resource Identifier (URI) is an object identifier in a web world. A URI can be any of the following: Uniform Resource Name (URN) , Uniform Resource Locator (URL), and Uniform Resource Characteristic (URC) . In this book, we will only discuss the URL.
Individual application protocols have their own URI scheme. A URI is specified by RFC 1738 as:
<scheme>:<scheme-specific-part>
where<scheme> can be, for instance, http (HTTP protocol), ftp (FTP protocol), mailto (SMTP protocol), nntp (NNTP protocol (news groups)), telnet (Telnet relation), file (local file), imap (IMAP protocol), ldap (LDAP protocol), or pop (POP3 protocol).
The schemes (but not in the whole URI) are not case sensitive, i.e., ftp is the same as FTP or Ftp.
Only ASCII characters occur in a URI. If you must use a non-ASCII character, it must be replaced with the % character followed by the hexadecimal code of the character. In the hexadecimal code of the character,...