URL strings consist of three parts (substrings):
1. network protocol
2. host name or address
3. file or resource location
protocol :// host / location
URL ProtocolThe 'protocol' substring defines a network protocol to be used to access a resource. These strings are short names followed by the three characters '://' (a simple naming convention to denote a protocol definition). Typical URL protocols include http://, ftp://, and mailto://.
URL HostThe 'host' substring identifies a computer or other network device. Hosts come from standard Internet databases such as DNS and can be names or IP addresses. For example, compnetworking.about.com is the host for this Web page.
URL LocationThe 'location' substring contains a path to one specific network resource on the host. Resources are normally located in a host directory or folder. For example, /od/internetaccessbestuses/bldef-url.htm is the location of this Web page including two subdirectories and the file name.
When the location element is omitted such as in http://compnetworking.about.com/, the URL conventionally points to the root directory of the host and often a home page (like 'index.htm').