The Ultimate Beginner’s Guide to URLs
The term URL is an acronym that stands for “Uniform Resource Locator.” The purpose of a URL is two-fold:
- to specify the address, or location, on the Internet of a particular document, file, page, or other resource.
- to specify the mechanism, or protocol, through which to retrieve that resource.
In keeping with its dual purpose, the URL consists of two parts, the resource name, which identifies the location of the resource, and the protocol identifier, or scheme name, which indicates how to retrieve it. The protocol identifier precedes the resource name in a web address and is immediately followed by a colon and a pair of forward slashes.
Examples of common protocol identifiers include: http://, https://, ftp://, telnet://, and gopher://.
Http stands for Hypertext Transfer Protocol, and is the most widely used protocol on the web today. Http is often used for payment transactions and other transactions that require encryption and high degree of security.
HTTP URLs: HTTP URLs are the most commonly used URLs on the Internet today. Because the HTTP protocols enabl the retrieval of inter-linked documents, files, and resources, it speeds up the development of the World Wide web. It is the HTTP protocol that allows users to move from one page on the web to another simply by clicking on a link in the first page retrieved. A typical HTTP URL is written in the following format: http://sitename.org/hypertext/protocol.
Ftp stands for File Transfer Protocol; this protocol is used to exchange and edit files between users over the Internet.
FTP URLs: With the widespread use of e-mail and the development of the World Wide Web, the FTP protocol is not used as commonly as it was during the 1990s, when the web was still in its infancy. However, FTP is still frequently used to upload and download files to and from Internet servers, often in the process of creating or revising a web site. An FTP URL is generally written in the following format: ftp://ftp.site.com/dir1/dir2/file.extension.
Telnet is a protocol used in communications between users over the Internet and enables interaction between a user’s computer and a remote computer or server.
Telnet URLs: The Telnet protocol enables the transfer of information via the Internet. It is important that the users be in communication to ensure that materials are transferred appropriately, there are limited permissions required for Telnet protocol.
Gopher is an Internet protocol first developed in the early 1990s which enabled users to search for and retrieve documents from the Internet. It was used widely in university settings but has now largely been overtaken by the web protocol Http. It remains an infrequently used but still extant alternative to the World Wide Web as a means of accessing and exchanging information over the Internet.
Gopher URLs: The Gopher protocol predates the rise of the World Wide Web. In the early days of the Internet, Gopher allowed users to search for, distribute, retrieve, and organize documents, files, and other resources online by accessing a remote host or server. Initially, the Gopher protocol could handle only text documents. It was supplanted in popularity and usefulness in the mid to late 1990s by the HTTP protocol which had the ability to handle graphics, html code, and hypertexts. Although a new version of Gopher that could handle hypertext documents was eventually developed, the protocol had already been eclipsed by HTTP. Only a few Gopher servers remain online, and most of the resources stored there have been converted to HTTP format or have been made accessible through the World Wide Web. Nonetheless, Gopher remains a little-used, but fondly remembered alternative to the web, and there have been recent calls for its revival. Gopher URLs are generally written in the following format: gopher://host:port/gopher-path.
The resource name specifies a host name, domain name, or an IP address for the server on which the Internet resource is to be found. In addition, a resource name may or may not include other elements, including the path through which the resource is to be retrieved, a port number, a query string, and an anchor. A URL is generally written in the following format or syntax: protocol identifier://host.name:port/path?query_string#anchor.
The portion of the URL that designates the host name or domain name is generally rendered in lower-case letters but is not case sensitive, and typing the name in capitals will retrieve the same web page. However, if information is included in the URL regarding the resource path, the path is generally case-sensitive, and using capitals when lower-case letters are required may result in an error message. The port number is generally optional, and, if no port number is typed into an Internet address box, most we browsers will simply connect to a default http port. A query string , if included in the URL, contains data that is transmitted to certain web applications during the resource retrieval process. Finally, the anchor, which is included in some URLs, specifies a particular location on a web page. The majority of URLs do not include query strings or anchors.
The following is an example of a URL. This URL specifies the location and retrieval protocol for the page on the White House web site that displays the biography of President Obama:
Example: http://www.whitehouse.gov/administration/president-obama.
http: indicates that the page is to be retrieved using the standard Hypertext Transfer Protocol. No port number is necessary or included because standard web browsers will default to the standard http port. “www.whitehouse.gov” specifies the domain name of the web site for the White House. The remainder of the URL, “administration/president-obama,” designates the path through which the page is retrieved. This URL does not include a query string or an anchor.
News URLs: A news URL is used to access a particular Usenet Newsgroup either directly from a news server’s drive or through a remote Network News Transfer Protocol (NNTP) server. NNTP is a special protocol used by news readers to retrieve Usenet news articles from news servers. Retrieval of documents over Usenet involves point-to-point transfers between a user’s computer and remote host computer using telephone connections. A news URL is written one of the following formats: 1) news:news.group or 2) news://domain.name.edu:port/news.group
File URLs: File URLs are generally used to retrieve files from a user’s own computer network or hard drive. Because it specifies location and retrieval method only for files on a particular host computer, a file URL is of limited utility in interactions between remote computers over the Internet. A file URL is written in the form: file://host/path.
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