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. The uniform resource locator - or URL - is the most important aspect of the internet. A URL defines a webpage: what a browser will display, how a browser may interact with a website, and in some instances how a browser treats and displays the returned results. Understanding the anatomy of a URL - what a URL is, what features a URL is comprised of, and how these features are used by a web browser and website - can help one better understand how to navigate the internet (and in some cases can help one navigate the internet more safely) as well as how one can create their own website URLs. A URL can be broken up into several features. While some of the features of a URL are optional, and in many cases not found within a typical URL, other elements are required to access a webpage or file on a website.: this element of a URL can take on many forms which represent the protocol for how data from a webpage will be transferred to a browser or client. Examples include http, https, and ftp.
Most ordinary websites use http or https, and any vital information should be transferred via https. Common transfer protocols include: http https ftp.: also known as website name or host name, the domain name element of a URL is often three parts: www (optional), second level name (eg algosome in www.algosome.com), and top level name(.com,.org,.edu,.net). The domain name is an instruction: telling your browser where to go to download the requested webpage. The 'www' portion is optional, and in many cases one can load a website with or without the www and receive the same content. This is not always the case however: in many cases using one may redirect a browser to the other format (eg algosome.com redirects to www.algosome.com). The top level domain often defines the type of website, some of the more regulated names include:.edu academic/educational site, typically a college or university.gov A website owned and operated by the government.org An organization.: The port is often omitted from a URL, and when omitted assumed to be port 80.
Anatomy Of A Url Pdf Format
When present the port occurs after the domain name, delimited from the domain name by a colon (for example, www.mydomain.com: 8080). A port is a communication point through which two computers communicate, the designation in the context of a URL defines which port to access on a website host.: the file name element of a URL is everything after the domain name, but before the file name ending (below). This is typically (though not always) just a path to a file located on the web server. File Format: often.html, but in many other cases can be.php,.cgi,.html. The file format often (but not always) depicts how the web server provides the content. For example, a.php ending is indicative that the webpage is being served by a php 'engine' - a scripting language which facilitates 'dynamic' webpages (pages which are physically one file but present different information depending upon given options).
Common formats include:.html.php.cgi.jpg/jpeg (pronounced 'jpeg') is an image file format, perhaps the most common on the internet today.: optional, the query string portion of a URL defines values sent to a website such that the website feeds the correct information. The query string is found after the first question mark in the URL, and is represented by key/value pairs separated by an ampersand (&). Query strings are used to send dynamic content - content which is created by the same file on the server but provides different content based upon parameters in the query string.: A fragment is defined as a number sign followed by a name. The fragment instructs a browser where to focus its attention, often by scrolling to the desired component. As an example, to the end of this URL and a browser will scroll down to this section.: although not physically part of a URL, browsers can send information to a web server - worth noting as they can be important players in internet navigation. These pieces of information include the browser name and version as well as 'cookies' - files downloaded previously from a website used to customize appearance (for instance, login information, shopping cart items, etc.).
The above features of a URL instruct a browser how to locate and download a file from a website. The domain name is first used to identify the web host. The file name and query string (if one exists) are then sent to the web host which uses this information to locate the appropriate file. Often the web host uses scripts - files which send different information based upon the requested content. Lastly, the website sends the content - be it a webpage, file, or image - back to the web browser, which in turn displays the content of the webpage.
URLs (Uniform Resource Locators) are the standardized means o f addressing pages in the Web. Technically, a URL (presumably pronounced like the name of the psychic known for bending spoons) is any short string leading to a resource that is acceptable for use on the Web, while it also identifies a specific protocol for retrieving the resource.
Though this meaning is slightly different in case URI, URN, URP, URT & URVs. In the above acronyms, the 'U' is sometimes construed as standing for 'Universal' rather than 'Uniform'. URLs have the following form.
The first part, separated by a colon (:) from the rest of the URL, is the protocol, u sually http for HyperText Transport Protocol, though other protocols such as ftp and gopher are sometimes used. For secure-server sites using an encrypted protocol, https is used as the protocol identifier. Next comes the hostname (domain n ame or IP address), preceded by a double slash (//).
It seems to be a common misconception that the colon and double slash are an inseparable delimiter terminating the protocol - for instance, the Mozilla team posted an online document regarding their implementation of irc:// URLs. Actually, the colon is the terminator of the protocol section, and the double slash is used to introduce a hostname or other site identifier (varying somewhat by protocol, with some less-common protocols taking things other than domain names in this section) and is absent in URIs lacking a hostname like mailto: and news: URLs. After that is the directory path to the Web page you're accessing, with forward slashes (/) separating directory levels (not backslashes ( ) like in DOS/Windows systems). There are a few special protocols with URLs of differing syntax. Mailto: is followed with an e-mail address to create a link allowing users to send mail to that ad dress.
News: is followed by the name of a newsgroup (e.g., comp.infosystems.www.authoring.html) to let the user follow the link to see the newsgroup's messages (if the user's browser is configured to access a news server). Both of these URL types do not have slashes (single or double) in them; the syntax looks like mailto:webmaster@webtips.dan.info, not. Mailto://webmaster@webtips.dan.info/; developers used to the more common http: syntax often put extra slashes in these URLs and cause them to fail. (More information on mailto: URLs is in my page on e-mail.) Note that you can't leave out the protocol and use www.somewhere.com as a link URL without the This syntax works when you're typing in a URL in most browsers, but in a link within your Web site it will be interpreted as a relative URL to a file named 'www.somewhere.com' in the current directory. Are URLs case sensitive? Technically, yes.
You should always be consistent in your use of upper or lower case in your URLs. Even in cases where the upper and lower case versions go to the same resource, you're imposing an unnecessary burden on browsers that need to retrieve and cache two copies of the same thing if they go to two variants of the same URL. As far as whether you can vary the case and still get the same resource, this depends. The protocol and hostname are not case sensitive, so you can write or HTTP://www.dan.info/ and they'll work identically. However, the directory and filenames may be case sensitive depending on what operating system the server is running under (UNIX is case-sensitive, while Windows isn't). Fragment names are case- sensitive.
So be careful to match the directory, file, and anchor names in your links to the case of the actual files and anchors. Can I include spaces in my URLs?
No, the space is not a legal character in URLs. Spaces, and a number of other special characters, must be encoded by using a percent sign (%) followed by a two character hexadecimal number giving the character's position in the ASCII or ISO LATIN-1 encoding. A space is represented as%20. Some Web servers might have file systems that allow documents with names containing spaces, but if you use files with such names, their URLs will contain%20, which is rather ugly. So it's best to avoid such names and stick to safer characters like letters, numbers, dashes, and underscores. Mac users in particular tend to create directory structures including spaces, producing awkward URLs.
Relative URLs Definition: Relative URLs are context-sensitive, giving a path with respect to your current location. There are several types of relative URL. A URL with no slashes, like 'junk.html', references another page in the same directory as the current page. So if you're cu rrently at 'uff/one.html' and encounter the relative URL 'two.html', this is addressing the page '.
A URL with no leading slashes, but slashes within, references a subdirectory beneath the current one. 'subdir/test.html', encountered from the same page as the above example, would reference '/test.html'. A URL with double dots at the start, like './another.html', references the parent directory of the current one. This URL, accessed from the same page as the above examples, would lead to 'another.html'. Double dots can be repeated, like '././grandparent.html', to go up additional levels, or combined with subdirectory references like './sister/' to go to a sibling directory. A URL with a single dot at the start, like './stuff.html', references another file in the same directory, just like a URL with no slashes.
It's better to use the form of URL without the dot and slash, since there are a few old browsers and indexing robots that don't seem to understand this syntax properly, and end up expanding the URLs into bizarre things like ' e.com/././stuff/./junk/', which work (with most servers), but look weird in your access logs. Double dots produce this effect too, but they're too useful to give up, but the single dot is unnecessary (except in the special case of linking back to the index of the current directory, where './' is the best URL, as described elsewhere).
A URL with a slash at the start, like '/dir1/dir2/stuff.html', references a page at a path starting from the root of the server. To be more precise, it starts at the root of the domain name you're in. Be careful using this if your site is in a virtual domain on an Internet provider's system. If you have a domain yoursite.com which points at the directory /sites/yours/ within the ISP's domain provider.com, then your page silly/stuff.ht ml can be reached via two different URLs: lly/stuff.html an d ours/silly/stuff.html. Maybe you had your site up for a long time before getting your own d omain so your users are regularly coming in via both addresses.
Anatomy Of A Url Address
In this case, a URL like '/silly/mores tuff.html' can be interpreted as 'lly/morestuff.html' or 'morestuff.html' depending on which domain the user is in. Thus, you should avoid this form of URL if there's any doubt about h ow the user is accessing your site. In an uncommon b ut legal URL form, a URL with a double slash at the start, like '//www.yoursite.com/stuff.html', keeps only the protocol identifier from the current URL and gets the full sitename and path from the new URL. I actually found a use for this form recently, in a piece of HTML code that was being accessed under both the secure https: protocol and the nonsecure http: protocol, and under more than one domain name. I wanted to access a particular graphic in all cases, using a protocol (secure or nonsecure) matching that with which the main page was accessed.
Using relative URLs of the forms given above would require the graphic to be placed in all the different domains; and using an absolute URL would force the protocol to be specified. I d eftly avoided these problems by using a double-slashed relative URL. Finally, a URL beginning with a pound sign (#) specifies a link to a fragment identifier (anchor) in the current page.
Which Type of URL Should You Use?