Characteristics of a URI
A Uniform Resource Locator (URL), is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifier (URI).
- URL's have different parts. Every URL MUST have:
- scheme, path and host
- URL's have different parts. Every URL MIGHT have:
- user information
Please click here for an example of these different parts. In your normal day-to-day use, you probably only use a scheme and a host.
A URL for HTTP (or HTTPS) is normally made up of three or four components:
- A scheme. The scheme identifies the protocol to be used to access the resource on the Internet. It can be HTTP (without SSL) or HTTPS (with SSL).
- A host. The host name identifies the host that holds the resource. For example, www.example.com. A server provides services in the name of the host, but hosts and servers do not have a one-to-one mapping. Refer to Host names. Host names can also be followed by a port number. Refer to Port numbers. Well-known port numbers for a service are normally omitted from the URL. Most servers use the well-known port numbers for HTTP and HTTPS , so most HTTP URLs omit the port number.
- A path. The path identifies the specific resource in the host that the web client wants to access. For example, /software/htp/cics/index.html.
- A query string. If a query string is used, it follows the path component, and provides a string of information that the resource can use for some purpose (for example, as parameters for a search or as data to be processed). The query string is usually a string of name and value pairs; for example, term=bluebird. Name and value pairs are separated from each other by an ampersand (&); for example, term=bluebird&source=browser-search.
The scheme and host components of a URL are not defined as case-sensitive, but the path and query string are case-sensitive. Typically, the whole URL is specified in lowercase.
The components of the URL are combined and delimited as follows:
- The scheme is followed by a colon and two forward slashes.
- If a port number is specified, that number follows the host name, separated by a colon.
- The path name begins with a single forward slash.
- If a query string is specified, it is preceded by a question mark.
Example of a URL
The following figure displays two example URIs and their component parts. 
hierarchical part ┌───────────────────┴─────────────────────┐ authority path ┌───────────────┴───────────────┐┌───┴────┐ abc://username:firstname.lastname@example.org:123/path/data?key=value&key2=value2#fragid1 └┬┘ └───────┬───────┘ └────┬────┘ └┬┘ └─────────┬─────────┘ └──┬──┘ scheme user information host port query fragment urn:example:mammal:monotreme:echidna └┬┘ └──────────────┬───────────────┘ scheme path
Purpose of a URL
A URL is a string of characters used to identify a resource. The purpose of a URL is to easily retrieve network resources. URL's also make linking to resources easier.
Do you understand this?
- identify each part of this URI:
- Which one of these does a URI NOT do:
- Enable easier access to resources
- Provide excellent resources for linking between resources
- Allow you to more quickly download content
- Provide a unified syntax to access remote resources
These standards are used from the IB Computer Science Subject Guide
- Identify the characteristics of a uniform resource identifier (URI) URL.
- Describe the purpose of a URL.
- IB Diploma Programme Computer science guide (first examinations 2014). Cardiff, Wales, United Kingdom: International Baccalaureate Organization. January 2012.