Uniform resource identifier (URI) and URL

Web Science

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).

• Please click here for the official url specification

• URL's have different parts. Every URL MUST have:
  • scheme and host
• URL's have different parts. Every URL MIGHT have:
  • user information
  • port
  • query
  • fragment

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.

Please click here to see a list of all the available schemes. There's a LOT more than HTTP and HTTPS!!

A URL for HTTP (or HTTPS) is normally made up of three or four components:

1. 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).
2. 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.
3. 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.
4. 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:

scheme://host:port/path?query

1. The scheme is followed by a colon and two forward slashes.
2. If a port number is specified, that number follows the host name, separated by a colon.
3. The path name begins with a single forward slash.
4. 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:password@example.com: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:

file:///Users/billdagjana/Desktop/

• 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

Standards

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.

a group or system of interconnected people or things.

A unit of abstract mathematical system subject to the laws of arithmetic.

Provide an answer from a number of possibilities. Recognize and state briefly a distinguishing fact or feature.

Provide an answer from a number of possibilities. Recognize and state briefly a distinguishing fact or feature.

Give a detailed account or picture of a situation, event, pattern or process.