XML & URL Encoding

A URL, or Uniform Resource Locator, specifies the address of a resource on the Internet. Because URLs are limited to a subset of ASCII characters, it is sometimes necessary to replace "unsafe" characters with an encoded representation. In XML these encodings can be described using entities.

Entities in XML

Entities in XML begin with the ampersand (&) and pound sign (#) followed by the character encoding. The entity is terminated with a semicolon (;). For example, the encoding "&#37;" could be used to represent the percent sign. If the character encoding is preceded with an x, the encoding is assumed to be a hex encoding. For example, "&#x3C;" represents the less than (<) sign.

Predefined Entities

XML also defines several commonly used characters that are reserved in HTML and XML. For example, "&amp;" represents the ampersand character. The predefined entities in XML are amp, lt, gt, apos and quot.

Example

A URL to get an RSS feed might look like the following:

http://myurl.com/rss?get="myfeed('c:\feed.xml')"

Encoding this URL yields the following results:

http://myurl.com/rss?get=%22myfeed('c:%5Cfeed.xml')%22

The XML element for this encoding would be as follows:

<myURL>http://myurl.com/rss?get=%22myfeed(&apos;c:%5Cfeed.xml&apos;)%22</myURL>

References

• Blooberry.com: URL Encoding
• Network Working Group: Uniform Resource Locators (URL); T. Berners-Lee et al.; Dec 1994
• W3C: Extensible Markup Language (XML) 1.0; T. Bray et al.; Nov. 2008

Resources

• ASCIITable.com: ASCII Table and Description