P3P

P3P, Platform for Privacy Preferences,  is a protocol designed to allow Web sites to present their data-collection practices in a standardized, machine-readable, easy-to-locate manner. Second, it enables Web users to understand what data will be collected by sites they visit, how that data will be used, and what data/uses they may "opt-out" of or "opt-in" to.

P3P encodes data-use practices in a machine-readable XML format known as a  P3P policy. The P3P specification defines:

• A standard schema for data a Web site may wish to collect, known as the "P3P base data schema"
• A standard set of uses, recipients, data categories, and other privacy disclosures
• An XML format for expressing a privacy policy
• A means of associating privacy policies with Web pages or sites
• A mechanism for transporting P3P policies over HTTP

P3P is an XML/RDF syntax for the automated exchanges between user agents (Web browsers, proxy servers) and services.  Most often a service is a Web site, but it may be applications that collect user information.

P3P defines 10 distinct categories of data that may be considered to be private.  These include physical contact information, online contact information, unique identifiers, financial account numbers, computer information navigation and click-stream data, interactive data, demographic data, preference data, and content.

P3P is the work of the W3C Society and Technology domain.