PICS

PICS, the Platform for Internet Content Selection, is a system for associating metadata (PICS "labels") with Internet content. PICS provides a mechanism whereby independent groups can develop metadata vocabularies without naming conflict. The syntax of a PICS label is very compact and does not use any of the subsequent Web technology such as XML and XSL. RDF, the Resource Description Framework provides a model for representing metadata that is even more general than PICS, with more expressive power, and uses XML syntax. A goal of RDF was to permit the mechanical translation of PICS metadata into RDF form.

The first question to ask is: what is metadata? Metadata is "data about data", or specifically in our present context, "data about web resources."Metadata can be used in a variety of application areas; for example: in  resource discovery to provide better search engine capabilities, in  cataloging for describing the content available at a particular web site or page, by  intelligent software agents to facilitate knowledge sharing and exchange, in  digital signatures, in  content rating, and in many others (for example, metadata can be used for specialized tasks such as organizing a group of web pages for purposes of printing them as a single unit, or for producing a visualization of the link relationships between them).

At the core of the PICS infrastructure is the rating service. A  rating service is an individual, group, organization, or company that provides content labels for information on the Internet. The  rating service either chooses an existing, or develops a new  rating system to use in labeling content. The rating system specifies the range of statements that can be made. The rating service establishes criteria for determining who can label content using their name and how the labels must be applied. This combination of criteria and rating service are uniquely identified by the particular  service URL. This service URL becomes the brand, if you will, of the rating service. Policies determine what actions are taken based on the specific statements in the content label. If a content label is based on an unknown service URL, it is a simple (and potentially automatible) task to retrieve the appropriate service description file to understand what statements are being made in the label.