Others have called for similar services. These include organizations that want to rate content based on information quality, vendors of filtering software who wish to make their products interoperable with other PICS-compatible products and labels, and content providers and resource discovery companies developing advanced search tools, and even some libraries wanting to restrict access to inappropriate content. Filtering is the process whereby software can select the relevance or appropriateness of content delivered to a user, based on either criteria established by a third party or by the user. Filters make content inaccessible to some users. The software filters use labels or ratings attached to the content to indicate to the software whether or not it should be presented to the user.
Labels are descriptions of the content.
The determination about how labels or ratings are applied to content is based upon ratings vocabularies that have been established through a variety of third-party sources. Because these vocabularies are written in a PICS format, they can be shared with distribution and filtering software and services. Rating vocabularies are the subject of considerable public scrutiny and debate. Content filtering can be effected by the client software, the content server, or through a third-party service. All filtering services necessarily introduce delays in serving results as an additional level of processing of requests is required.