Faceted search, also called faceted navigation or faceted browsing, is a technique for accessing information organized according to a faceted classification system, allowing users to explore a collection of information by applying multiple filters. A faceted classification system classifies each information element along multiple explicit dimensions, enabling the classifications to be accessed and ordered in multiple ways rather than in a single, pre-determined, taxonomic order.
Facets correspond to properties of the information elements. They are often derived by analysis of the text of an item using entity extraction techniques or from pre-existing fields in a database such as author, descriptor, language, and format. Thus, existing web-pages, product descriptions or online collections of articles can be augmented with navigational facets.
The web search world, since its very beginning, has offered two paradigms:
Over the last few years, the direct search paradigm has gained dominance and the navigational approach became less and less popular. Recently, a new approach has emerged, combining both paradigms, namely the faceted search approach. Faceted search enables users to navigate a multi-dimensional information space by combining text search with a progressive narrowing of choices in each dimension. It has become the prevailing user interaction mechanism in e-commerce sites and is being extended to deal with semi-structured data, continuous dimensions, and folksonomies.
- Navigational search uses a hierarchy structure (taxonomy) to enable users to browse the information space by iteratively narrowing the scope of their quest in a predetermined order, as exemplified by Yahoo! Directory, DMOZ, etc.
- Direct search allows users to simply write their queries as a bag of words in a text box. This approach has been made enormously popular by Web search engines.
Within the academic community, faceted search has attracted interest primarily among library and information science researchers, and to some extent among computer science researchers specializing in information retrieval.
The most notable academic efforts in faceted search are the following:
- The CiteSeerX project at the Pennsylvania State University allows faceted search for academic documents and continues to expand into other facets such as table search.
- Apache Solr Search engine platform based on Apache Lucene.
Mass market use 
Faceted search has become a popular technique in commercial search applications, particularly for online retailers and libraries. An increasing number of enterprise search vendors provide software for implementing faceted search applications.
Online retail 
Online retail catalogs co-pioneered the earliest applications of faceted search, reflecting both the faceted nature of product data (most products have a type, brand, price, etc.) and the ready availability of the data in retailers' existing information-systems. In the early 2000s retailers started using faceted search, leading to its ubiquity as of 2012[update] in their online storefronts.
Although the noted librarian Ranganathan was a strong proponent of a faceted classification system for library materials, he did not succeed in replacing the pre-coordinated Dewey Decimal Classification system with his faceted colon classification scheme. Nonetheless, online library catalogs, also known as OPACs, have increasingly adopted faceted search interfaces. Noted examples include the North Carolina State University library catalog (part of the Triangle Research Libraries Network) and the OCLC Open WorldCat system.
See also 
- Exploratory search
- Faceted classification
- Human–computer information retrieval
- Information Extraction
- Enterprise Search
- Faceted Search, Morgan & Claypool, 2009
- Basics of Faceted Search
- SIGIR'2006 Workshop on Faceted Search - Call for Participation
- Internet Retailer: Most new e-commerce platforms designed with ‘faceted’ search, Venda says (2007)
- Major classification systems : the Dewey Centennial