Freebase

Freebase is a large collaborative knowledge base consisting of metadata composed mainly by its community members. It is an online collection of structured data harvested from many sources, including individual, user-submitted wiki contributions. Freebase aims to create a global resource which allows people (and machines) to access common information more effectively. It was developed by the American software company Metaweb and has been running publicly since March 2007. Metaweb was acquired by Google in a private sale announced July 16, 2010. Google's Knowledge Graph is powered in part by Freebase.

Freebase data is freely available for commercial and non-commercial use under a Creative Commons Attribution License, and an open API, RDF endpoint, and database dump are provided for programmers.

On 16 December 2014, the Knowledge Graph staff announced that it would be shutting down Freebase over the following six months. Google will provide assistance to Freebase users who want to make Freebase assertions suitable for inclusion in Wikidata.

Overview
On March 3, 2007, Metaweb publicly announced Freebase, described by the company as "an open shared database of the world's knowledge", and "a massive, collaboratively edited database of cross-linked data." Often understood as database model using Wikipedia-turned-database or entity-relationship model, Freebase provides an interface that allows non-programmers to fill in structured data, or metadata, of general information, and to categorize or connect data items in meaningful, semantic ways.

Described by Tim O'Reilly upon their launch, "Freebase is the bridge between the bottom up vision of Web 2.0 collective intelligence and the more structured world of the semantic web."

Freebase contains data harvested from sources such as Wikipedia, NNDB, FMD and MusicBrainz, as well as individually contributed data from its users. The structured data is licensed under the Creative Commons Attribution License, and a JSON-based HTTP API is provided to programmers for developing applications on any platform to utilize the Freebase data. The source code for the Metaweb application itself is proprietary.

Freebase runs on a database infrastructure created in-house by Metaweb that uses a graph model. This means that instead of using tables and keys to define data structures, Freebase defines its data structure as a set of nodes and a set of links that establish relationships between the nodes. Because its data structure is non-hierarchical, Freebase can model much more complex relationships between individual elements than a conventional database, and is open for users to enter new objects and relationships into the underlying graph. Queries to the database are made in Metaweb Query Language (MQL) and served by a triplestore called graphd.

Development
Danny Hillis first described his idea for creating a knowledge web he called Aristotle in a paper in 2000. But he said he did not try to build the system until he had recruited two technical experts as co-founders. Robert Cook, in parallel computing and database design, is Metaweb's executive vice president for product development. John Giannandrea, formerly chief technologist at Tellme Networks and chief technologist of the Web browser group at Netscape/AOL, is the company's chief technology officer.

Originally accessible by invitation only, Freebase opened full anonymous read access to the public in its alpha stage of development, and now requires registration only for data contributions.

On October 29, 2008, at the International Semantic Web Conference 2008, Freebase released its RDF service for generating RDF representations of Freebase topics, allowing Freebase to be used as linked data.