GoodRelations is a lightweight ontology for exchanging e-commerce information, namely data about products, offers, points of sale, prices, terms and conditions, on the Web. It can be used in all RDF syntaxes (like RDF/XML, Turtle, RDFa, JSON-LD, ...), Microdata, and basically any syntax that supports an Entitity-Attribute-Value pattern.

GoodRelations started as an independent Web Ontology in 2007, see here for more information on the history. Since November 2012, it has been almost fully integrated into schema.org and is now the official e-commerce data model of this initiative.

GoodRelations stays an independent project and will remain the official version of the conceptual model. While a majority of GoodRelations data published on the Web will be in the schema.org namespace, the original version will be the default way of handling respective data in a full RDF/SPARQL/OWL environment.

GoodRelations provides a standard vocabulary for expressing things like

that a particular Web site describes an offer to sell cellphones of a certain make and model at a certain price,
that a pianohouse offers maintenance for pianos that weigh less than 150 kg,
or that a car rental company leases out cars of a certain make and model from a particular set of branches across the country.

Also, most if not all commercial and functional details of e-commerce scenarios can be expressed, e.g. eligible countries, payment and delivery options, quantity discounts, opening hours, etc.

The GoodRelations ontology is available under the Creative Commons Attribution 3.0 license. In a nutshell, you are free to copy, distribute and transmit the work; to remix/adapt the work (e.g. to import the ontology and create specializations of its elements), as long as you attribute the work.

GoodRelations is supported by Google, Yahoo, Bing, and Yandex as part of their schema.org initiative.

Project page and resources for developers

Project Page: http://purl.org/goodrelations/

Useful Links

Tools
GoodRelations-compliant product ontologies (extensions for specific types of products)
User's Guide work-in-progress
Cookbook work-in-progress
Specification in HTML and RDF/XML
Mailing list archive

Overview Materials

Webcast explaining the Web of Data for E-Commerce: http://www.heppnetz.de/projects/goodrelations/webcast/
Overview article on Semantic Universe: http://www.semanticuniverse.com/articles-semantic-web-based-e-commerce-webmasters-get-ready.html

Publications

Hepp, Martin: GoodRelations: An Ontology for Describing Products and Services Offers on the Web, Proceedings of the 16th International Conference on Knowledge Engineering and Knowledge Management (EKAW2008), Acitrezza, Italy, September 29 - October 3, 2008, Springer LNCS, Vol 5268, pp. 332-347.
The Technical Report is also useful for understanding the underlying conceptual choices, despite being outdated in many ways.

See http://wiki.goodrelations-vocabulary.org/Publications for additional publications.