Social Context for Offsite Advertisements

A social networking system associates one or more objects in the social networking system with a link to content external to the social networking system. This allows information about the object to be used as a proxy for information about the external content. An index associating objects in the social networking system with links to content external to the social networking system is maintained. A received link to external content are parsed into components, such as a domain name, a path, and a query string, and the components are compared to the index to identify an object associated with one or more of the comments of the received link. One or more rules may be applied to increase the likelihood of the identified object having similar subject matter as the external content.