Freebase API

Freebase/Metaweb queries and responses are encoded as JSON:

http://www.freebase.com/api/service/mqlread?queries={"qname":{"query":[{"symbol":"CD4","type":"/biology/gene","*":null}]}}

Null fields in the query determine which fields are returned in the response.

There's a Metaweb MQL Query Editor for trying out queries.