Methods, systems, and apparatus, including computer programs encoded on computer storage media, for implementing a resolver service. One of the methods includes: obtaining event data from a blockchain, wherein the event data comprises a plurality of updates associated with a plurality of decentralized identifier (DID) documents stored on the blockchain; storing the event data in a database; receiving a request for information associated with the event data; and providing information about one or more updates associated with one or more of the DID documents in response to the request.