17. A system comprising: a database of contact entries of a user; memory and one or more processors operable to execute instructions stored in the memory, comprising instructions to: identify a document associated with a user, the document visited, sent, or received by the user; analyze text of the document according to one or more regular expressions to identify contact information in the document, the contact information including one or more of an alias, a phone number, an email address, an occupation, a uniform resource locator, and an address; determine an affinity measure associated with the document, the affinity measure indicative of an interest of the user in the document; and populate, based on the affinity measure satisfying a threshold, a contact entry of the database of contact entries of the user with one or more aspects of the contact information, the populating including associating one or more properties of the contact entry with corresponding of the aspects of the contact information in the database of contact entries; receive a query entered by the user at a client computing device; determine the contact entry is responsive to the query based on matching the query to at least one of the populated aspects of the contact entry; and provide information from the contact entry for display at the client computing device in response to the query.
17. A system comprising: a database of contact entries of a user; memory and one or more processors operable to execute instructions stored in the memory, comprising instructions to: identify a document associated with a user, the document visited, sent, or received by the user; analyze text of the document according to one or more regular expressions to identify contact information in the document, the contact information including one or more of an alias, a phone number, an email address, an occupation, a uniform resource locator, and an address; determine an affinity measure associated with the document, the affinity measure indicative of an interest of the user in the document; and populate, based on the affinity measure satisfying a threshold, a contact entry of the database of contact entries of the user with one or more aspects of the contact information, the populating including associating one or more properties of the contact entry with corresponding of the aspects of the contact information in the database of contact entries; receive a query entered by the user at a client computing device; determine the contact entry is responsive to the query based on matching the query to at least one of the populated aspects of the contact entry; and provide information from the contact entry for display at the client computing device in response to the query. 19. The system of claim 17 , wherein the instructions further include instructions to: analyze the document to identify a contact information change measure associated with the document, the contact information change measure indicative of likelihood of a recent change to the contact information; wherein the instructions to determine the affinity measure for the document include instructions to determine the affinity measure based on the contact information change measure.