16. A computer system for resolving ambiguities in date values associated with an attribute of an entity, the computer system comprising: one or more processors; memory; and one or more programs stored in the memory, the one or more programs comprising instructions to: obtain a first text string associated with an attribute of an entity, wherein the first text string is extracted from a first web document; determine if that the first text string conforms to one or more date formats; assign a first confidence value for each of the date formats for the first text string based on a first number of unknown variables that remain when interpreting the first text string using each of the date formats; obtain a second text string associated with the attribute of the entity, wherein the second text string is extracted from a second web document; determine if that the second text string conforms to one or more date formats; assign a second confidence value for each of the date formats for the second text string based on a second number of unknown variables that remain when interpreting the second text string using each of the date formats; determine a first date string expressed in a date format with a highest first confidence value for the first text string; determine a second date string expressed in a date format with a highest second confidence value for the second text string; and merge a first subset of the first date string and a second subset of the second date string to obtain a date value for the attribute.
18. The system of claim 16 , further comprising instructions to: determine whether the first text string is consistent with rules related to the attribute.