1. A data management system, comprising: a database, the database storing information, a subset of the stored information comprising annotated values, each annotated value having a stored data value and an associated data reliability value, wherein the data reliability value is a member of a domain that includes at least three distinct data reliability values corresponding to at least three distinct data reliability classifications that can apply to the annotated values stored in the database; and a query executer for executing queries requesting access to information stored in the database; the query executer including annotated nullable logic for evaluating expressions containing at least one annotated value as an operand, wherein the annotated nullable logic includes logic for combining annotated values, for comparing annotated values so as to generate annotated truth values, and for combining annotated truth values in accordance with a predefined set of rules and so as to preserve relevant ones of the data reliability values associated with the annotated values and annotated truth values that have been combined and compared; wherein the annotated nullable logic includes logic for combining first and second annotated values (k, A) and (m, B) using a predefined operator OP to generate an annotated result value (r, C): k, A) Op (m, B)=(r, C) where k, m and r represent data values or truth values, and A, B and C represent data reliability values associated with the annotated first, second and result values, respectively; and C is generated by the annotated nullable logic by combining A and B.