1. A diagnosis engine for estimating a status of an entity with a plurality of components which each is assumed to be in a fault-free mode or be in exactly one of at least one fault mode, the diagnosis engine comprising: a processing unit adapted to analyze test results; and at least one storage area adapted to store diagnostic data in respect of the entity, wherein said processing unit is adapted to: receive an original disjunction of diagnostic expressions indicating at least one of said modes for at least one of said components, receive first test results of a set of diagnostic tests in respect of the entity, the result of each test being a disjunction of statements wherein each statement indicates at least one of said modes for one of said components, store the expressions in the original disjunction of diagnostic expressions to a temporary disjunction of diagnostic expressions in a first storage area, investigate, for each diagnostic expression in the temporary disjunction of diagnostic expressions, whether a currently investigated diagnostic expression implies the first test result; if not so, remove the expression from the temporary disjunction of diagnostic expressions; and, for each statement in the first test result, generate a joint diagnostic expression representing a conjunction of the statement and the currently investigated diagnostic expression, compare the joint diagnostic expression with each diagnostic expression in the original disjunction of diagnostic expressions except for the currently investigated diagnostic expression, and, discard the joint diagnostic expression, if an original diagnostic expression is found, where the joint diagnostic expression implies the original diagnosis expression, or, add the joint diagnostic expression to an updated disjunction of diagnostic expressions in a second storage area, if an original diagnostic expression is not found, the updated disjunction of diagnostic expressions representing an estimated status of the entity, thereafter add all remaining diagnostic expressions in the temporary disjunction of diagnostic expressions to the updated disjunction of diagnostic expressions, and produce a status report based on the updated disjunction of diagnostic expressions.