Computing responses to semantic queries. A method includes accessing a plurality of objects that represent source code for an input program. The source code is transformed into a plurality of immutable objects that are structured such that the immutable objects can be used to derive any response as defined by the semantic rules about the source code. A query is received from a requestor requesting a semantic characteristic of the input program. The semantic characteristic is calculated. The semantic characteristic is returned to the requestor. The semantic characteristic is cached in a cache. Information describing a dependency between the cached semantic characteristic and one or more of the objects in the plurality of objects is stored.