21. The computer-implemented method of claim 2 , wherein each respective grammar transformations (G→G′) i in the first sequence of grammar transformations is invertible by a corresponding grammar transformation (G′→G) i , in a second sequence of grammar transformations {(G′→G) 1 , . . . , (G′→G) n }, that undoes an effect of the transformation (G→G′) i with respect to the domain grammar, and the instructions to transform information comprise using the second sequence of grammar transformations to structurally transform information extracted from the second set of source documents to the format of the domain grammar.
2. The non-transitory computer readable storage medium of claim 1 , wherein the instructions to select the page grammar for the first set of source documents comprises heuristically identifying a first sequence of grammar transformations {(G→G′) 1 , . . . , (G→G′) n } that transforms the domain grammar to the page grammar.