12. A method for extracting semantic information about a plurality of electronic documents autonomously created by different sources and being accessible via a computer network, comprising: accessing an electronic document via the computer network; generating a set of tokens by a computer, the tokens indicative of document object model (DOM) nodes associated with visual information in a displayed document image of the electronic document; deriving a non-prescribed visual grammar from the set of tokens by the computer, to represent a hidden syntax convention of visual presentation in the displayed document image; and applying said derived visual grammar by the computer to construct multiple parse trees that represent semantic structure of the electronic document and interpret a maximum subset of the set of tokens, wherein said non-prescribed visual grammar is derived from autonomous or heterogeneous Web documents to represent the hidden syntax convention of the visual presentation, and said derived non-prescribed visual grammar is a five tuple <Σ, N, s, Pd, Pf> where Σ is a set of terminal symbols, N is a set of nonterminal symbols, sεN is a start symbol, Pd is a set of production rules that represent visual patterns and Pf is a set of preference rules that represent pattern precedence.
12. A method for extracting semantic information about a plurality of electronic documents autonomously created by different sources and being accessible via a computer network, comprising: accessing an electronic document via the computer network; generating a set of tokens by a computer, the tokens indicative of document object model (DOM) nodes associated with visual information in a displayed document image of the electronic document; deriving a non-prescribed visual grammar from the set of tokens by the computer, to represent a hidden syntax convention of visual presentation in the displayed document image; and applying said derived visual grammar by the computer to construct multiple parse trees that represent semantic structure of the electronic document and interpret a maximum subset of the set of tokens, wherein said non-prescribed visual grammar is derived from autonomous or heterogeneous Web documents to represent the hidden syntax convention of the visual presentation, and said derived non-prescribed visual grammar is a five tuple <Σ, N, s, Pd, Pf> where Σ is a set of terminal symbols, N is a set of nonterminal symbols, sεN is a start symbol, Pd is a set of production rules that represent visual patterns and Pf is a set of preference rules that represent pattern precedence. 22. The method of claim 12 , wherein said Web documents are Web query forms.