1. A computer implemented method for assigning codes from a standard lexicon to a free text document describing physical or tangible objects, the method comprising the steps of: (a) automatically segmenting said free text document into a plurality of sentences; (b) using a computer processor to retrieve a plurality of propositions by matching said sentences in a semantic mapping table created by domain experts through semantically annotating sentences from a corpus of related documents in a knowledge domain to propositions, (c) using a computer processor to retrieve a plurality of codes in a standard lexicon by matching said propositions to said codes created by a third party, in a code mapping table created by domain experts by annotating said propositions to said codes; wherein one or more of said matching codes from said standard lexicon represents at least a portion of the semantic content of said free text document.