12. A speech understanding method comprising: recognizing an input speech to produce a speech recognition result; performing morpheme analysis on a sentence corresponding to the speech recognition result, recognizing and extracting additional information, and performing syntax analysis; describing the hierarchy of the sentence based on the additional information and results of the morpheme analysis and the syntax analysis; performing class transformation on the sentence whose hierarchy has been described; marking, by a computer, optional expressions for the sentence that has undergone the class transformation, deleting meaningless expressions and the additional information, converting the sentence into its base form, deleting morphemic tags or symbols to determine a semantic representation; retrieving the determined semantic representation from an example-based semantic representation pattern database; and selectively producing a retrieved semantic representation depending on whether or not the determined semantic representation exists in the example-based semantic representation pattern database.
12. A speech understanding method comprising: recognizing an input speech to produce a speech recognition result; performing morpheme analysis on a sentence corresponding to the speech recognition result, recognizing and extracting additional information, and performing syntax analysis; describing the hierarchy of the sentence based on the additional information and results of the morpheme analysis and the syntax analysis; performing class transformation on the sentence whose hierarchy has been described; marking, by a computer, optional expressions for the sentence that has undergone the class transformation, deleting meaningless expressions and the additional information, converting the sentence into its base form, deleting morphemic tags or symbols to determine a semantic representation; retrieving the determined semantic representation from an example-based semantic representation pattern database; and selectively producing a retrieved semantic representation depending on whether or not the determined semantic representation exists in the example-based semantic representation pattern database. 15. The speech understanding method of claim 12 , wherein said performing class transformation includes: converting a noun into a hypernym class; converting synonyms from declinable words into a single word; assigning particles subject to phonological change due to a final consonant to the same class; and classifying numeric representations of time and amount by using automata.