Semantic grammars encode semantic information into a syntactic grammar. They use context free rewrite rules with non terminal semantic constituents. Generally a semantic error occurs when the meaning of the knowledge is not properly communicated. Semantic errors occur if the human expert misinterprets the knowledge engineerâ€™s question or answers inappropriately. The proper constituents of semantic grammar are noun phrase (NP), verb phrase (VP), Noun (N), Verb (V), Preposition phrase (PP), Adverb (ADV) and so on. One of the successful applications of semantic grammar is the LIFER system (A database query system). In the LIFER system, there are several rules to handle the wh-queries such as:
What is the name of your country?
Which department of your country is must efficient?
Who guide them?
Where they are being guided?
These sentences are analyzed and words matched to the symbols contained in the lexicon entries. Semantic grammars are suitable for use in systems with restricted grammars since its power of computation is limited.