5. A computer-implemented method for determining dialog states of utterances comprising: receiving a given utterance of a dialog session, the given utterance represented as computer readable text; identifying a sub-string of the computer readable text for string-matching to a slot-value pair of an ontology; determining, by the string-matching, a successful match between the sub-string and a string that represents a synonym of a value of the slot-value pair to identify the slot-value pair associated with the utterance by identifying the synonym in the utterance; adding the slot-value pair to a candidate dialog state of the given utterance based on the successful match, wherein the candidate dialog state comprises a candidate set of slot-value pairs assigned to the given utterance; assigning a predicted dialog state to the given utterance in a history of dialog states of the dialog session based on the candidate dialog state; and outputting a response to the given utterance to a user device of a user associated with the given utterance based on the predicted dialog state.
5. A computer-implemented method for determining dialog states of utterances comprising: receiving a given utterance of a dialog session, the given utterance represented as computer readable text; identifying a sub-string of the computer readable text for string-matching to a slot-value pair of an ontology; determining, by the string-matching, a successful match between the sub-string and a string that represents a synonym of a value of the slot-value pair to identify the slot-value pair associated with the utterance by identifying the synonym in the utterance; adding the slot-value pair to a candidate dialog state of the given utterance based on the successful match, wherein the candidate dialog state comprises a candidate set of slot-value pairs assigned to the given utterance; assigning a predicted dialog state to the given utterance in a history of dialog states of the dialog session based on the candidate dialog state; and outputting a response to the given utterance to a user device of a user associated with the given utterance based on the predicted dialog state. 14. The computer-implemented method of claim 5 , further comprising: identifying a historic slot-value pair in the history of dialog states for at least one utterance that occurs prior to the given utterance in the dialog session; determining the identified historic slot-value pair has a same slot as an existing slot-value pair in the candidate dialog state and a different value than the existing slot-value pair; based on the determining of the identified historic slot-value pair, refraining from including the historic slot-value pair in the predicted dialog state of the given utterance.