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METHOD AND APPARATUS FOR
AUTOMATION OF DIRECTORY
ASSISTANCE USING SPEECH
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a method and apparatus for providing directory assistance, at least partially automata- 10 cally, to telephone subscribers.
2. Background Art
In known telephone systems, a telephone subscriber requiring directory assistance will dial a predetermined telephone number. In North America, the number will typically be 411 or 555 1212. When a customer makes such a directory assistance call, the switch routes the call to the first available Directory Assistance (DA) operator. When the call arrives at the operator's position, an initial search screen at the operator's terminal will be updated with information supplied by the switch, Directory Assistance Software (DAS), and the Operator Position Controller (TPC). The switch supplies the calling number, the DAS supplies the default locality and zone, and the TPC supplies the default language indicator. While the initial search screen is being updated, the switch will connect the subscriber to the operator.
When the operator hears the "customer-connected" tone, the operator will proceed to complete the call. The operator 3Q will prompt for locality and listing name before searching the database. When a unique listing name is found, the operator will release the customer to the Audio Response Unit (ARU), which will play the number to the subscriber.
Telephone companies handle billions of directory assis- 35 tance calls per year, so it is desirable to reduce labour costs by minimizing the time for which a directory assistance operator is involved. As described in U.S. Pat. No. 5,014,303 (Velius) issued May 7, 1991, the entire disclosure of which is incorporated herein by reference, a reduction can be 40 achieved by directing each directory assistance call initially to one of a plurality of speech processing systems which would elicit the initial directory assistance request from the subscriber. The speech processing system would compress the subscriber's spoken request and store it until an operator 45 position became available, whereupon the speech processing system would replay the request to the operator. The compression would allow the request to be replayed to the operator in less time than the subscriber took to utter it. Velius mentions that automatic speech recognition also 50 could be employed to reduce the operator work time. In a paper entitled "Multiple-Level Evaluation of Speech Recognition Systems", the entire disclosure of which is incorporated herein by reference, John F. Pitrelli et al disclose a partially automated directory assistance system in which 55 speech recognition is used to extract a target word, for example a locality name, from a longer utterance. The system strips off everything around the target word so that only the target word is played back to the operator. The operator initiates further action. go
U.S. Pat. No. 4,797,910 (Daudelin) issued Jan. 10, 1989, the entire disclosure of which is incorporated herein by reference, discloses a method and apparatus in which operator involvement is reduced by means of a speech recognition system which recognizes spoken commands to determine 65 the class of call and hence the operator to which it should be directed. The savings to be achieved by use of Daudelin's
speech recognition system are relatively limited, however, since it is not capable of recognizing anything more than a few commands, such as "collect", "calling card", "operator", and so on.
These known systems can reduce the time spent by a directory assistance operator in dealing with a directory assistance call, but only to a very limited extent.
SUMMARY OF THE INVENTION
The present invention seeks to eliminate, or at least mitigate, the disadvantages of the prior art and has for its object to provide an improved new directory assistance apparatus and method capable of reducing, or even eliminating, operator involvement in directory assistance calls.
To this end, according to one aspect of the present invention, there is provided directory assistance apparatus for use in a telephone system, comprising a voice processing unit having at least one lexicon of lexemes potentially recognizable by the unit and data representing a predetermined relationship between each of said lexemes and each of a plurality of call sources in an area served by the directory assistance apparatus. The unit also has means for issuing messages to a caller making a directory assistance call to prompt the caller to utter a required one of the lexemes, and means for detecting an identifier, for example a portion of a calling number, for the call source from whence the directory assistance call was received, means responsive to the identifier detected and to the data for computing a probability index for each lexeme representing the likelihood of that particular one of said lexemes being that uttered by the caller, and speech recognition means for selecting from the lexicon, on the basis of the acoustics of the caller's utterance and the probability index, a lexeme corresponding to that uttered by the caller.
A lexeme is a basic lexical unit of a language and comprises one or several words, the elements of which do not separately convey the meaning of the whole.
Preferably, the voice processing unit has several lexicons, each comprising a group of lexemes having a common characteristic, for example name, language, geographical area, and the speech recognition means accesses the lexicons selectively in dependence upon a previous user prompt.
Computation of the probability index may take account of a priori call distribution. A priori call distribution weights the speech recognition decision to take account of a predetermined likelihood of a particular locality containing a particular destination being sought by a caller. The apparatus may use the caller's number to identify the locality from which the caller is making the call.
The probability index might bias the selection in favour of, for example, addresses in the same geographical area, such as the same locality.
In preferred embodiments of the present invention the voice processing unit elicits a series of utterances by a subscriber and, in dependence upon a listing name being recognized, initiates automatic accessing of a database to determine a corresponding telephone number.
The apparatus may be arranged to transfer or "deflect" a directory assistance call to another directory assistance apparatus when it recognizes that the subscriber has uttered the name of a locality which is outside its own directory area. In such a situation, the above-mentioned predetermined relationship between the corresponding lexeme and the call source is that the lexeme relates to a locality which
is not served by the apparatus.
Thus, embodiments of the invention may comprise means for prompting a subscriber to specify a locality, means for detecting a place name uttered in response, means for comparing the uttered place name with the lexicon and in 5 dependence upon the results of the comparison selecting a message and playing the message to the subscriber. If the place name has been identified precisely as a locality name served by the apparatus, the message may prompt the caller for more information. Alternatively, if the locality name is Jq not in the area served by the apparatus, the message could be to the effect that the locality name spoken is in a different calling or directory area and include an offer to give the subscriber the directory assistance number to call. In that case, the speech recognition system would be capable of 15 detecting a positive answer and supplying the appropriate area code. Another variation is that the customer could be asked if the call should be transferred to the directory assistance operator in the appropriate area. If the subscriber answered in the afErmative, the system would initiate the 2o call transfer.
The caller's responses to the speech recognition system may be recorded. If the system disposed of the call entirely without the assistance of the operator, the recording could be erased immediately. On the other hand, if the call cannot be 25 handed entirely automatically, at the point at which the call is handed over to the operator, the recording of selected segments of the subscriber's utterances could be played back to the operator. Of course, the recording could be compressed using the prior art techniques mentioned above. 30
According to a second aspect of the invention, a method of at least partially automating directory assistance in a telephone system using directory assistance apparatus comprising a voice processing unit having a lexicon of lexemes potentially recognizable by the unit and data representing a 35 predetermined relationship between each of the lexemes and a calling number in an area served by the automated directory assistance apparatus, comprises the steps of:
issuing messages to a caller making a directory assistance call to prompt the caller to utter one or more utterances, 40 detecting an identifier, such as a calling number originating a directory assistance call, computing, in response to the identifier and said data, a probability index for each lexeme representing the likelihood that the lexeme will be selected, and employing speech recognition means to recognize, on 45 the basis of the acoustics of the caller's utterance and the probability index, a lexeme corresponding to that uttered by the caller.
Preferably, the voice processing unit has several lexicons, 5Q each having lexemes grouped according to certain characteristics e.g. names, localities, languages and the method includes the steps of issuing a series of messages and limiting the recognition process to a different one of the lexicons according to the most recent message. 55
The various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, in conjunction with the accompanying drawings, of a preferred embodiment of the invention. 60
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a general block diagram of a known telecommunications system;
FIG. 2 is a simplified block diagram of parts of a 65 telecommunications system employing an embodiment of the present invention;
FIGS. 3A and 3B are a general flow chart illustrating the processing of a directory assistance call in the system of FIG. 2;
FIG. 4 is a chart illustrating the frequency with which certain localities are requested by callers in the same or other localities; and
FIG. 5 is a graph of call distribution according to distance and normalized for population of the called locality.
BEST MODE FOR CARRYING OUT THE
FIG. 1 is a block diagram of a telecommunications system as described in U.S. Pat. No. 4,797,910. As described therein, block 1 is a telecommunications switch operating under stored program control. Control 10 is a distributed control system operating under the control of a group of data and call processing programs to control various parts of the switch. Control 10 communicates via link 11 with voice and data switching network 12 capable of switching voice and/or data between inputs connected to the switching network. An automated voice processing unit 14 is connected to the switching network 12 and controlled by control 10. The automated voice processing unit receives input signals which may be either voice or dual tone multifrequency (DTMF) signals and is capable of determining whether or not the DTMF signals are allowable DTMF signals and initiating action appropriately. In the system described in U.S. Pat. No. 4,797,910, the voice processing unit is capable of distinguishing between the various elements of a predetermined list of spoken responses. The voice processing unit 14 also is capable of generating tones and voice messages to prompt a customer to speak or key information into the system for subsequent recognition by the speech recognition system. In addition, the voice processing unit 14 is capable of recording a short customer response for subsequent playback to a human operator. The voice processing unit 14 generates an output data signal, representing the result of the voice processing. This output data signal is sent to control 10 and used as an input to the program for controlling establishment of connections in switching network 12 and for generating displays for operator position 24 coupled to the network 12 via line 26. In order to set up operator assistance calls, switch 1 uses two types of database system. Local database 16 is directly accessible by control 10 via switching network 12. Remote database system 20 is accessible to control 10 via switching network 12 and interconnecting data network 18. A remote database system is typically used for storing data that is shared by many switches. For example, a remote database system might store data pertaining to customers for a region. The particular remote database system 20 that is accessed via data network 18 would be selected to be the remote database associated with the region of the called terminal. Interconnecting data network 18 can be any well known data network and specifically could be a common channel signalling system such as the international standard telecommunications signalling system CCS 7.
A transaction recorder 22, connected to control 10, is used for recording data about calls for subsequent processing. Typically, such data is billing data. The transaction recorder 22 is also used for recording traffic data in order to engineer additions properly and in order to control traffic dynamically.
The present invention will be employed in a telecommunications system which is generally similar to that described in U.S. Pat. No. 4,797,910. FIG. 2 is a simplified block diagram of parts of the system involved in a directory assistance call, corresponding parts having the same reference numbers in both FIG. 1 and FIG. 2. As shown in FIG.