book2

Best algorithm for LZW ..C language

instruction was spoken in the same format, with the same programmed pause
between the items.
A list of 58 instructions of the form shown above was recorded and used
to wire several pieces of apparatus without errors.
.sh "1.3  Telephone enquiry service"
.pp
The computer-generated wiring scheme illustrates how speech can be used to give
instructions without diverting visual attention from the task at hand.
The next system we examine shows how speech output can make the telephone
receiver into a remote computer terminal for a variety of purposes
(Witten and Madams, 1977).
.[
Witten Madams 1977 Telephone Enquiry Service
.]
The caller employs the touch-tone keypad shown in Figure 1.3 for input, and the
computer generates
a synthetic voice response.
.FC "Figure 1.3"
Table 1.3 shows the process of making
contact with the system.
.RF
.fi
.nh
.na
.in 0.3i
.nr x0 \w'COMPUTER:  '
.nr x1 \w'CALLER:  '
.in+\n(x0u
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Dials the service.
.ti-\n(x0u
COMPUTER:  Answers telephone.
"Hello, Telephone Enquiry Service.  Please
enter your user number".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters user number.
.ti-\n(x0u
COMPUTER:  "Please enter your password".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters password.
.ti-\n(x0u
COMPUTER:  Checks validity of password.
If invalid, the user is asked to re-enter
his user number.
Otherwise,
"Which service do you require?"
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters service number.
.in 0
.nf
.FG "Table 1.3  Making contact with the telephone enquiry system"
.pp
Advantage is taken of the disparate speeds of input (keyboard) and
output (speech) to hasten the dialogue by imposing a question-answer structure
on it, with the computer taking the initiative.  The machine can
afford to be slightly verbose if by so doing it makes the caller's
response easier, and therefore more rapid.  Moreover, operators who
are experienced enough with the system to anticipate questions can
easily forestall them just by typing ahead, for the computer is programmed
to examine its input buffer before issuing prompts and to suppress them if
input has already been provided.
.pp
An important aim of the system is to allow application programmers with no
special knowledge of speech to write independent services for it.
Table 1.4 shows an example of the use of one such application program,
.RF
.fi
.nh
.na
.in 0.3i
.nr x0 \w'COMPUTER:  '
.nr x1 \w'CALLER:  '
.in+\n(x0u
.ti-\n(x0u
COMPUTER:  "Stores Information Service.  Please enter
component name".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "SN7406#".
.ti-\n(x0u
COMPUTER:  "The component name is SN7406.  Is this correct?"
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "*1#" (system convention for "yes").
.ti-\n(x0u
COMPUTER:  "This component is in stores".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "*7#" (command for "price").
.ti-\n(x0u
COMPUTER:  "The component price is 35 pence".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "*8#" (command for "minimum number").
.ti-\n(x0u
COMPUTER:  "The minimum number of this component kept
in stores is 10".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "SN7417#".
.ti-\n(x0u
COMPUTER:  "The component name is SN7417.  Is this correct?"
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "*1#".
.ti-\n(x0u
COMPUTER:  "This component is not in stores".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "*9#" (command for "delivery time").
.ti-\n(x0u
COMPUTER:  "The expected delivery time is 14 days".
.ti-\n(x0u
CALLER:\h'\n(x0u-\n(x1u'  Enters "*0#".
.ti-\n(x0u
COMPUTER:  "Which service do you require?"
.in 0
.nf
.FG "Table 1.4  The Stores Information Service"
the
Stores Information Service, which permits enquiries to be made of a database
holding information on electronic components kept in stock.
This subsystem is driven by
.ul
alphanumeric
data entered on the touch-tone keypad.  Two or three letters are associated
with each digit, in a manner which is fairly standard in touch-tone telephone
applications.  These are printed on a card overlay
that fits the keypad (see Figure 1.3).  Although true alphanumeric data entry
would require a multiple key press for each character,
the ambiguity inherent in
a single-key-per-character convention can usually be resolved by the computer,
if it has a list of permissible entries.  For example, the component names
SN7406 and ZTX300 are read by the machine as "767406" and "189300", respectively.
Confusion rarely occurs if the machine is expecting a valid component code.
The same holds true of people's names, and file names \(em although with these
one must take care not to identify a series of files by similar names, like
TX38A, TX38B, TX38C.  It is easy for the machine to detect the rare cases
where ambiguity occurs, and respond by requesting further information:  "The
component name is SN7406.  Is this correct?"  (In fact, the Stores Information
Service illustrated in Table 1.4 is defective in that it
.ul
always
requests confirmation of an entry, even when no ambiguity exists.)  The
use of a telephone keypad for data entry will be taken up again in Chapter 10.
.pp
A distinction is drawn throughout the system between data entries and
commands, the latter being prefixed by a "*".  In this example, the
programmer chose to define a command for each possible question about a
component, so that a new component name can be entered at any time
without ambiguity.  The price paid for the resulting brevity of dialogue
is the burden of memorizing the meaning of the commands.  This is an
inherent disadvantage of a one-dimensional auditory display over the
more conventional graphical output:   presenting menus by speech is tedious and
long-winded.  In practice, however, for a simple task such as the
Stores Information Service it is quite convenient for the caller to
search for the appropriate command by trying out all possibilities \(em there
are only a few.
.pp
The problem of memorizing commands is alleviated by establishing some
system-wide conventions.  Each input is terminated by a "#", and
the meaning of standard commands is given in Table 1.5.
.RF
.fi
.nh
.na
.in 0.3i
.nr x0 \w'# alone  '
.nr x1 \w'\(em  '
.ta \n(x0u +\n(x1u
.nr x2 \n(x0+\n(x1
.in+\n(x2u
.ti-\n(x2u
*#	\(em	Erase this input line, regardless of what has
been typed before the "*".
.ti-\n(x2u
*0#	\(em	Stop.  Used to exit from any service.
.ti-\n(x2u
*1#	\(em	Yes.
.ti-\n(x2u
*2#	\(em	No.
.ti-\n(x2u
*3#	\(em	Repeat question or summarize state of current
transaction.
.ti-\n(x2u
# alone	\(em	Short form of repeat.  Repeats or summarizes
in an abbreviated fashion.
.ta 0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i
.in 0
.nf
.FG "Table 1.5  System-wide conventions for the service"
.pp
A summary of services available on the system is given in
Table 1.6.
.RF
.fi
.na
.in 0.3i
.nr x0 \w'000  '
.nr x1 \w'\(em  '
.nr x2 \n(x0+\n(x1
.in+\n(x2u
.ta \n(x0u +\n(x1u
.ti-\n(x2u
\0\01	\(em	tells the time
.ti-\n(x2u
\0\02	\(em	Biffo (a game of NIM)
.ti-\n(x2u
\0\03	\(em	MOO (a game similar to that marketed under the name "Mastermind")
.ti-\n(x2u
\0\04	\(em	error demonstration
.ti-\n(x2u
\0\05	\(em	speak a file in phonetic format
.ti-\n(x2u
\0\06	\(em	listening test
.ti-\n(x2u
\0\07	\(em	music (allows you to enter a tune and play it)
.ti-\n(x2u
\0\08	\(em	gives the date
.sp
.ti-\n(x2u
100	\(em	squash ladder
.ti-\n(x2u
101	\(em	stores information service
.ti-\n(x2u
102	\(em	computes means and standard deviations
.ti-\n(x2u
103	\(em	telephone directory
.sp
.ti-\n(x2u
411	\(em	user information
.ti-\n(x2u
412	\(em	change password
.ti-\n(x2u
413	\(em	gripe (permits feedback on services from caller)
.sp
.ti-\n(x2u
600	\(em	first year laboratory marks entering service
.sp
.ti-\n(x2u
910	\(em	repeat utterance (allows testing of system)
.ti-\n(x2u
911	\(em	speak utterance (allows testing of system)
.ti-\n(x2u
912	\(em	enable/disable user 100 (a no-password guest user number)
.ti-\n(x2u
913	\(em	mount a magnetic tape on the computer
.ti-\n(x2u
914	\(em	set/reset demonstration mode (prohibits access by low-priority users)
.ti-\n(x2u
915	\(em	inhibit games
.ti-\n(x2u
916	\(em	inhibit the MOO game
.ti-\n(x2u
917	\(em	disable password checking when users log in
.ta 0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i +0.8i
.in 0
.nf
.FG "Table 1.6  Summary of services on a telephone enquiry system"
They range from simple games and demonstrations, through serious database
services, to system maintenance facilities.
A priority structure is imposed upon them, with higher
service numbers being available only to higher priority users.
Services in the lowest range (1\-99) can be obtained by all, while
those in the highest range (900\-999) are maintenance services,
available only to the system designers.  Access to the lower-numbered
"games" services can be inhibited by a priority user \(em this was
found necessary to prevent over-use of the system!  Another advantage
of telephone access to an information retrieval system is that some
day-to-day maintenance can be done remotely, from the office telephone.
.pp
This telephone enquiry service, which was built in 1974, demonstrated that
speech synthesis had moved from a specialist phonetic discipline into the
province of engineering practicability.  The speech was generated "by rule"
from a phonetic input (the method is covered in Chapters 7 and 8), which
has very low data storage requirements of around 75\ bit/s of speech.
Thus an enormous vocabulary and range of services could be accomodated on a
small computer system.
Despite the fairly low quality of the speech, the response from callers was
most encouraging.  Admittedly the user population was a self-selected body of
University staff, which one might suppose to have high tolerance to new ideas,
and a system designed for the general public would require more effort to be
spent on developing speech of greater intelligibility.  Although it was
observed that some callers failed to understand parts of the responses, even
after repetition, communication was largely unhindered in most cases; users
being driven by a high motivation to help the system help them.
.pp
The use of speech output in conjunction with a simple input device requires
careful thought for interaction to be successful and comfortable.  It is
necessary that the computer direct the conversation as much as possible,
without seeming to be taking charge.  Provision for eliminating prompts
which are unwanted by sophisticated users is essential to avoid frustration.
We will return to the topic of programming techniques for speech interaction
in Chapter 10.
.pp
Making a computer system available over the telephone results in a sudden
vast increase in the user population.  Although people's reaction to a new
computer terminal in every office was overwhelmingly favourable, careful
resource allocation was essential to prevent the service being hogged by a
persistent few.  As with all multi-access computer systems, it is particularly
important that error recovery is effected automatically and gracefully.
.sh "1.4  Speech output in the telephone exchange"
.pp
The telephone enquiry service was an experimental vehicle for research on speech
interaction, and was developed in 1974.
Since then, speech has begun to be used in real commercial applications.
One example is System\ X, the British Post Office's computer-controlled
telephone exchange.  This incorporates many features
not found in conventional telephone exchanges.
For example, if a number is found to be busy, the call can be attempted
again by a "repeat last call" command, without having to re-dial the full number.