Information retrieval system with serial access data storage and random access data retrieval

An information retrieval system in which information is stored in digital form in a serial access device such as a digital VCR, the information being organized as a library of successive albums, each album having successive tracks of individually identifiable items of information, such as audio performances, subjects or events. A random access device, such as a compact disc player or magnetic hard disc drive, has stored therein a portion of a preselected track of each album and a brief introductory portion of each of the remaining tracks in each album. Both devices are coupled to a common data bus and are controlled by a programmable processor so that during search intervals of the serial access device to access a selected album or track read-out thereof is initiated by the random access device. When the serial access device is ready to access selected track or album, read-out is switched over thereto. In this way the required storage capacity of the random access device is minimized while still providing random access to any album and to any track in an already designated album.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the field of information storage and retrieval, 
and more particularly to an information retrieval system wherein 
information is stored in digital form in a serial access device such as a 
magnetic or optical tape recorder, and specified portions thereof can be 
retrieved by random access without having to await traversal of 
intervening portions of the recorded data. 
Such a system can, for example, provide real time random access to a 
specified track in a comprehensive library of albums of data tracks which 
represent respective audio performances or other identifiable items of 
information. 
2. Description of the Related Art 
A serial access data storage device such as a digital audio tape recorder 
operates at the normal audio data reproduction rate of 256 Kbps (kilobits 
per second). The play time for an album of 15 tracks, each track being an 
individual selection, is therefore 54 minutes. For a comprehensive library 
of, for example, 400 albums, the total play time would be 360 hours. Even 
though the search speed of such a recorder is typically 200 times the play 
speed, it could take almost 2 hours to access a specified track in a 
specified album of such a library. 
This long retrieval time can be alleviated by employing a storage device 
which operates at much higher than the audio data rate, such as a consumer 
digital video cassette recorder or VCR. Such a recorder has a playback 
rate of about 100 times the audio data rate, or 25 Mbps, and the search 
speed is about 200 times the playback rate. The storage capacity for 400 
albums would be 41.5 Gbytes, and the maximum access time, depending on the 
location to be addressed, ranges between 33.2-66.4 seconds. In such a 
recorder the recorded data is encoded for purposes of error correction and 
data compression, and so it would be used with an intermediate buffer 
memory to convert from the recorder data rate to the audio data rate and a 
decoder to decode the encoded data and recover the original audio data. 
The maximum access time of about 1 minute is, of course, a major 
improvement over the nearly 2 hour maximum access time of an audio tape 
recorder, but is still too slow to be convenient for most users. 
There are, of course, random access storage devices, for example compact 
disc players and magnetic hard disc drives as used in personal computers, 
which provide virtually immediate access to data at any storage address 
therein. However, the storage capacity of a typical magnetic hard disc is 
only about 1 Gbyte, far short of the over 40 Gbytes required for a 
comprehensive library of 400 albums as proposed. 
Obviously, it would be of significant advantage if a serial storage device 
of high capacity, such as a digital VCR, could be provided with random 
access capability. 
SUMMARY OF THE INVENTION 
The invention provides an information retrieval system which includes a 
high capacity serial access device, such as a digital VCR, and a 
relatively lower capacity random access device, such as a compact disc 
player or magnetic hard disc drive. Read-out from both devices is 
coordinated by a programmable processor, the data so read being provided 
over a common bus to a buffer memory for data rate conversion. A complete 
library of albums, each including a plurality of data tracks, is stored in 
the serial access device. In addition, stored in the random access device 
is a portion of one preselected track from each album, as well as a brief 
introductory interval of each of the remaining tracks in each album, so 
that all tracks of all albums are represented but not actually stored in 
the random access recorder. For a 400 album library as suggested above, 
there will be 660 Mbytes of data from preselected tracks and 134 Mbytes of 
data from non-preselected tracks, for a total of 794 Mbytes. This is well 
within the typical 1 Gbyte capacity of a magnetic hard disc drive. 
When a user indicates an album selection to the processor, the processor 
issues a command to both devices to access such album. Read-out by the 
random access device of the stored portion of the preselected track of the 
relevant album is initiated immediately, and before reproduction of that 
data (at the audio rate) has been completed, the serial access device will 
have reached the location therein of data from the remaining portion of 
the preselected track of the relevant album. The processor then switches 
access to the common bus over to the serial access device and read-out is 
continued therefrom. If the user indicates a track other than the 
preselected track in a previously designated album, the serial access 
device being already positioned at such album, the processor controls the 
random access recorder to read-out the brief introductory interval stored 
therein of the addressed track in such album. During reproduction thereof 
(again at the audio rate) the serial access device will have reached the 
storage location therein of the addressed track. That is detected by the 
processor, since both devices are then at corresponding track addresses, 
and the processor then switches access to the common bus over to the 
serial access device and read-out is continued therefrom. The result is 
that, as perceived by the user, the serial access device apparently 
provides random access availability because there is no delay in 
reproduction of his selection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, this conceptually shows storage in a serial access 
high speed device, such as a digital video cassette recorder (VCR), of a 
library of albums each of which includes a number of tracks, a track being 
an identifiable selection such as, for example, a particular audio 
performance, event, or subject. For simplicity of illustration only 10 
albums are shown, each having 8 tracks, but the arrangement is the same 
for a larger library. The length of each track corresponds to the amount 
of recorded digital information, or data therein. Assuming the information 
to be audio, the track length will be proportional to the play time of the 
data thereon at the normal audio data rate of 256 Kbps. That will 
typically be 3.6 minutes for one selection of a typical compact disc 
recording. The recorder is bidirectional, and the pickup head may be 
situated anywhere on the recording medium, e.g. a magnetic or optical 
tape, when a command is issued for the pickup head to access a specified 
album and/or specified track. The recording medium will be hereinafter 
referred to as a tape. The compilation of albums constituting the library 
would typically be produced by recording on the tape digital data 
corresponding to a collection of individual albums such as audio compact 
discs or audio tapes. 
The access time, or "worst case" search time, of the pickup head to a 
specified data location on the tape ranges from a maximum for data located 
at either end of the tape, since the pickup head could be at the opposite 
end of the entire tape, to a minimum for data located at the center of the 
tape, since the pickup head then cannot be more remote than half of the 
entire tape. Using the example given above, of a library of 400 albums and 
15 tracks per album, a consumer digital VCR which operates at 25 Mbps, and 
recorded data which is audio information having a normal audio playback 
rate of 256 Kbps, the relevant parameters of the serial access recorder 
are then as shown in the following Table 1: 
TABLE 1 
______________________________________ 
SERIAL ACCESS (VCR) DEVICE 
No. of Albums 400 
Total Play Time (Audio 
360 hours (54 mins) per album 
Playback) 
Required VCR capacity 
41.5 Gbytes 
Long distance search speed 
200 .times. 25 Mbps = 5 Gbps 
Album access time 
33.2-66.4 sec. (depending on 
album position on tape) 
Short distance search speed 
33 .times. 25 Mbps = 825 Mbps 
Track access time in pre- 
0.5-1 sec. (depends on track 
selected album location in album) 
______________________________________ 
It is seen that the access time (worst case search time) to a specified 
album is between about one-half and one minute, and is between one-half 
and 1 second to a specified track in a preselected album. The maximum 
access time to an album is derived as follows: 
EQU 41.5 Gbytes.times.8 bits/byte.div.5 Gbps=66.4 secs. 
That would be for an album at either end of the tape. The minimum album 
access time would be for an album at the center of the tape, and so is 
half the maximum or 33.2 seconds. 
The maximum access time for a track within a preselected album is derived 
as follows: 
EQU 256 Kbps.times.60 sec/min.times.54 min/album=829 Mbits/album 
EQU 829 Mbits.div.825 Mbps=1 sec. 
That would be for a track at either end of the preselected album. For a 
track at the center of such album, the access time would be half of that 
value, or 0.5 sec. 
It will be noted that the audio play time of a track is 3.6 minutes, which 
exceeds the maximum access time of 66.4 seconds to any album. This is 
significant because, as will be described below, it is thereby possible to 
complete access to an album by the serial recorder within the play time of 
a portion of a preselected track in such album played at the normal audio 
data rate. 
FIG. 2 illustrates how, by using a random access device such as, for 
example, a compact disc player or magnetic hard disc drive, to supplement 
the serial access device, it is possible by storing only a limited amount 
of data in the random access device to achieve apparent continuous 
read-out of data stored in the serial access device. That is, in 
accordance with the invention, the random access device only need store 
enough data so that the play time of a stored portion of a data track at 
the normal reproduction rate will at least equal the access time of the 
serial access device to the remaining portion of such track. Once that 
condition has been reached, read-out can be continued from the serial 
access device. Seamless transition is achieved by assembling all the data 
in a buffer memory which serves to convert the data therein to the normal 
reproduction rate, e.g. the audio rate of 256 Kbps. 
As seen in FIG. 2, an introductory portion of one preselected track from 
each album is stored in the random access device. This will usually be the 
first of such tracks since that simplifies operation, but any track could 
be preselected in each album. The portion so stored is much less than the 
complete track, since as noted above the maximum access time of the serial 
access device to any album is 66.4 secs., as compared with a play time of 
3.6 minutes for the complete track. The random access device thus provides 
virtually immediate random access to the preselected track of any of the 
albums stored in the serial access device. Thus, instead of having to 
store all tracks in their entirety as shown in FIG. 1, portions of only 
certain of such complete tracks, one from each album, are stored in FIG. 
2. During reproduction at the normal reproduction rate of data from the 
portion of a preselected track stored as shown in FIG. 2 from any 
particular album, the serial access device will have had time to access 
and continue with read-out of the remaining portion of such track of such 
album, and further continues with read-out of the remaining tracks of that 
album. 
FIG. 2 also shows storage in the random access device of an even more brief 
introductory portion of each of the non-preselected tracks in each album, 
the duration thereof corresponding to the short distance maximum access 
time of the serial access device from any track in such album to any other 
track in the same album. As shown in Table 1, the maximum access time 
within an album is 1 second. Therefore, storing a portion corresponding to 
1 second play time (at the audio rate) of each non-preselected track in 
each album would be sufficient to enable the serial access device to 
access any non-preselected track of an album after having already been 
positioned for read-out from such album. 
As seen in Table 1, the access time both for a particular album and for a 
particular track varies from a maximum for data located at either end of 
the entire tape and at either end of each album, to a minimum for data 
located at the center of the tape and at the center of each album. The 
minimum access time is half the maximum access time. It is therefore 
possible, instead of recording the same portions of the tracks in each 
album, to use an adaptive allocation of the amount of data stored in the 
random access device depending on the location of the relevant album and 
track on the tape of the serial access device. Such an adaptive allocation 
is shown in FIG. 3, wherein, supposing the first track of each album as 
the preselected track to be stored, approximately equal portions of the 
preselected tracks of the first and last albums are stored, only half as 
much of the preselected track of the album at the center of the tape is 
stored, and for intermediate albums proportionate fractions of the 
preselected tracks therein are stored. A similar adaptive allocation is 
used for the non-preselected tracks in each album. Thus, in each album, 
the stored portions of the first and last of the non-preselected tracks 
are equal and correspond to the maximum access time within an album of the 
VCR as described above. The stored portion of the center track is half 
that of the first and last non-preselected tracks. For intermediate tracks 
proportionate fractions thereof are stored. Thus, the amount of data 
required to be stored in the random access device is reduced to the 
minimum necessary in order to correspond with the access times of the VCR 
for read-out of a specified album or to a specified track in a previously 
designated album. 
The following Table 2 summarizes the relevant parameters of a random access 
device as described, such as a hard magnetic disc (MD) drive, for use with 
a serial access VCR having the parameters shown in Table 1. The access 
times of the VCR, as shown in Table 1, are repeated here because they are 
determinative of the amount of data required to be stored in the random 
access recorder. All of the other parameters applicable to Table 1, i.e., 
an audio data rate of 256 Kbps, a VCR data rate of 25 Mbps, and 400 albums 
of 15 tracks each, are also applicable in Table 2. 
TABLE 2 
______________________________________ 
RANDOM ACCESS (MD) DEVICE 
Album access time of VCR 
33.2-66.4 sec. 
Data on MD from a pre- 
1.1-2.2 Mbytes/album (depends on 
selected track in an 
album on tape) 
album 
Total data on MD (pre- 
660 Mbytes 
selected tracks) 
Track access time of VCR 
0.5-1 secs. (depends on data 
within an album location in album) 
Data on MD from non- 
336 Kbytes/album 
preselected tracks/album 
Total data on MD (non- 
134 Mbytes 
preselected tracks) 
MD memory capacity 
660 + 134 = 794 Mbytes 
______________________________________ 
These entries are explained as follows. An interval of 33.2 sec. 
corresponds at the normal audio data rate to 
EQU 33.2 sec..times.256 Kbps.times.1/8 bytes/bit=1.03.apprxeq.1.1 Mbytes 
The range of 1.1-2.2 Mbytes/album is an average of 1.65 Mbytes/album for 
all 400 albums, and so the data from non-preselected tracks is 
EQU 1.65.times.400=660 Mbytes. 
The range of 0.5-1 secs. track access time averages to 0.75 secs. for all 
14 non-preselected tracks in each album. The required data from such 
tracks on the FED is therefore 
EQU 0.75.times.14.times.256 Kbps.times.1/8 bytes/bit=336 Kbytes/album 
For 400 hundred albums, the non-preselected track data is therefore 
400.times.336=134 Mbytes. Combining that with the 660 Mbytes required for 
the preselected track data, the necessary capacity of the magnetic disc 
recorder is 660+134=794 Mbytes. That is well within the one Gbyte capacity 
of inexpensive hard magnetic disc drives. 
FIG. 4 is a block diagram of an information retrieval system in accordance 
with the invention for operation as described above. The serial access 
device 1 is a digital VCR having the characteristics shown in Table 1, 
operating at 25 Mbps. A library of audio or other information to be 
stored, in the form of successive albums each containing a plurality of 
tracks, is recorded in digital form on the VCR tape. The normal 
reproduction rate of the stored information is substantially slower than 
the operating rate of the VCR. For audio information the audio 
reproduction rate is 256 Kbps. 
The VCR 1 and a random access device 2, for example a magnetic hard disc 
drive (MD) as suggested above, are both coupled to a data bus 3 to which 
is also coupled a programmable data processor which coordinates operation 
of both storage devices and access thereof to the data bus at appropriate 
intervals in order to provide data for continuous reproduction. The data 
provided to the bus is conveyed thereby to a digital first-in-first-out or 
FIFO memory 5, which is controlled by processor 3 to provide output of 
data at the desired reproduction rate, in the case of audio data 256 Kbps. 
Memory 5 supplies the data at the audio rate to a decoder 6 for decoding 
and D/A conversion. The resultant signal is supplied to a reproduction 
facility, shown in this case as a pair of stereo loud speakers. 
Initially the storage devices are controlled by processor 3 to record in 
the MD device 2 the necessary portions of data tracks of the albums 
already recorded in the VCR 1, so that the stored data in MD device 2 will 
be sufficient for CPU 4 to maintain memory 4 at a filling level which 
assures a continuing flow of data at the audio rate to decoder 5 during 
intervals when VCR 1 is still searching to access a designated album or 
track. From the description given above it will now be apparent how that 
is achieved. An introductory portion of a selected track, preferably the 
first, of the first album in VCR 1 is also recorded in MD device 2. A 
lesser introductory portion of each succeeding track in the first album in 
VCR 1 is then also successively recorded in MD device 2, such portion 
linearly decreasing from the second track to the central track so that the 
duration of the recorded portion of the central track is approximately 
half that of the second track, and then linearly increasing for succeeding 
tracks so that the duration of the stored portion of the last track is the 
same is that of the second track. This procedure is then repeated for the 
second and succeeding albums, with similar provision for adaptive 
allocation of the stored portion of the preselected track of each album. 
That is, the stored portion of preselected tracks in albums succeeding the 
first album linearly decreases up to the predetermined track of the album 
at the center of the library, for which the stored portion of the 
predetermined track thereof is approximately half that of the 
predetermined track in the first album. For albums succeeding the central 
album this procedure is reversed, the stored portions of the predetermined 
tracks of the succeeding albums linearly increasing until for the last 
album the stored portion of the predetermined track thereof is 
approximately the same as for the first album. 
It shall be noted that, although coding is not a novel feature of the 
present invention, the data recorded in the VCR 1 may not be the original 
audio data to be reproduced but my have been encoded to provide for 
compression and error correction. 
After the necessary data has thus been recorded in the random access MD 
device, the system is ready for operation as a random access library. It 
should be understood that random access is provided to any album and also 
to any track in an already designated album, but not to any track of any 
newly designated album. This is dealt with further below. Using the 
processor 4 the user specifies a particular album or albums and tracks 
thereon to be played. The processor controls the VCR 1, via a conventional 
selection unit thereof, to commence search to access the indicated 
choices, and simultaneously switches access to the data bus 3 to MD device 
2 so that playback is commenced therefrom in accordance with the first of 
such choices; e.g., a chosen album. It is assumed that the user has 
already made a designation of a track, such as the first track, in each 
album as the preselected track thereof. The MD device 2 is controlled by 
processor 4 to read-out via bus 3 to buffer memory 5 the stored data 
corresponding to a portion of the first track in the chosen album, and 
such data is then read-out from memory 5 to decoder 6 at the normal audio 
rate, subjected thereby to decoding and D/A conversion, and the resulting 
signal is supplied to the loudspeakers. While that is occurring, the VCR 1 
accesses the chosen album and the preselected track therein. The track 
address of the data at the pickup head of VCR 1 is monitored by processor 
4, which also monitors the address in MD device 2 of data supplied thereby 
to buffer memory 5. When such addresses correspond to the same data, that 
means that the pickup head of VCR 1 is in position to continue read-out of 
a track from where MD device 2 has just left off. The processor 4 then 
switches access to data bus 3 over to the VCR 1, and playback of the 
preselected track of the chosen album is continued with data supplied from 
that recorder. 
In the event the user has chosen a particular track of a particular album 
other than the preselected track thereof, there are two alternative 
procedures available. The first alternative is to begin with playback of 
the preselected track of such album, followed without any interruption by 
playback of the chosen track in that album. This proceeds substantially as 
described above, except that after completion of read-out of the 
preselected track of such album the processor 4 controls MD device 2 to 
read-out the stored introductory portion of the chosen track in such 
album. Once the VCR 1 is ready to access the remainder of such track the 
processor 4 switches access to data bus 3 over to VCR 1 and read-out of 
the chosen track is continued therefrom. The second alternative, which the 
user can signify to processor 4, is to wait out the access time (between 
1/2 and 1 minute, see Table 2) for VCR 1 to reach the album which contains 
the chosen track. In that event the processor does not switch access to 
the data bus to MD device 2 until that occurs, after which MD device 2 is 
given access to data bus 3 to read-out the portion of the chosen track 
stored therein. By then VCR 1 will be in position to access that track and 
operation resumes as described above for the first alternative. 
Although the invention has been described with reference to certain 
preferred embodiments thereof, it will be apparent to those skilled in the 
art that various modifications and adaptations thereof can be made without 
departing from the essential scope and teachings of the invention as set 
forth in the ensuing claims.