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(19) 



J 



Europaisches Patentamt 
European Patent Office 
Office europeen des brevets 



(12) 



(id EP0 871 172A2 

EUROPEAN PATENT APPLICATION 



(43) 


Date of publication: 


(51) Intel A G11B 20/12, G11B 27/28 




14.10.1998 Bulletin 1998/42 








Annliratinn numhpr 98302861 4 






(22) 


Date of filing: 14.04.1998 






(84) 


Designated Contracting States: 


(72) 


Inventor: Yoshida, Masaki 




AT BE CH CY DE DK ES Fl FR GB GR IE IT LI LU 




Shinagawa-ku, Tokyo 141 (JP) 




MC NL PT SE 








Designated Extension States: 


(74) 


Representative: Turner, James Arthur et al 




AL LT LV MK RO SI 




D. Young & Co., 








21 New Fetter Lane 


(30) 


Priority: 11.04.1997 JP 94212/97 




London EC4A 1DA (GB) 


(71) 


Applicant: SONY CORPORATION 








Tokyo 141 (JP) 







(54) Method and medium for recording digital data 



(57) A digital data recording method is provided 
where the efficiency of use of the recording medium 
storage area for recording data in a sequence is in- 
creased and a desired data can be retrieved at a higher 
speed. 

When a record n in an entity is terminated at the 
trailing end of a group N, a record n+1 following the 
record n is recorded in a group N+1. When a record n 



extends up to the group N+1 , a header H2' attributed to 
the group N and a front part of the record n as well as 
the preceding records 1 to n-1 are designated as anoth- 
er entity E2'. The remaining or rear part of the record n 
is designated as an entity E3 1 and recorded in the group 
N-1 as added with a header H3'. Then, the record n+1 
is designated as an entity E4 and recorded in the group 
N+1 as added with a header H4. 



H2 


ENTITY E2 (ETE) 


ENTIT 


H E3 (ETE) 
H3 




f ^ 






i 


1 


2 




n-1 


n 


i 
I 


n+1 








GROUP N 


GROUP (N+1) 





H2' 



CM 
< 
CM 



CO 

o 

CL 
LU 



ENTITY E2' 

* 



(SPE) 



n-1 



GROUP N 



(LPE) 



ENTITY E3' (ETE) 
H3' 

J. 



| n+1 



GROUP (N+1) 



FIG.10 



Printed by Jouve, 75001 PARIS (FR) 



1 



EP0 871 172 A2 



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Description 

The present invention relates to a digital data re- 
cording method for recording digital data on a recording 
medium and a digital data recording medium for saving 
digital data. 

One of apparatuses for recording and playing back 
digital data on recording mediums is known as a stream- 
ing tape drive. Such a streaming tape drive has as a 
large recording capacity as tens to hundreds megabytes 
although depending on the length of a magnetic tape 
used as a recording medium and is commonly used for 
backup storage of bulk data which has been saved on 
a mass recording medium such as a hard disk in a com- 
puter. The streaming tape drive is also used for saving 
image data which is often huge in quantity. 

The streaming tape drive is provided with a rotary 
head for driving in a helical scanning mode to record 
and play back a data on a magnetic tape of the 8-mm 
VTR format. One of conventional streaming tape drives 
is disclosed in PCT Application No. PCT/JP 96/02 345 
(filed on August 22, 1 996) by the same applicant. 

The streaming data drive employing a magnetic 
tape of the 8-mm VTR format as a recording medium 
includes an input/output interface such as a small com- 
puter system interface (SCSI) for data to be recorded or 
played back. 

In recording, data supplied e.g. from a host compu- 
ter is introduced via the SCSI interface to the streaming 
tape drive. The data may be carried in units of a fixed 
length of data group and if necessary, compressed by a 
known data compression method and temporarily saved 
in a buffer memory. The data released from the buffer 
memory is then supplied in units of a predetermined da- 
ta length termed a "group" to a record/playback system 
where it is recorded on a magnetic tape with a rotary 
head. 

In playback, the data saved on the magnetic record- 
ing tape is read out by the rotary head and also saved 
temporarily in a buffer memory. The data is released 
from the memory buffer and when having been com- 
pressed in the recording, expanded by a known expan- 
sion method before transferred via the SCSI interface 
to a host computer. 

It is constantly desired for the streaming tape drive 
or mass data record/playback apparatus to improve its 
storage efficiency in order to record more amounts of 
data on the given recording area of a magnetic tape as 
the recording medium. It is also essential that the data 
saved on the medium is accessed and read at as a high- 
er speed as possible. 

Various respective aspects of the invention are de- 
fined in the appended claims. 

Embodiments of the invention can provide a digital 
data recording method in which a magnetic tape used 
as the recording medium for recoding and/or playing 
back of data in sequences is increased in the efficiency 
of storage area usage and accessed at a higher speed 



to read desired one of the data therefrom and a digital 
data recording medium associated with the method. 

A digital data recording method, according to em- 
bodiments of the present invention, where a number of 

s process units of data composed of a plurality of com- 
pressed data transmission units produced by compress- 
ing fixed length transmission units of data and a diction- 
ary data unit indicative of the information of the com- 
pressed data transmission units are allocated to a series 

10 of recording units of a fixed length suited for a corre- 
sponding recording medium, comprises the steps of: ex- 
amining whether or not one of the compressed data 
transmission units in each process unit to be allocated 
to two adjacent recording units is terminated at the trail- 
's ing end of a preceding one of the two adjacent recording 
units for recording the process units into the recording 
units according to a result of the examination; when the 
compressed data transmission unit is terminated at the 
trailing end of the preceding recording unit, ending up 

20 the recording of the process unit at the trailing end and 
reconstructing and recording another process unit 
which carries the remaining of the compressed data 
transmission units of the current process unit into the 
other or succeeding one of the two adjacent recording 

25 units; and when the compressed data transmission unit 
is not terminated at the trailing end of the preceding re- 
cording unit ; ending up the recording of the process unit 
at the end of the compressed data transmission unit 
which extends over the trailing end of the preceding re- 

30 cording unit and reconstructing and recording another 
process unit which carries the remaining of the com- 
pressed data transmission units of the current process 
unit into the other or succeeding one of the two adjacent 
recording units. 

35 A digital data recording medium, according to em- 
bodiments of the present invention, where a number of 
process units of data composed of a plurality of com- 
pressed data transmission units produced by compress- 
ing fixed length transmission units of data and a diction- 

40 ary data unit indicative of the information of the com- 
pressed data transmission units are allocated and re- 
corded into a series of recording units of a fixed length, 
is characterized by: when one of the compressed data 
transmission units in each process unit to be allocated 

45 to two adjacent recording units is terminated at the trail- 
ing end of a preceding one of the two adjacent recording 
units, ending up the recording of the process unit at the 
trailing end and reconstructing and recording another 
process unit which carries the remaining of the com- 

50 pressed data transmission units of the current process 
unit into the other or succeeding one of the two adjacent 
t recording units; and when the compressed data trans- 
mission unit is not terminated at the trailing end of the 
preceding recording unit, ending up the recording of the 

55 process unit at the end of the compressed data trans- 
mission unit which extends over the trailing end of the 
preceding recording unit and reconstructing and record- 
ing another process unit which carries the remaining of 



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EP0 871 172 A2 



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the compressed data transmission units of the current 
process unit into the other or succeeding one of the two 
adjacent recording units. 

The invention will now be described by way of ex- 
ample with reference to the accompanying drawings, 
throughout which like parts are referred to by like refer- 
ences, and in which: 

Fig. 1 is a diagram showing a streaming tape drive; 
Figs. 2A to 2D are explanatory views showing dif- 
ferent data units; 

Fig. 3 is an explanatory view showing a data struc- 
ture of one partition; 

Figs. 4A and 4B are explanatory views showing a 
data structure of one track; 
Fig. 5 is an explanatory view showing a data struc- 
ture of one group; 

Figs. 6A to 6C are explanatory views of compress- 
ing the records of data and grouping compressed 
data; 

Fig. 7 is an explanatory view of allocating entities to 
the groups; 

Fig. 8 is an explanatory view showing an entity map 
structure of the entity; 

Fig. 9 is an explanatory view showing a convention- 
al digital data recording method; and 
Fig. 1 0 is an explanatory view showing a digital data 
recording method. 

Preferred embodiments of the digital data recording 
method and the digital data recording medium of the 
present invention will be described in more detail refer- 
ring to the accompanying drawings. 

The description starts with a streaming tape drive 
which is an embodiment of the present invention. 

Fig. 1 is a block diagram showing a primary part of 
the streaming tape drive. The streaming tape drive is of 
a helical scanning type for recording/playing back of da- 
ta on a tape cassette of the 8-mm VTR format. 

A rotary drum 1 1 includes, for example, two record- 
ing heads 12A and 12B and two playback heads 13A 
and 1 3B. The two recording heads 1 2A and 1 2B are ar- 
ranged with their gaps adjacent to each other and dif- 
ferent in the azimuth angle. This arrangement is identi- 
cal to that of the playback heads 1 3A and 1 3B. The ro- 
tary drum 1 1 is driven by a drum motor 1 4 for rotation at 
a constant speed and on which a magnetic tape 3 runs. 
The magnetic tape 3 is transferred by a tape running 
system including a capstan motor and pinch rollers not 
shown. 

A mechanical controller 17 is provided for control- 
ling the rotation of the unshown capstan motor or a reel 
motor and providing servo control over the drum motor 
14 and tracking control of the tape 3. The mechanical 
controller 17 is thus connected in two-way relationship 
with a system controller which controls the entire sys- 
tem. 

The streaming tape drive also includes a SCSI 20 



(small computer system interface) used as an input/out- 
put interface for data through which data is introduced 
in a sequence from a host computer 25 and transmitted 
to a compression/expansion circuit 21 . The data is car- 
s ried in units of a fixed data length called "record" ex- 
plained later. 

It may be possible in the system of the streaming 
tape drive to use an alternative mode for transmission 
of data in units of variable data length from the host com- 
puter 25. In this embodiment, the data is to be transmit- 
ted in units of a fixed data length of the record. 

An action of the streaming tape drive for recording 
a data of interest on the magnetic tape 3 is now ex- 
plained. 

The compression/expansion circuit 21 subjects the 
data of interest to a proper compression process. The 
compression/expansion of the compression/expansion 
circuit 21 may be carried out by any applicable method, 
e.g. LZ coding. 

The LZ coding comprises converting a set of char- 
acters into a specific code which is then saved in a dic- 
tionary, comparing each succeeding set of characters 
with the saved code, and when the set of characters 
matches with the code, converting the set into a code in 
the dictionary. If the set does not match with the existing 
code in the dictionary, it is converted into another code 
and saved in the dictionary. In this manner, each set of 
characters is converted into a coded form and thus com- 
pressed in the data size. 

When the input data e.g. of image from the host 
computer 25 is in a compressed form, it is not processed 
in the compression/expansion circuit 21 and transmitted 
directly. The determination of whether the compression 
process is performed or not may be executed using pre- 
determined settings or by the system controller 1 5 con- 
sidering a reference data supplied through the SCSI in- 
terface 20. 

The data of compressed form from the compres- 
sion/expansion circuit 21 is temporarily saved in a buffer 
memory 23 via a buffer controller 22. The data when 
released from the buffer memory 23 is transferred in 
units of the group of a fixed data length under the control 
action of the buffer controller 22 to a modulator/demod- 
ulator circuit 18. The unit of the group will be described 
later in more detail. 

The modulator/demodulator circuit 18 modulates 
the data to a format suited for magnetic recording which 
is then supplied to an RF amplifier 1 9. The compressed 
data is amplified by the RF amplifier 19, transferred as 
a recording signal to the recording heads 1 2A and 1 2B, 
and recorded on the magnetic tape 3. 

An action of the streaming tape drive for playing 
back the compressed data recorded on the magnetic 
tape 3 is also explained in brief. 

The compressed data recorded on the magnetic 
tape 3 is read out by the playback heads 1 3A and 1 3b, 
played back as an RF playback signal, amplified by the 
RF amplifier 19, and demodulated by the modulator/de- 



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20 



25 



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40 



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3 



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EP0 871 172 A2 



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modulator circuit 18. 

A demodulated form of the data from the modulator/ 
demodulator circuit 1 8 is temporarily saved in the buffer 
memory 23 by the control action of the buffer controller 
22 before supplied to the compression/expansion circuit 
21. 

The compression/expansion circuit 21 expands the 
data according to a control signal of the system control- 
ler 1 5. If the data is not of a compressed form, it is trans- 
mitted directly without the expansion process. 

An expanded form of the data from the compres- 
sion/expansion circuit 21 is delivered as a playback data 
from the SCSI interface 20 to the host computer 25 or 
another system. 

The unit of data for transmission, compression/ex- 
pansion, and recording/playback of digital data with the 
streaming tape drive is explained. 

Fig. 2 illustrates the unit of data to be recorded on 
the magnetic tape 3. 

As shown in Fig. 2A, the magnetic tape 3 is wound 
between two reels 2A and 2B e.g. in a tape cassette. 

In the streaming tape drive, the magnetic tape 3 
may be divided into segments called partitions as shown 
in Fig. 2B. The number of the partitions may be 256 at 
maximum. Each partition can have a quantity of data 
recorded and played back independently. 

The partition is divided into segments of a fixed 
length called the groups as shown in Fig. 2C. The data 
is recorded in the groups on the magnetic tape 3. A sin- 
gle group carries 20 frames of data and each frame con- 
sists of 2 tracks as shown in Fig. 2D. The group is thus 
composed of 40 tracks of the data. 

Fig. 3 shows a structure of the partition. The expla- 
nation is now based on one partition recorded on the 
magnetic tape 3. 

A leader tape is provided in the leading end of the 
magnetic tape and followed by a device area for loading 
and unloading of the tape cassette. The head of the de- 
vice area is known as physical beginning of tape 
(PBOT). 

The device area is joined by a system log area for 
storage e.g. of a history of usage of the data and a data 
area for storage of the data. The head of the system log 
area is known as logical beginning of tape (LBOT). 

A vender group area, wherein the information on a 
vender which produces and provides data is identified, 
is provided in the head of the data area, and data for 
several groups 1 to n is recorded on the magnetic tape. 
Subsequent to the last group n, end of data (EOD), 
which shows a termination of the partition, is provided. 
The last portion of the EOD area is known as logical end 
of tape (LEOT). 

The tailing end of the magnetic tape is termed phys- 
ical end of tape (PEOT). 

Fig. 4 illustrates structures of a block and the track. 

Fig. 4A is the structure of the block which is com- 
posed of a fixed length unit of 73 bytes including 1 byte 
of sync data A1 , 6 bytes of ID data A2, 2 bytes of error 



correction parity A3 for the I D data, and 64 bytes of main 
data A4. 

Fig. 4B shows the structure of the track which is 
composed of 471 blocks. The track is provided at both 

5 ends two margins A11 and A17 of 4 blocks each. Two 
automatic track following (ATF) areas A12 and A16 are 
allocated after the margin A11 and before the margin 
A17 respectively. There is provided another ATF area 
A14 in the middle of the track. Each of the ATF areas 

10 A1 2, A1 4, and A1 6 comprises 5 blocks. Two data areas 
A1 3 and A1 5 of 224 blocks each are provided between 
the ATF areas A1 2 and A1 4 and between the ATF areas 
A14and A16. 

Fig. 5 shows a structure of the group. As described, 

is the group is composed of 20 frames. Two of the 20 
frames of the group at the trailing end are parity frames 
C3 for error correction. Other parities C1 and C2 though 
not explained in detail may be arranged on the basis of 
one per track. 

20 in the recording of data on the magnetic tape, the 
data is recorded in a sequence from the first frame of 
each group as denoted by the arrow Ar1 . A data of group 
information table (GIT) indicative of the content of the 
group is saved in the 18th frame as scanned in the di- 

25 rection, denoted by the arrow Ar2, opposite to the direc- 
tion of data recording. This is followed by recording a 
data of block access table (BAT) for controlling each en- 
tity (or record) in the group. The entity as a unit of data 
will be explained later in more detail. 

30 GIT may be 40 bytes of a fixed length data. BAT 
includes 4 bytes of access entry determined by the con- 
tent of the group and may be a variable length data. For 
simplicity of the explanation, a combination of GIT and 
BAT is referred to as an index data hereinafter. 

35 A procedure from compression of the data and to 
recording on the magnetic tape in groups is now ex- 
plained in conjunction with the arrangement of the 
streaming tape drive shown in Fig. 1. 

The data introduced from the host computer 25 is 

40 transmitted in the unit of a fixed length data called a 
record to the streaming tape drive. The record may be 
composed of 512 bytes of data. 

If the input data needs not to be compressed by the 
compression/expansion circuit 21 , its records are direct- 

45 |y shifted to the groups which are stored on the magnetic 
tape 3. In the playback, the records of the data are read 
out from the magnetic tape 3 according to the index data 
of each group and transferred via the SCSI interface 20 
to the host computer 25. 

50 When the input data supplied in units of the record 
from the host computer 25 is compressed by the com- 
pression/expansion circuit 21 , it is turned in each record 
to a variable length data depending on the content of 
the record. This allows the compressed data not to be 

55 played back correctly if it has been recorded in the form 
of groups on the magnetic tape directly as described 
previously. It is thus necessary to modify the com- 
pressed data before dividing it into the groups. 



4 



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EP0 871 172 A2 



8 



Fig. 6 illustrates the conversion of the compressed 
data of a fixed length record format into the groups for 
recording on the magnetic tape. 

The fixed length records (each having a size e.g. of 
512 bytes) shown in Fig. 6A will be different from one 
another in the size when carry the compressed data in- 
troduced in a sequence and compressed in the stream- 
ing tape drive. If the fixed length records are directly 
shifted to the groups by the same manner as of not com- 
pressed data, they may fail to be played back correctly. 

For compensation, a number of the records carrying 
the compressed data is turned to a unit called an entity 
before being grouped. The entity composed of the 
records of the compressed data is constructed in the 
buffer memory 23 in response to a control command 
from the system controller 1 5 of the streaming tape drive 
shown in Fig. 1 . Although the entity is composed of four 
records in Fig. 6 ; it may be constructed with any number 
of the records. 

Fig. 6B shows a structure of the entity. An entity 
head indicative of the convent of the data is provided at 
the leading end of the entity and followed by the records 
of the compressed data. The entity head will be ex- 
plained later. 

Then, a number of the entities, e.g. E1 , E2, E3, E4, 
and E5, are grouped to a fixed length, as shown in Fig. 
6C. The access entry of BAT shown in Fig. 5 is accom- 
panied with each entity. Accordingly, the compressed 
data are stored in the groups on the magnetic tape 3. 

Fig. 7 illustrates allocation of the variable length en- 
tities to the fixed length groups. As shown in Fig. 7, when 
the data of the entities E11, E12, E13, E14, and E15 is 
grouped, the entities are classified into two types; one 
included in the group (E11, E12, or E14) and also the 
other (E1 3, E15, or E1 6) which extends over two or more 
consecutive groups. 

The entity of the former type is designated by BAT 
as an "entire entity". 

Also, the entity of the latter type which bridges be- 
tween the two groups ; e.g. E15, is designated with its 
front region as a "start part entity" and its rear region as 
a "last part entity". 

The entity of the latter type which extends over the 
three groups, e.g. E1 3, is designated with its first region 
as a "start part entity", its second region as a "middle 
part entity", and its third region as a "last part entity". 

A file mark is provided between the entities E14and 
El 5 which identifies the location of an interface between 
two data files. More specifically, the entities E14 and 
E15 are saved as two different data files respectively. 
Although not shown, a save set mark is flagged at the 
end of the data which has been recorded by a single 
(recording) operation. 

Each of the entities E 1 1 , E 1 4, and E 1 5 is accompa- 
nied at its leading end with a sign of "*" which represents 
an access point for identifying the start location of the 
first record in an entity with e.g. LBOT, the separator 
marks (including the file mark and the save set mark), 



or entity attributes having been modified. 

In the playback, the access point is identified thus 
allowing the data in the entity to be processed corre- 
sponding to the entity attributes. Simultaneously, theda- 

5 ta is accessed and read on the entity-by-entity basis 
from the magnetic tape 3 by referring to GIT and BAT 
before transferred via the SCSI interface 20 to the host 
computer 25. 

Fig. 8 shows an entity map structure of the entity. 

10 As shown, the entity includes a string of bytes, each 
byte having bit numbers 0 (LSB) to 7 (MSB). The data 
of each byte is numbered by numerals starting from ze- 
ro. 

The entity header shown in Fig. 6B is composed of 
15 8 bytes from the byte number 0 to the byte number 7. 
The byte number 0 carries a data of "header length" in- 
dicative of the length of the entity header data. For ex- 
ample, if the access point is located in the current entity, 
the recording starts with the byte number n which is de- 
fined by the header length. In this embodiment, a quan- 
tity of data to be saved is specified by n=8. 

The byte number 1 carries a data of "algorithm 
number". 

The byte numbers 2 to 4 save a data e.g. of "original 
record length" indicating the original data length of the 
record. As shown, the original record length is 512 
bytes. 

The remaining byte numbers 5 to 7 carry a data of 
"record count in this entity" showing the number of the 
records in the entity. The number of the records may 
include the file marks indicative of the interface between 
two data files and the save set marks indicative of the 
location of end of the recording action in the records. 

The bytes denoted by the byte number 8 and higher 
contain the data of the records and one entity is com- 
pleted. 

A procedure of allocating the entities of a variable 
length data unit to the groups of a fixed length data unit 
in the digital data recording method of the present in- 
vention is now explained with reference to comparisons. 
It is assumed that the entity composed of a header H1 
and records 1 to (n+1) of the compressed data is allo- 
cated to two consecutive groups N and N+1 . 

Fig. 9 illustrates a comparative example of digital 
data recording method where the entity E1 is allocated 
to two consecutive groups. It is assumed that the 
records 1 to n stored in the group N are of SPE (start 
part of entity) and the record n+1 stored in the group 
N+1 is of LPE (last part of entity). 

When the record n+1 is desired for playback, the 
header H1 carrying a data indicative of the record n+1 
is first accessed since the access action is based on a 
unit of the group and its data is used for reading out the 
data in the group N in a sequence from the record 1 to 
the record n. This requires an extra period of time for 
reading the other data than the required record data in 
the group N. 

Fig. 10 shows the digital data recording method of 



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EP0 871 172 A2 



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the present invention where the entity is allocated to two 
consecutive groups while eliminating the above draw- 
back. 

The system controller 15 examines whether the 
record of compressed data produced by the compres- 
sion/expansion circuit 21 is terminated at the end of a 
group or not before its action moves to the following 
steps. 

Fig. 10 (a) illustrates the record n in an entity E2 is 
terminated at the interface between the groups N and 
N+1 , i.e. the end of a preceding one of the two consec- 
utive recording units. Accordingly, the record n+1 follow- 
ing the record n is stored in the group N+1 . Simultane- 
ously, the records 1 to n stored in the group N and a 
header H2 carrying a data of the records 1 to n are des- 
ignated as ETE (entire entity) of the entity E2 and also 
the record n+1 stored in the group N+1 is designated as 
ETE of the entity E3. The entity E3 is then added with a 
header H3 carrying a data indicative of the record n+1 . 

Fig. 10 (b) shows the record n in an entity E2' is not 
terminated at the end of the group N but extends to the 
group N+1. Accordingly, the records 1 to n-1 stored in 
the group N, the record n of which portion is stored in 
the group N+1 , and a header H2' carrying a data of the 
records 1 to n are designated as STE of the entity E2'. 
Also, the rear part of the record n stored in the group 
N+1 is designated as LPE of the entity E2'. 

The record n+1 stored in the group N+1 is designat- 
ed as an entity E3 1 and a header H3 1 carrying a data 
indicative of the group N+1 is added to the entity E3'. 
When the entities have been modified as described 
above, the dictionary data used for the data compres- 
sion is cleared. 

According to the above mentioned method, the var- 
iable length entities are successfully shifted to the fixed 
length groups in the playback thus allowing any com- 
pressed data record carrying a desired data to be ac- 
cessed at a higher speed than of the conventional man- 
ner. 

More specifically, in the digital data recording meth- 
od shown in Fig. 10, the retrieving of a desired data, e. 
g. the record n+1 , can be implemented through directly 
accessing the header H3 or H3 1 which carries a data of 
the record n+1 . Therefore, the access to the group N for 
reconstruction of a dictionary data is not needed and the 
reading of the records 1 to n is omitted. Accordingly, as 
the period required for performing the access is elimi- 
nated, the retrieval of data for playback will be much 
speeded up. 

In a digital data recording method and a digital data 
recording medium according to the present embodi- 
ments, compressed data to be played back is divided 
into groups of a fixed length recording unit through re- 
constructing the data in the form of entities, each com- 
posed of a variable length data carrying a number of the 
groups, and assigning portions of each particular entity, 
which extends over two or more groups, as correspond- 
ing entities provided with their respective headers. This 



allows the efficiency of use of the storage area of the 
recording medium to be increased and any desired one 
of the stored data to be accessed and retrieved at a high- 
er speed. 

5 

Claims 

1 . A digital data recording method where a number of 
10 process units of data composed of a plurality of 

compressed data transmission units produced by 
compressing fixed length transmission units of data 
and a dictionary data unit indicative of the informa- 
tion of the compressed data transmission units are 
is allocated to a series of recording units of a fixed 
length suited for a corresponding recording medi- 
um, comprising the steps of: 

examining whether or not one of the com- 
20 pressed data transmission units in each proc- 

ess unit to be allocated to two adjacent record- 
ing units is terminated at the trailing end of a 
preceding one of the two adjacent recording 
units for recording the process units into the re- 
25 cording units according to a result of the exam- 

ination; 

when the compressed data transmission unit is 
terminated at the trailing end of the preceding 
recording unit, ending up the recording of the 
30 process unit at the trailing end and reconstruct- 

ing and recording another process unit which 
carries the remaining of the compressed data 
transmission units of the current process unit 
into the other or succeeding one of the two ad- 
35 jacent recording units; and 

when the compressed data transmission unit is 
not terminated at the trailing end of the preced- 
ing recording unit, ending up the recording of 
the process unit at the end of the compressed 
40 data transmission unit which extends over the 

trailing end of the preceding recording unit and 
reconstructing and recording another process 
unit which carries the remaining of the com- 
pressed data transmission units of the current 
45 process unit into the other or succeeding one 

of the two adjacent recording units. 

2. A digital data recording method according to claim 

1, wherein the another process unit reconstructed 
50 includes a dictionary data unit indicative of the in- 
formation of the compressed data transmission 
units and the dictionary data unit is cleared when- 
ever a further process unit is reconstructed. 

55 3. a digital data recording method according to claim 

2, wherein the recording medium is a tape-like re- 
cording medium and the recording unit has a data 
storage size of a plurality of recording tracks defined 



25 



30 



35 



40 



45 



6 



11 



EP0 871 172 A2 



on the tape-like recording medium. 

A digital data recording medium where a number of 
process units of data composed of a plurality of 
compressed data transmission units produced by s 
compressing fixed length transmission units of data 
and a dictionary data unit indicative of the informa- 
tion of the compressed data transmission units are 
allocated and recorded into a series of recording 
units of a fixed length, characterized by: 10 

when one of the compressed data transmission 
units in each process unit to be allocated to two 
adjacent recording units is terminated at the 
trailing end of a preceding one of the two adja- 15 
cent recording units, ending up the recording of 
the process unit at the trailing end and recon- 
structing and recording another process unit 
which carries the remaining of the compressed 
data transmission units of the current process 20 
unit into the other or succeeding one of the two 
adjacent recording units; and 
when the compressed data transmission unit is 
not terminated at the trailing end of the preced- 
ing recording unit, ending up the recording of 25 
the process unit at the end of the compressed 
data transmission unit which extends over the 
trailing end of the preceding recording unit and 
reconstructing and recording another process 
unit which carries the remaining of the com- 30 
pressed data transmission units of the current 
process unit into the other or succeeding one 
of the two adjacent recording units. 

A digital data recording medium according to claim 35 

4, wherein the another process unit reconstructed 
includes a dictionary data unit indicative of the in- 
formation of the compressed data transmission 
units and the dictionary data unit is cleared when- 
ever a further process unit is reconstructed. 40 

A digital data recording medium according to claim 

5, wherein the medium is a tape-like recording me- 
dium. 



50 



55 



EP0 871 172 A2 




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EP0 871 172 A2 




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EP0 871 172 A2 



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15