EP0286719A2
Expired / Lapsed
EP
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Text compression and expansion method and apparatus
Assignee: International Business Machines Corp
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Filing: 1987-10-02
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Granted: —
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Expires: 2007-10-02
Abstract
Abstract A text compression method and apparatus are disclosed that enable overall compression ratios of more than six or eight to one for normal language text. Plural multiple-word dictionaries that are specialized for the particular field of use are employed together with a header transmission format that identifies which dictionaries are to be used. In addition, entries in these dictionaries are categorized by a weighted frequency of use ranking in which the product of the word length in characters and the frequency of occurrence of that word in the text is taken as the weighted figure of merit for ranking words to be placed in the individual dictionaries.
Inventors
- 👤 Ronald Jay Lisle
- 👤 Eual Aaron Moss
- 👤 John Hoyt Ryder
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 18:58
CPC Classifications
G; G06; G06F; G06F40/00; G06F40/10; G06F40/12; H; H03; H03M; H03M7/00; H03M7/30; H03M7/40; H03M7/42
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
110 words
A method of data compression, comprising characterized in that it comprises the steps of: separating an uncompressed coded data stream into units; comparing said units against at least one user selected dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed encoded units; outputting a compressed data header comprising indications for defining the identity of each of said user selected dictionaries used in compressing said data; and outputting the compressed code equivalents for incoming units for which a true comparison is found in said comparing step and outputting the uncompressed encoded character stream for any said unit for which no true comparison is found.
Claim 2
Independent Claim
110 words
A method of data compression, comprising characterized in that it comprises the steps of: separating an uncompressed coded data stream into units; comparing said units against at least one user selected dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed encoded units; outputting a compressed data header comprising indications for defining the identity of each of said user selected dictionaries used in compressing said data; and outputting the compressed code equivalents for incoming units for which a true comparison is found in said comparing step and outputting the uncompressed encoded character stream for any said unit for which no true comparison is found.
Claim 3
Dependent Claim
54 words
A method as described in Claim 1 characterized in that it comprises the step of arranging the entries in said dictionaries for said units in an order of merit established by multiplying the average frequency of occurrence of each said unit in the language in which it is used by its length in characters.
Claim 4
Independent Claim
132 words
A method of data compression, characterized in that it comprises the steps of: separating an incoming uncompressed encoded data stream into units; comparing said units against at least one user selected compiled dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed units; outputting a compressed data header comprising indications for defining the identity of each said user selected dictionary used in compressing said data; and outputting the compressed code equivalents for incoming units for which a true comparison is found in said comparing step and outputting the uncompressed encoded character stream for any said unit for which no true comparison is found; separating said uncompressed stream output from said compressed portions of said stream output by compression escape signals surrounding said uncompressed stream output portion.
Claim 5
Independent Claim
132 words
A method of data compression, characterized in that it comprises the steps of: separating an incoming uncompressed encoded data stream into units; comparing said units against at least one user selected compiled dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed units; outputting a compressed data header comprising indications for defining the identity of each said user selected dictionary used in compressing said data; and outputting the compressed code equivalents for incoming units for which a true comparison is found in said comparing step and outputting the uncompressed encoded character stream for any said unit for which no true comparison is found; separating said uncompressed stream output from said compressed portions of said stream output by compression escape signals surrounding said uncompressed stream output portion.
Claim 6
Dependent Claim
49 words
A method as described in Claim 3 characterized in that it said unit entries in said compiled dictionaries are arranged in order of merit established by multiplying the average frequency of occurrence for each said unit in the language in which it is used by its length in characters.
Claim 7
Independent Claim
42 words
A method as described in Claims anyone of Claims 1 to 4, wherein: at least one of said dictionaries comprises a control table of entries comprising segment identifiers for each segment of each said user selected dictionary used in compressing said data.
Claim 8
Independent Claim
36 words
A method as described in anyone of Claims to 5, characterized in that: said dictionaries are assigned to byte addressable memory locations in a computer memory access system having memory addresses in integral whole number bytes.
Claim 9
Independent Claim
130 words
A method of data expansion, characterized in that it comprises the steps of: receiving an incoming compressed encoded data stream and separating said incoming compressed data stream into units; identifying in said incoming compressed data stream a header portion comprising indications defining the identify of each user selected dictionary used in forming said compressed data stream and, accessing user selected compiled dictionaries of units having compressed code equivalents for each unit stored in association with the uncompressed unit and comparing said separated units from said incoming stream against said user selected compiled dictionaries; and outputting the decompressed code equivalents for said incoming units for which a true comparison is found in said comparing step and outputting said data stream for any said unit for which no true comparison is found.
Claim 10
Independent Claim
130 words
A method of data expansion, characterized in that it comprises the steps of: receiving an incoming compressed encoded data stream and separating said incoming compressed data stream into units; identifying in said incoming compressed data stream a header portion comprising indications defining the identify of each user selected dictionary used in forming said compressed data stream and, accessing user selected compiled dictionaries of units having compressed code equivalents for each unit stored in association with the uncompressed unit and comparing said separated units from said incoming stream against said user selected compiled dictionaries; and outputting the decompressed code equivalents for said incoming units for which a true comparison is found in said comparing step and outputting said data stream for any said unit for which no true comparison is found.
Claim 11
Dependent Claim
50 words
A method as described in Claim 7 characterized in that:: said unit entries in said user selected compiled dictionaries are arranged in order of merit established by multiplying the average frequency of occurrence of each said unit in the language in which it is used by its length in characters.
Claim 12
Dependent Claim
51 words
A method as described in Claim 7 or 8, characterized in that: at least one of said dictionaries comprises a control table of entries comprising segment identifiers for each segment of each said user selected dictionary used in compressing said data and identified in said header in said compressed data stream.
Claim 13
Independent Claim
38 words
A method as described in Claims anyone of claims 7 to 9 characterized in that: said dictionaries are assigned to byte addressable memory locations in a computer memory access system having memory addresses of integral whole number bytes.
Claim 14
Dependent Claim
261 words
A data compression and decompression system, comprising: a transmitter and a receiver and means for connecting said transmitter to said receiver for the transmission and reception of compressed data, said transmitter including means for accepting an incoming uncompressed encoded data stream and for separating said stream into units; said transmitter also comprising means for comparing said units against at least one user selected compiled dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed encoded units and further comprising; means for outputting a compressed data header comprising indications for defining the identity of each said user selected dictionary used in compressing said data; and means for outputting the compressed code equivalents for incoming units for which a true comparison is found in said comparing step and outputting the uncompressed encoded data stream for any said unit for which no true comparison is found; said receiver including means for receiving and analyzing said header for defining the identity of each of said user selected dictionaries used in compressing said compressed data stream ; means for separating said incoming compressed encoded data stream into units; means for comparing said units against at least one of said user selected and header identified compiled dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed encoded units; and means for outputting uncompressed equivalents for incoming units for which a true comparison is found in said comparing step and for outputting said data stream for any said unit for which no true comparison is found.
Claim 15
Dependent Claim
261 words
A data compression and decompression system, comprising: a transmitter and a receiver and means for connecting said transmitter to said receiver for the transmission and reception of compressed data, said transmitter including means for accepting an incoming uncompressed encoded data stream and for separating said stream into units; said transmitter also comprising means for comparing said units against at least one user selected compiled dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed encoded units and further comprising; means for outputting a compressed data header comprising indications for defining the identity of each said user selected dictionary used in compressing said data; and means for outputting the compressed code equivalents for incoming units for which a true comparison is found in said comparing step and outputting the uncompressed encoded data stream for any said unit for which no true comparison is found; said receiver including means for receiving and analyzing said header for defining the identity of each of said user selected dictionaries used in compressing said compressed data stream ; means for separating said incoming compressed encoded data stream into units; means for comparing said units against at least one of said user selected and header identified compiled dictionary of units having compressed code equivalents for each unit stored in association with the uncompressed encoded units; and means for outputting uncompressed equivalents for incoming units for which a true comparison is found in said comparing step and for outputting said data stream for any said unit for which no true comparison is found.
References Cited (Backward Citations)
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