Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 1 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 1 of 63
`
`EXHIBIT 2
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 2 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 2 of 63
`
`United States Patent
`(12)
`Farber et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,928,442 B2
`Aug. 9, 2005
`
`USOO692844232
`
`(54)
`
`ENFORCEMENT AND POLICING OF
`LICENSED CONTENT USING
`CONTENT-BASED IDENTIFIERS
`
`Inventors:
`
`(75)
`
`(73)
`
`Assignees:
`
`(*)
`
`Notice:
`
`David A. Farber, Ojai, CA (US);
`Ronald D. Lachman, Northbrook, IL
`(US)
`
`Kineteeh, Inc., Northbrook, IL (US);
`Savvis, Ine., Town & Country, MO
`(US)
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21)
`
`(32)
`
`(05)
`
`(63)
`
`(51)
`(53)
`
`(58)
`
`(56)
`
`Appl. N0.:
`Filed:
`
`09/987,723
`
`Nov. 15, 2001
`Prior Publication Data
`
`US 2002/0052884 A1 May 2. 2002
`
`Related U.S. Application Data
`
`1:.UI'IlinlIIIIon of npplimlinn No. 1.191283. 1le. him! on Apr. 1.
`|‘J‘19.nnwl’a1. No (1.415.28111 which is a dlvisiun OI
`npplienlion No. 11579011.,1179 IIILII on (31:1. 24. W97. new l’al.
`9111.5..978‘19I. which in a Lantinuation of application Nu.
`UHI425 1611 filed on Apr 11.1995 110“ abandoned.
`Int. Cl.7
`.G06F 17/30
`U..S Cl.
`707/10 707/3; 707/;101
`.
`707/700 709/203; 709/219; 709/229
`Field of Search.
`.707/3,6,9. 10,
`707/101, 200;709/203, 219 229
`References Cited
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`
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`3/1983
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`10/1983
`
`Evangelisti
`Mitchell
`Ciehelll
`Rivest
`Rivest
`Neches
`
`(Continued)
`
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`EI’
`
`0592045
`
`4/1994
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`
`(Continued)
`
`Primary Examiner—Luke S Wossum
`Assistant Examiner—Khanh Pham
`(74) Attorney, Agar/l, or Firm—Davidson Berquist Jackson
`& Gowdey, LLP
`
`(57)
`
`ABSTRACT
`
`Data files are distributed across a plurality ofcomputers. The
`computers may form a network such as a content delivery
`network (CDN) or a peer-to—peer network. The network may
`operate as a TCP/IP network such as the Internet. Data files
`may represent may represent digital messages,
`images,
`videos or audio signals. For content—data items or files in
`the system—a name is obtained (or determined), where the
`name is based, at least in part, on a given function ofthe data
`in a data item or file. The given function may be a message
`digest or hash function, and it may be MD4, MD5, and SI-IA.
`A cony of a requested file is only provided to licensed (or
`authorized) parties. The system may check one or more
`computers for unauthorized or unlicensed content. Content
`is sewed based on a measure of availability of servers.
`
`56 Claims, 31 Drawing Sheets
`
`GDMPU I E IIID FUNCHON ON
`DATA ITEM
`
`DATA ITEM
`
`.14
`APPEND LENGTH MODULO 32 OF
`
`I
`1
`
`EXHIBIT 2 - 1
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 3 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 3 of 63
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`Page 2
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`file System Integrity Checker", COAST Labs. Dept. of
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`Bert dem Beer 61 al., Collisions for the compression function
`of MDS, pp. 292—304.
`Sakti Pramanik et al., Multi—Directory Hasing, 1993, Info.
`Sys., vol. 18, No. 1, pp. 63—74.
`Murlidhar Koushik, Dynamic [lashing with Distributed
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`Performance, 1993, Info. Sys., vol. 18, No. 5, pp. 299—317.
`Witold Litwin et al., LH'—Linear Hashing for Distributed
`Files, HP Labs Tech. Report No. HPL—93—21, Jun. 1993, pp.
`1—22.
`
`Yuliang Zheng et al., l-lAVAI.—A One—Way Hashing Algo-
`rithm with Variable Length of Output (Extended Abstract),
`pp. 83—105.
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`versus Nonlinearity, Pieprzky, pp. 156—164.
`
`EXHIBIT 2 - 2
`
`.................. 707/1
`
`.............. 707/2
`
`707/2
`
`11/1983 Summer, Jr.
`4,414,624 A
`4/1984 Fletcher
`4,441,155 A
`8/1984 Benhase
`4,464,713 A
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`2/1986 Emry, Jr.
`4,571,700 A
`3/1986 Matick
`4,577,293 A
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`.................. 705/54
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`. 709/303
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`
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`
`.
`. 709/202
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`
`9/1998 Nguyen ........
`707/1
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`.................. 345/810
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`
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`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 4 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 4 of 63
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`US 6,928,442 132
`Page 3
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`Witold Litwin et a1., Linear Hashing for Distributed Files,
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`Support Pipelined Hash Joins, ACM SIGMOD, pp. 69—78,
`May 1993.
`Thomas A. Berson, Ditl'erential Cryptanalysis Mod 232 with
`Applications to MDS, pp. 69—81.
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`mance Evaluation, Twenty—Seventh Hawaii International
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`“Basic HTTP as defined in 1992", www.w3.org/Protocols/
`HTTPthml, 1992.
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`
`* cited by examiner
`
`EXHIBIT 2 - 3
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 5 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 5 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 1 0f 31
`
`US 6,928,442 B2
`
`106
`
`102
`
`PROCESSOR
`
`....———
`
`102
`
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`
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`
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`
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`
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`
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`
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`
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`
`PROCESSOR
`
`STORAGE
`
`DEVICE
`
`DEVICE
`
`STORAGE
`
`192
`
`EXHIBIT 2 - 4
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 6 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 6 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 2 of 31
`
`US 6,928,442 B2
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`EXHIBIT 2 - 5
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 7 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 7 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 3 0f 31
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`US 6,928,442 B2
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`EXHIBIT 2 - 6
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`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 8 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 8 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 4 0f 31
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`US 6,928,442 B2
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`EXHIBIT 2 - 7
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`FIG. 3
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`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 9 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 9 of 63
`
`US. Patent
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`Aug. 9, 2005
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`Sheet 5 0f 31
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`EXHIBIT 2 - 8
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`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 10 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 10 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 6 0f 31
`
`US 6,928,442 B2
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`FIG. 10(0)
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`
`APPEND LENGTH MODULO 32 OF
`
`EXHIBIT 2 - 9
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 11 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 11 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 7 of 31
`
`US 6,928,442 B2
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`
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`
`EXHIBIT 2 - 10
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 12 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 12 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 8 of 31
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`US 6,928,442 B2
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`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 13 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 13 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 9 0f 31
`
`US 6,928,442 B2
`
`FIG. l2
`
`
`
` $238
`$240
`
`FILE
`UPDATE
`
`
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`
`
`
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`LIST
`
`$242
`
`SEND MESSAGE TO
`
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`
` 8246
`MIRROR
`
`(IF DESIRED)
`
`
`
`CACHE SERVER T0
`
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`
`COMPRESS
`(IF DESIRED)
`
`
`
`
`EXHIBIT 2 - 12
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 14 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 14 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 10 0f 31
`
`US 6,928,442 B2
`
`FIG. I3
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`8250
`SEARCH FOR
`THE
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`ASSIMILATE
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`
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`
`8258
`
`FILE ID
`
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`
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`
`FREEZE
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`DIRECTORY
`
`EXHIBIT 2 - 13
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 15 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 15 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 11 0f 31
`
`US 6,928,442 B2
`
`
`
`8260
`
`CONFIRM THAT
`
`TRUE NAME
`
`EXISTS LOCALLY
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`8262
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`FIG.|4
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`LDE TABLE
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`
`CONFIRM THAT
`
`8264
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`EXISTS
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`NAMED FILE
`
`8268
`DELETE
`
`EXISTS?
`
`
`
`TRUE FILE
`
`8270
`
`
`
`CREATE
`
`ENTRY IN LDE
`
`
`& UPDATE
`
`
`EXHIBIT 2 — 14
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 16 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 16 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 12 0f 31
`
`US 6,928,442 B2
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`EXHIBIT 2 - 15
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`
`
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 17 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 17 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 13 of 31
`
`US 6,928,442 B2
`
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`EXHIBIT 2 - 16
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 18 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 18 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 14 0f 31
`
`US 6,928,442 B2
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`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 19 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 19 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 15 of 31
`
`US 6,928,442 B2
`
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`EXHIBIT 2 - 18
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 20 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 20 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 16 0f 31
`
`US 6,928,442 B2
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`EXHIBIT 2 - 19
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 21 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 21 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 17 0f 31
`
`US 6,928,442 B2
`
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`EXHIBIT 2 - 20
`
`
`
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 22 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 22 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 18 0f 31
`
`US 6,928,442 B2
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`EXHIBIT 2 - 21
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 23 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 23 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 19 0f 31
`
`US 6,928,442 B2
`
`
`
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`EXHIBIT 2 - 22
`
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 24 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 24 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 20 0f 31
`
`US 6,928,442 B2
`
`ovmw
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`EXHIBIT 2 - 23
`
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 25 of 63
`3
`Mmm
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`EXHIBIT 2 - 24
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 26 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 26 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 22 0f 31
`
`US 6,928,442 B2
`
`
`
` 8354
`WAIT FOR
`
`FREEZE LOCK
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`TRUE FILE
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`
`
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`
`
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`
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`REMOVE FILE ID
`AND COMPRESSED
`FILE ID
`
`
`
`EXHIBIT 2 - 25
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 27 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 27 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 23 of 31
`
`US 6,928,442 B2
`
`
`
`
`8365
`
`GET
`
`OPERATION
`
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`
`FIG. 22
`
`8388
`
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`
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`
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`
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`
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`
`8370
`8378
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`MODIFY USE
`NAME IN AUDIT
`
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`COUNT OF EACH
`FILE
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`
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`
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`
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`LAST ACCESS AND
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`
`
`
`EXHIBIT 2 - 26
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 28 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 28 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 24 of 31
`
`US 6,928,442 B2
`
`S382
`
`FIG. 23
`
`VERIFY
`GROOMING
`LOCK OFF
`
`COUNTS
`
`8386
`
`SET GROOM
`
`EXHIBIT 2 - 27
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 29 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 29 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 25 of 31
`
`US 6,928,442 B2
`
`SIZES
`
`S394
`
`ADJUST FILE
`
`EXHIBIT 2 - 28
`
`8392
`
`INCREMENT
`
`GROOMING
`
`DELETE COUNT
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 30 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 30 of 63
`
`US. Patent
`
`Aug. 9,2005
`
`Sheet 26 of 31
`
`Us 6,928,442 B2
`
`FIG. 25
`
`LOCK
`
`$398
`
`UNLOCK
`
`GROOMING
`
`EXHIBIT 2 - 29
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 31 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 31 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 27 0f 31
`
`US 6,928,442 B2
`
`GEN.oE
`
`.N>AJ<UOJ
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`EXHIBIT 2 - 30
`
`
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`
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`

`

`e8
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`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 32 of 63
`6
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`EXHIBIT 2 - 31
`
`
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`
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`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 33 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 33 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 29 0f 31
`
`US 6,928,442 B2
`
`
`
`29.5an>JZO-D<mm
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`EXHIBIT 2 - 32
`
`
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`
`

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`a
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`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 34 of 63
`1/40/01d
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`EXHIBIT 2 - 33
`
`
`
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 35 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 35 of 63
`
`US. Patent
`
`Aug. 9, 2005
`
`Sheet 31 0f 31
`
`US 6,928,442 B2
`
`mm.9“.
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`EXHIBIT 2 - 34
`
`
`
`
`

`

`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 36 of 63
`Case 5:18-cv-03462-BLF Document 31-2 Filed 10/04/18 Page 36 of 63
`
`US 6,928,442 B2
`
`1
`ENFORCEMENT AND POLICING 0F
`LICENSED CONTENT USING CONTENT-
`[IASED IDENTIFIERS
`
`This is a continuation of application Ser. No. 09/283,160,
`filed Apr. 1, 1999, now US. Pat. No. 6,415,280, which is a
`division of application Ser. No. flit?96tl,079, filed Oct. 24,
`1997, now U.S. Pat. No. 5,978,791 filed Oct. 24, 2001 which
`is a continuation ofSer. No. 08/425,160, filed Apr. 11, 1995,
`now abandoned.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This invention relates to data processing systems and,
`more particularly, to data processing systems wherein data
`items are identified by substantially unique identifiers which
`depend on all of the data in the data items and only on the
`data in the data items.
`
`2. Background of the Invention
`Data processing (DI’) systems, computers, networks of
`computers, or the like, typically offer users and programs
`various ways to identify the data in the systems.
`Users typically identify data in the data processing system
`by giving the data some form of name. For example, a
`typical operating system (US) on a computer provides a tile
`system in which data items are named by alphanumeric
`identifiers. Programs typically identify data in the data
`processing system using a location or addrem. For example,
`a program may identify a record in a tile or database by using
`a record number which serves to locate that record.
`in all but the most primitive operating systems, users and
`programs are able to create and use collections of named
`data items,
`these collections themselves being named by
`identifiers. These named collections can then, themselves,
`be made part of other named collections. For example, an
`()8 may provide mechanisms to group files (data items) into
`directories (collections). 'l‘heSe directories can then, them-
`selves be made part of other directories. A data item may
`thus be identified relative to these nested directories using a
`sequence of names, or a so-callcd pathnamc, which defines
`a path through the directories to a particular data item (file
`or directory).
`As another example. a database management system may
`group data records (data items} into tables and then group
`these tables into database tiles (collections). The complete
`address of any data record can then be specilied using the
`database file name, the table name, and the record number of
`that data record.
`
`Other examples of identifying data items include: identi-
`fying files in a network file system, identifying objects in an
`object-oriented database,
`identifying images in an image
`database, and identifying articles in a text database.
`In general, tlte terms “data" and “data item" as used herein
`refer to sequences of bits. Thus a data item may be the
`contents of a file, a portion of a file, a page in memory, an
`object
`in an object-oriented program, a digital message, a
`digital scanned image. a part of a video or audio signal, or
`any other entity which can be represented by a sequence of
`bits. The term "data processing” herein refers to the pro-
`cessing ot’ data items, and is sometimes dependent on the
`type of data item being processed. For example, a data
`processor for a digital
`image may dill‘er from a data pro-
`cessor for an audio signal.
`In all of the prior data processing systems the names or
`identifiers provided to identify data items (the data items
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`being tiles, directories, records in the database, objects in
`object-oriented programming, locations in memory or on a
`physical device, or the like) are always defined relative to a
`specific context. For instance,
`the tile identified by a par-
`ticular file name can only be determined when the directory
`containing the file (the context) is known. The file identified
`by a pathname can be determined only when the file system
`(context) is known. Similarly,
`the addresses in a process
`address space, the keys in a database table, or domain names
`on a global computer network such as the Internet are
`meaningful only because they are specified relative to a
`context.
`
`In prior art systems for identifying data items there is no
`direct relationship between the data names and the data item.
`The same data name in two different contexts may refer to
`different data items, and two different data names in the
`same context may refer to the same data item.
`In addition, because there is no correlation between a data
`name and the data it refers to, thereis no a priori way to
`confirm that a given data item is in fact the one named by a
`data name. For instance, in a DP system, if one processor
`requests that another processor deliver a data item with a
`given data name,
`the requesting processor cannot,
`in
`general. Verify that
`the data delivered is the correct data
`(given only the name).
`'l'hercfore it may require further
`processing. typically on the part of the requester, to verify
`that the data item it has obtained is.
`in fact. the item it
`requested.
`A common operation in a DP system is adding a new data
`item to the system. When a new data item is added to the
`system, a name can be assigned to it only by updating the
`context
`in which names are defined. Thus such systems
`require a centralized mechanism for the management of
`names. Such a mechanism is required even in a multi-
`processing system xvhcn data items are created and identified
`at separate processors in distinct
`locations. and in which
`there is no other need for communication when data items
`are added.
`
`In many data processing systems or environments, data
`items are transferred between different
`locations in the
`system.
`'l'hese locations may be processors it!
`the data
`processing system, storage devices. memory. or the like. For
`example. one processor may obtain a data item from another
`processor or from an external storage device, such as a
`lloppy disk, and may incorporate that data item into its
`system (using the name provided with that data item}.
`However, when a processor (or some location) obtains a
`data item from another location in the DP system,
`it
`is
`possible that this obtained data item is already present in the
`system (either at the location of the processor or at some
`other location accessible by the processor) and therefore a
`duplicate of the data item is created. This situation is
`common in a network data processing environment where
`proprietary software products are installed from floppy disks
`onto several processors sharing a common file server. In
`these systems. it is often the case that the same product will
`he installed on several systems, so that several copies 01.
`each file will reside on the common file server.
`In some data processing systems in which several pro-
`cessors are connected in a network, one system is designated
`as a cache server to maintain master copies of data items,
`and other systems are designated as cache cliean to copy
`local copies of the master data items into a local cache on an
`as-needed basis. Before using a cached item, a cache client
`must either reload the cached item, be infortned of changes
`to the cached item, or confirm that the master item corre-
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`sponding to the cached item has not changed. In otherwnrds,
`a cache client must synchronize its data items with those on
`the cache server. This synchronization may involve reload-
`ing data items onto the cache client. The need to keep the
`cache synchronized or reload it adds significant overhead to
`existing caching mechanisms.
`In view of the above and other problems with prior art
`systems. it is therefore desirable to have a mechanism which
`allows each processor in a multiprocessor system to deter~
`mine a common and substantially unique identifier for a data
`item, using only the data in the data item and not relying on
`any sort of context.
`It is further desirable to have a mechanism for reducing
`multiple copies ofdata items in a data processing system and
`to have a mechanism which enables the id