KWWSZZZZRUJ75127(GUS
`
`7KH +773 'LVWULEXWLRQ DQG 5HSOLFDWLRQ
`3URWRFRO
`
`127('53
`
`6XEPLWWHG WR :& $XJXVW  
`
`7KH ODWHVW YHUVLRQ RI WKLV GRFXPHQW
`KWWSZZZZRUJ75127(GUS
`7KLV YHUVLRQ RI WKLV GRFXPHQW
`KWWSZZZZRUJ75127(GUS
`(GLWRUV
`$UWKXU YDQ +RII 0DULPED ,QF
`-RKQ *LDQQDQGUHD 1HWVFDSH ,QF
`0DUN +DSQHU 6XQ 0LFURV\VWHPV ,QF
`6WHYH &DUWHU 1RYHOO ,QF
`0LOR 0HGLQ $W +RPH &RUS
`
`6WDWXV RI WKLV 'RFXPHQW
`
`7KLV GRFXPHQW LV D 127( PDGH DYDLODEOH E\ WKH : &RQVRUWLXP IRU GLVFXVVLRQ RQO\ 7KLV LQGLFDWHV QR
`HQGRUVHPHQW RI LWV FRQWHQW QRU WKDW WKH &RQVRUWLXP KDV LV RU ZLOO EH DOORFDWLQJ DQ\ UHVRXUFHV WR WKH
`LVVXHV DGGUHVVHG E\ WKH 127(
`
`7KLV GRFXPHQW LV D VXEPLVVLRQ WR :& IURP 0DULPED 1HWVFDSH 6XQ 0LFURV\VWHPV 1RYHOO DQG
`#+RPH 3OHDVH VHH $FNQRZOHGJHG 6XEPLVVLRQV WR :& UHJDUGLQJ LWV GLVSRVLWLRQ
`
`$EVWUDFW
`
`7KLV GRFXPHQW SURYLGHV D VSHFLILFDWLRQ RI D SURWRFRO IRU WKH HIILFLHQW UHSOLFDWLRQ RI GDWD RYHU +773
`
`7DEOH RI &RQWHQWV
`
` ,QWURGXFWLRQ
`
` 7KH +773 'LVWULEXWLRQ DQG 5HSOLFDWLRQ 3URWRFRO
`
` &RQWHQW ,GHQWLILHUV
`
` ,QGH[ )RUPDW
`
` ,QGH[ 5HWULHYDO
`
` &RQWHQW %DVHG $GGUHVVLQJ
`
` 'LIIHUHQWLDO 'RZQORDGV
`
` +773 3UR[\ &DFKLQJ
`
`3DJH  RI 
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`

`KWWSZZZZRUJ75127(GUS
`
` %DFNZDUG &RPSDWLELOLW\
`
` &RQFOXVLRQ
`
` 5HIHUHQFHV
`
`$SSHQGLFHV
`
`$ ,QGH[ '7'
`
` ,QWURGXFWLRQ
`
`7KLV GRFXPHQW SURYLGHV D FRPSOHWH GHVFULSWLRQ RI WKH +773 'LVWULEXWLRQ DQG 5HSOLFDWLRQ 3URWRFRO
`'53

 7KH JRDO RI WKH '53 SURWRFRO LV WR VLJQLILFDQWO\ LPSURYH WKH HIILFLHQF\ DQG UHOLDELOLW\ RI GDWD
`GLVWULEXWLRQ RYHU +773 +HUH LV D PRUH GHWDLOHG OLVW RI JRDOV
`
`z 3URYLGH D ZLGHO\ DSSOLFDEOH PHFKDQLVP IRU WKH HIILFLHQW UHSOLFDWLRQ RI GDWD DQG FRQWHQW
`z ,PSURYH WKH HIILFLHQF\ DQG UHOLDELOLW\ RI FDFKLQJ VHUYHUV DQG SUR[LHV
`z 6LJQLILFDQWO\ LPSURYH WKH HIILFLHQF\ RI VXEVFULSWLRQEDVHG GDWD DQG FRQWHQW GLVWULEXWLRQ
`z ,PSURYHG UHOLDELOLW\ DQG YHUVLRQLQJ IRU WKH GLVWULEXWLRQ RI PLVVLRQFULWLFDO DSSOLFDWLRQV DQG GDWD
`z &UHDWH DQ LQWHURSHUDELOLW\ VWDQGDUG IRU UHSOLFDWLQJ FRQWHQW EHWZHHQ FOLHQWV DQG VHUYHUV IURP
`GLIIHUHQW YHQGRUV
`z .HHS WKH SURWRFRO VLPSOH WR DYRLG LQFRPSDWLELOLWLHV
`z 3URYLGH IXQFWLRQDOLW\ WKDW LV FRPSOHPHQWDU\ WR H[LVWLQJ VWDQGDUGV
`z 3URYLGH IXQFWLRQDOLW\ WKDW LV EDFNZDUG FRPSDWLEOH ZLWK H[LVWLQJ +773 VHUYHUV DQG SUR[LHV
`z 3URYLGH IXQFWLRQDOLW\ WKDW FDQ EH GHSOR\HG DQ\ZKHUH ZKHUH +773 LV DYDLODEOH WRGD\
`
`7KH +773 'LVWULEXWLRQ DQG 5HSOLFDWLRQ 3URWRFRO ZDV GHVLJQHG WR HIILFLHQWO\ UHSOLFDWH D KLHUDUFKLFDO VHW
`RI ILOHV WR D ODUJH QXPEHU RI FOLHQWV 1R DVVXPSWLRQ LV PDGH DERXW WKH FRQWHQW RU W\SH RI WKH ILOHV WKH\
`DUH VLPSO\ ILOHV LQ VRPH KLHUDUFKLFDO RUJDQL]DWLRQ
`
`$IWHU WKH LQLWLDO GRZQORDG D FOLHQW FDQ NHHS WKH GDWD XSWRGDWH XVLQJ WKH '53 SURWRFRO 8VLQJ '53 WKH
`FOLHQW FDQ GRZQORDG RQO\ WKH GDWD WKDW KDV FKDQJHG VLQFH WKH ODVW WLPH LW FKHFNHG 'RZQORDGLQJ RQO\
`WKH GLIIHUHQFHV LV PXFK PRUH HIILFLHQW EHFDXVH GDWD W\SLFDOO\ HYROYHV VORZO\ RYHU WLPH DQG EHFDXVH
`FKDQJHV DUH XVXDOO\ UHVWULFWHG WR RQO\ D VXEVHW RI WKH GDWD 2QH RI WKH JRDOV RI WKH '53 SURWRFRO LV WR
`DYRLG GRZQORDGLQJ WKH VDPH GDWD PRUH WKDQ RQFH
`
`7KH GDWD WKDW LV GLVWULEXWHG FDQ FRQVLVW RI PRUH WKDQ MXVW +70/ SDJHV LW FDQ FRQVLVW RI DQ\ NLQG RI
`FRGH RU FRQWHQW 7KH '53 SURWRFRO SURYLGHV VWURQJ JXDUDQWHHV DERXW GDWD YHUVLRQLQJ 7KLV LV D
`UHTXLUHPHQW IRU GLVWULEXWLQJ PLVVLRQ FULWLFDO DSSOLFDWLRQV EHFDXVH JHWWLQJ WKH FRUUHFW YHUVLRQ RI HDFK
`FRPSRQHQW LV D QHFHVVDU\ WR HQVXUH D FRPSOHWH DSSOLFDWLRQ ZLOO ZRUN FRUUHFWO\ &RUUHFW ILOH YHUVLRQLQJ
`XVLQJ H[LVWLQJ +773 UHTXHVWV LV SUREOHPDWLF EHFDXVH WKHUH LV FXUUHQWO\ QR UHOLDEOH PHFKDQLVP IRU
`LGHQWLI\LQJ D SDUWLFXODU YHUVLRQ RI D ILOH
`
`7KH '53 SURWRFRO XVHV FRQWHQW LGHQWLILHUV WR DXWRPDWLFDOO\ VKDUH UHVRXUFHV WKDW DUH UHTXHVWHG PRUH
`WKDQ RQFH 7KLV HOLPLQDWHV UHGXQGDQW WUDQVIHUV RI FRPPRQO\ XVHG UHVRXUFHV 7KH FRQWHQW LGHQWLILHUV
`XVHG LQ WKH '53 SURWRFRO DUH EDVHG RQ ZLGHO\ DFFHSWHG FKHFNVXP WHFKQRORJ\
`
`7KH '53 SURWRFRO XVHV D GDWD VWUXFWXUH FDOOHG DQ LQGH[ ZKLFK LV FXUUHQWO\ VSHFLILHG XVLQJ WKH
`H;WHQVLEOH 0DUNXS /DQJXDJH ;0/

 %HFDXVH WKH LQGH[ GHVFULEHV PHWD GDWD ZH DQWLFLSDWH XVLQJ WKH
`5HVRXUFH 'HVFULSWLRQ )UDPHZRUN 5')

 LQ D IXWXUH YHUVLRQ RI WKH '53 SURWRFRO VSHFLILFDWLRQ ;0/
`LV XVHG LQ WKH LQWHULP EHFDXVH WKH 5') VWDQGDUG ZDV QRW ILQDOL]HG DW WKH WLPH RI ZULWLQJ
`
`7KH '53 SURWRFRO UHOLHV RQ H[LVWLQJ +773 IXQFWLRQDOLW\ WR DFKLHYH EHWWHU SHUIRUPDQFH ZKHQ
`
`3DJH  RI 
`
`
`
`
`
`
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`%
`
`!
`
`(
`
`0
`
`1
`
`
`%
`'
`
`*
`1
`*
`
`4
`
`&
`
`!
`
`+
`+
`2
`
`/
`
`!
`
`*
`
`'
`
`,
`.
`
`-
`!
`
`/
`
`"
`
`'
`
`)
`
`3
`
`,
`
`!
`
`/
`
`"
`
`!
`
`)
`
`#
`
`*
`
`$
`(
`
`)
`
`#
`
`)
`
`"
`
`(
`
`!
`)
`
`+
`
`

`

`5
`
`6
`
`7
`
`8
`
`9
`
`:
`
`6
`
`;
`
`KWWSZZZZRUJ75127(GUS
`
`UHSOLFDWLQJ ILOHV DQG LW LV EDFNZDUG FRPSDWLEOH ZLWK H[LVWLQJ +773 DQG +773 SUR[LHV VR WKDW LW
`FDQ EH GHSOR\HG LPPHGLDWHO\ 7R IXUWKHU LPSURYH WKH GRZQORDG HIILFLHQF\ DQG FDFKLQJ EHKDYLRU RI
`+773 WKH SURSRVDO LQWURGXFHV QHZ +773 KHDGHU LQIRUPDWLRQ WKDW PD\ EHFRPH SDUW RI WKH FRUH +773
`SURWRFRO VSHFLILFDWLRQ LQ WKH IXWXUH %HFDXVH WKH '53 SURWRFRO LV OD\HUHG RQ +773 LW ZLOO EHQHILW IURP
`RQJRLQJ HIIRUWV LQ WKH +7731* ZRUNLQJ JURXS
`
`7KH '53 SURWRFRO LV EDVHG RQ WHFKQRORJ\ ZKLFK ZDV RULJLQDOO\ GHYHORSHG LPSOHPHQWHG DQG GHSOR\HG
`E\ 0DULPED ,QF $OWKRXJK LW ZDV RULJLQDOO\ GHVLJQHG IRU VRIWZDUH GLVWULEXWLRQ LW LV ZLGHO\ DSSOLFDEOH
`LQ PDQ\ GLIIHUHQW DUHDV DQG LW HQDEOHV WKH ODUJH VFDOH DXWRPDWLF GLVWULEXWLRQ RI VRIWZDUH GDWD DQG
`FRQWHQW WR PDQ\ GLIIHUHQW FOLHQWV
`
` 7KH +773 'LVWULEXWLRQ DQG 5HSOLFDWLRQ 3URWRFRO
`
` &RQWHQW ,GHQWLILHUV
`
`7KH '53 SURWRFRO XVHV FRQWHQW LGHQWLILHUV WR LGHQWLI\ LQGLYLGXDO SLHFHV RI FRQWHQW $ FRQWHQW LGHQWLILHU
`LV D WRNHQ WKDW FDQ EH XVHG WR XQLTXHO\ LGHQWLI\ DQ\ SLHFH RI GDWD RU FRQWHQW ,W FDQ DOVR EH XVHG WR
`GHWHUPLQH ZKHWKHU WZR SLHFHV RI FRQWHQW DUH LGHQWLFDO ZLWK JUHDW DFFXUDF\
`
`$ FRQWHQW LGHQWLILHU FRQVLVWV RI RQH RU PRUH 8QLIRUP 5HVRXUFH ,GHQWLILHUV 85,

VHSDUDWHG E\ FRPPDV
`7KH 85,V DUH FRPELQHG WRJHWKHU LQWR D VLQJOH FRQWHQW LGHQWLILHU DQG IRUP D JOREDOO\ XQLTXH LGHQWLILHU
`+HUH LV WKH V\QWD[ RI D FRQWHQWLGHQWLILHU
`
` FRQWHQWLGHQWLILHU 85,   85,

`
`7\SLFDOO\ D FKHFNVXP DOJRULWKP LV XVHG WR JHQHUDWH D FRQWHQW LGHQWLILHU IRU D SLHFH RI FRQWHQW 2QH RI
`WKH FKHFNVXP DOJRULWKPV ZKLFK FDQ EH XVHG LV WKH 0HVVDJH 'LJHVW DOJRULWKP IURP 56$ 7KH 0'
`DOJRULWKP LV D ZHOONQRZQ DOJRULWKP IRU FRPSXWLQJ D ELW FKHFNVXP IRU DQ\ ILOH RU REMHFW 6HH
`KWWSZZZUVDFRPSXEUIFW[W IRU GHWDLOV RQ WKH LPSOHPHQWDWLRQ RI WKH 0' DOJRULWKP
`
`7KH OLNHOLKRRG RI WZR GLIIHUHQW ILOHV SURGXFLQJ WKH VDPH 0' FKHFNVXP LV YHU\ VPDOO DERXW  LQ
`A

 DQG DV VXFK WKH 0' FKHFNVXP RI D ILOH FDQ EH XVHG WR FRQVWUXFW D UHOLDEOH FRQWHQW LGHQWLILHU
`WKDW LV YHU\ OLNHO\ WR XQLTXHO\ LGHQWLI\ WKH ILOH 7KH UHYHUVH LV DOVR WUXH ,I WZR ILOHV KDYH WKH VDPH 0'
`FKHFNVXP LW LV YHU\ OLNHO\ WKDW WKH ILOHV DUH LGHQWLFDO
`
`,W LV SRVVLEOH WR GHILQH D 8QLYHUVDO 5HVRXUFH 1DPH 851

 ZKLFK LV D NLQG RI 85, IRU D ELW 0'
`FKHFNVXP
`
` 0'851 XUQPG EDVHQXPEHU
`
`$QRWKHU FKHFNVXP DOJRULWKP XVHG LQ WKH '53 SURWRFRO LV WKH 6+$ DOJRULWKP IURP WKH 1DWLRQDO
`,QVWLWXWH RI 6WDQGDUGV DQG 7HFKQRORJ\ ,W LV VLPLODU WR WKH 0' DOJRULWKP EXW LWV FKHFNVXPV DUH 
`ELWV ORQJ DQG KDYH GLIIHUHQW SURSHUWLHV 6HH KWWSFVUFQLVWJRYILSVILSW[W IRU GHWDLOV RQ WKH
`LPSOHPHQWDWLRQ RI WKH 6+$ DOJRULWKP
`
`+HUH LV KRZ D 851 LV FUHDWHG XVLQJ D ELW 6+$ FKHFNVXP
`
`3DJH  RI 
`
`
`
`
`
`
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`

`KWWSZZZZRUJ75127(GUS
`
` 6+$851 XUQVKD EDVHQXPEHU
`
`%RWK 0' DQG 6+$ EDVHG 85,V XVH EDVH HQFRGLQJ WR HQFRGH WKH FKHFNVXP RI WKH FRQWHQW 7KH
`EDVH DOJRULWKP HQFRGHV HDFK  E\WHV RI WKH FKHFNVXP LQ  FKDUDFWHUV FRQWDLQLQJ  ELWV RI
`LQIRUPDWLRQ HDFK 7KH GHWDLOV RI WKH EDVH HQFRGLQJ DOJRULWKP DUH SDUW RI WKH 0,0( VSHFLILFDWLRQ
`
`1RWH WKDW D EDVH QXPEHU FDQ LQFOXGH
`
` DQG
`
` FKDUDFWHUV $OWKRXJK WKHVH FKDUDFWHUV DUH WUHDWHG
`VSHFLDOO\ LQ WKH 851 V\QWD[ VSHFLILFDWLRQ LW LV QRW QHFHVVDU\ WR HVFDSH WKHP ZKHQ XVHG LQ D FKHFNVXP
`851
`
`,I D FRQWHQW LGHQWLILHU FRQWDLQV D 85, WKDW UHIHUV WR D ZHOO NQRZQ FKHFNVXP DOJRULWKP VXFK DV 0' RU
`6+$ LW LV SRVVLEOH WR YHULI\ WKH LQWHJULW\ RI WKH FRQWHQW ,I QRQH RI WKH 85,V LQ WKH FRQWHQW LGHQWLILHU
`UHIHU WR D NQRZQ FKHFNVXP DOJRULWKP WKH FRQWHQW LGHQWLILHU VKRXOG EH WUHDWHG DV DQ RSDTXH VWULQJ WKDW
`FDQ EH XVHG IRU DGGUHVVLQJ SXUSRVHV RQO\
`
`+HUH DUH VRPH H[DPSOHV RI YDOLG FRQWHQW LGHQWLILHUV
`
` XUQPG)1*F0-/G'(<UFR*ES4
`
` XUQPG+8;=/4/0X,.=.'F-3F2$
`
` XUQVKDWKY'\YKI,TOY)H$0<J[$IPT
`
` KWWSZZZDFPHFRPLPDJHVIRRJLIXUQPG)1*F0-/G'(<UFR*ES4
`
` KWWSZZZDFPHFRP([DPSOHXUQ[YHUVLRQ
`
` IWSZZZDFPHFRP+HOOR:RUOG
`
`,Q DSSOLFDWLRQV ZKHUH WKH SRVVLELOLW\ RI GXSOLFDWHV IRU D JLYHQ 851 LV XQDFFHSWDEOH FRQWHQW LGHQWLILHUV
`FDQ EH JHQHUDWHG ZLWK WKH UHTXLUHG XQLTXHQHVV E\ XVLQJ PXOWLSOH DSSURSULDWH 85,V ,I IRU H[DPSOH
`YHUVLRQ QXPEHUV DUH XVHG LW LV LPSRUWDQW WR IXUWKHU TXDOLI\ WKH FRQWHQW LGHQWLILHU LQ RUGHU WR PDNH LW
`JOREDOO\ XQLTXH 7KLV FDQ EH DFKLHYHG E\ LQFOXGLQJ WKH 85/ RI WKH REMHFW WR ZKLFK WKH YHUVLRQ QXPEHU
`DSSOLHV LQ WKH FRQWHQW LGHQWLILHU
`
`$ FRQWHQW LGHQWLILHU LV RIWHQ HPEHGGHG LQ DQ +773 KHDGHU DQG WKHUHIRUH WKH 85,V LQ WKH FRQWHQW
`LGHQWLILHU DUH QRW DOORZHG WR FRQWDLQ UHVHUYHG FKDUDFWHUV VXFK DV VSDFHV RU FRPPD FKDUDFWHUV $OO
`UHVHUYHG FKDUDFWHUV VKRXOG EH HQFRGHG DV VSHFLILHG LQ WKH 85, VSHFLILFDWLRQ
`
` ,QGH[ )RUPDW
`
`7R GHVFULEH WKH H[DFW VWDWH RI D VHW RI GDWD ILOHV WKH '53 SURWRFRO XVHV D GDWDVWUXFWXUH FDOOHG DQ LQGH[
`$Q LQGH[ QRW RQO\ GHVFULEHV WKH KLHUDUFKLFDO VWUXFWXUH RI WKH ILOHV EXW LW DOVR GHVFULEHV WKH YHUVLRQ VL]H
`DQG W\SH RI HDFK ILOH $Q LQGH[ LV D VQDSVKRW RI WKH VWDWH RI D VHW RI ILOHV DW D SDUWLFXODU PRPHQW LQ WLPH
`
`$Q LQGH[ LV W\SLFDOO\ VWRUHG LQ PHPRU\ DV D WUHH GDWD VWUXFWXUH EXW LQ RUGHU IRU FOLHQWV DQG VHUYHUV WR
`FRPPXQLFDWH WKLV LQIRUPDWLRQ RYHU +773 DQ LQGH[ FDQ EH GHVFULEHG XVLQJ ;0/ 7KH LQGH[ '7'
`XVHG E\ WKH '53 SURWRFRO LV VSHFLILHG LQ $SSHQGL[ $ 8VLQJ WKLV '7' KHUH LV DQ H[DPSOH RI DQ LQGH[
`WKDW GHVFULEHV D KLHUDUFKLFDO VHW RI ILOHV
`
`3DJH  RI 
`
`
`
`
`
`
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`

`KWWSZZZZRUJ75127(GUS
`
` ";0/ 9(56,21  50' 121("!
`
` LQGH[!
`
` ILOH SDWK KRPHKWPO VL]H  LG XUQPG3()M:%'YVGDO6%<X;Z !
`
` ILOH SDWK OD\HUMV VL]H  LG XUQPG:<&XWR-W=V'V+,=PSJ !
`
` GLU SDWK LPDJHV!
`
` ILOH SDWK DFPHJLI VL]H  LG XUQPGKE=1;I84$-%5)O.64 !
`
` ILOH SDWK EDQQHUJLI VL]H  LG XUQPGWU;R1UNTYVL\'66MMJ !
`
` GLU!
`
` GLU SDWK MDYDFODVVHV!
`
` ILOH SDWK 6FUROOMDYD VL]H  LG XUQPG[M%NJ:RX6S)780,N[=J !
`
` ILOH SDWK JXLMDU VL]H  LG XUQPGWF8]Z'.XW6L7SPS$VLJ !
`
` GLU!
`
` LQGH[!
`
` ,QGH[ 5HWULHYDO
`
`$ '53 LQGH[ LV UHWULHYHG JLYHQ D 85/ WR WKH LQGH[ 7KH LQGH[ FDQ EH VWRUHG LQ DQ\ ILOH DQG FDQ EH
`UHWULHYHG XVLQJ D QRUPDO +773 *(7 UHTXHVW 7KH PLPH W\SH RI WKH LQGH[ ILOH DOORZV FOLHQWV WR WUHDW WKH
`LQGH[ DV D VSHFLDO ILOH ZKLFK SURYLGHV PHWD LQIRUPDWLRQ DERXW RWKHU ILOHV 7KH FOLHQW FDQ XVH WKH LQGH[
`WR DXWRPDWLFDOO\ GRZQORDG WKH ILOHV WKDW DUH VSHFLILHG
`
`7KH LQGH[ ILOH FDQ EH DQ RUGLQDU\ ILOH RQ DQ +773 VHUYHU EXW LW FDQ DOVR EH JHQHUDWHG G\QDPLFDOO\
`1RWH WKDW WKH LQGH[ LVQ
`W QHFHVVDULO\ JHQHUDWHG IURP D ILOH V\VWHP LW FRXOG DOVR UHSUHVHQW KLHUDUFKLFDO
`GDWD IURP D GLIIHUHQW VRXUFH VXFK DV D GDWDEDVH
`
`2QFH WKH LQLWLDO GRZQORDG LV FRPSOHWH D FOLHQW FDQ XSGDWH WKH FRQWHQW E\ GRZQORDGLQJ D QHZ YHUVLRQ
`RI WKH LQGH[ DQG FRPSDULQJ LW DJDLQVW WKH SUHYLRXV YHUVLRQ RI WKH LQGH[ %HFDXVH HDFK ILOH HQWU\ LQ WKH
`LQGH[ KDV D FRQWHQW LGHQWLILHU WKH FOLHQW FDQ GHWHUPLQH ZKLFK ILOHV KDYH FKDQJHG DQG VR GHWHUPLQH WKH
`PLQLPDO VHW RI ILOHV WKDW QHHG WR EH GRZQORDGHG LQ RUGHU WR EULQJ WKH FOLHQW XSWRGDWH
`
`,QGH[ %DVH 85/
`
`7KH LQGH[ ILOH LV W\SLFDOO\ ORFDWHG LQ WKH URRW GLUHFWRU\ RI WKH ILOH KLHUDUFK\ LW GHVFULEHV ,Q WKDW FDVH WKH
`EDVH 85/ RI WKH ILOHV LQ WKH LQGH[ LV WKH VDPH DV WKH EDVH 85/ RI WKH LQGH[ LWVHOI 7KH LQGH[ ILOH VKRXOG
`QRW EH OLVWHG LQ WKH LQGH[ LWVHOI
`
`$Q LQGH[ FDQ DOVR H[SOLFLWO\ VSHFLI\ D GLIIHUHQW DEVROXWH RU UHODWLYH EDVH 85/ XVLQJ WKH EDVH DWWULEXWH
`RI WKH LQGH[ WDJ 7KLV DOORZV DQ LQGH[ WR GHVFULEH ILOHV WKDW DUH ORFDWHG LQ D GLIIHUHQW GLUHFWRU\ RU HYHQ
`RQ D GLIIHUHQW VHUYHU
`
`)RU H[DPSOH LI WKH LQGH[ LV ORDGHG IURP WKH IROORZLQJ 85/
`
`
`%
`'
`
`*
`1
`*
`
`!
`
`!
`
`+
`+
`2
`
`/
`
`&
`
`'
`
`"
`
`-
`!
`
`/
`
`,
`.
`
`)
`
`3
`
`!
`
`!
`
`/
`
`"
`
`!
`)
`
`(
`
`0
`
`%
`
`!
`
`$
`(
`
`)
`
`#
`
`)
`
`"
`
`(
`
`1
`
`3DJH  RI 
`
`!
`
`)
`
`)
`*
`
`>
`
`/
`
`%
`
`/
`
`4
`
`1
`!
`*
`
`=
`
`!
`
`#
`2
`
`/
`
`5
`
`6
`
`7
`
`/
`
`0
`
`<
`
`!
`!
`
`"
`
`9
`
`3
`
`8
`
`%
`
`1
`
`)
`)
`
`/
`
`;
`
`(
`"
`
`:
`
`6
`
`
`
`
`
`
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`

`http://www.w3.org/TR/NOTE-drp-19970825
`KWWSZZZZRUJ75127(GUS
`
`
`http://www.acme.com/Examples/index.xml
` KWWSZZZDFPHFRP([DPSOHVLQGH[[PO
`
`8QOHVV D GLIIHUHQW EDVH 85/ LV VSHFLILHG LQ WKH LQGH[ WDJ WKH EDVH 85/ RI WKH LQGH[ ZLOO EH
`Unless a different base URL is specified in the index tag, the base URL of the index will be:
`
`
`http://www.acme.com/Examples/
` KWWSZZZDFPHFRP([DPSOHV
`
`7KDW PHDQV WKDW WKH LQGH[ LQ WKH H[DPSOH DERYH GHVFULEHV WKH IROORZLQJ ILOHV
`That means that the index in the example above describes the following files:
`
`3xamples/home.html
` KWWSZZZDFPHFRP([DPSOHVKRPHKWPO
`
`3xamples/layerl.js
` KWWSZZZDFPHFRP([DPSOHVOD\HUMV
`
`3xamples/images/acme.gif
` KWWSZZZDFPHFRP([DPSOHVLPDJHVDFPHJLI
`
`Examples/images/banner.gif
` KWWSZZZDFPHFRP([DPSOHVLPDJHVEDQQHUJLI
`
`Examples/java/classes/Scroll.java
` KWWSZZZDFPHFRP([DPSOHVMDYDFODVVHV6FUROOMDYD
`
` KWWSZZZDFPHFRP([DPSOHVMDYDFODVVHVJXLMDU
`
`Index Expiration
`,QGH[ ([SLUDWLRQ
`
`,Q WKH DEVHQFH RI DQ\ PHWD GDWD WKH FOLHQW VKRXOG REVHUYH WKH ([SLUHV ILHOG LQ WKH +773 UHSO\ RI WKH
`In the absence of any meta data, the client should observe the Expires field in the HTTP reply of the
`LQGH[ UHTXHVW WR GHWHUPLQH KRZ ORQJ WKH LQGH[ LV YDOLG :KHQ WKH LQGH[ H[SLUHV D QHZ YHUVLRQ RI WKH
`index request to determine how long the index is valid. When the index expires, a new version of the
`index should be downloaded.
`LQGH[ VKRXOG EH GRZQORDGHG
`
`7KLV SURYLGHV D VLPSOH PHFKDQLVP IRU VFKHGXOLQJ XSGDWHV RI LQGH[HV ,Q VRPH FDVHV DGGLWLRQDO PHWD
`This provides a simple mechanism for scheduling updates of indexes. In some cases additional meta
`GDWD ZLOO EH DYDLODEOH ZKLFK FDQ SURYLGH PRUH GHWDLOHG LQIRUPDWLRQ IRU VFKHGXOLQJ XSGDWHV RI WKH LQGH[
`data will be available which can provide more detailed information for scheduling updates of the index
`and the content it describes.
`DQG WKH FRQWHQW LW GHVFULEHV
`
`Index Caching
`,QGH[ &DFKLQJ
`
`$Q +773 SUR[\ PD\ FDFKH LQGH[HV LI WKH +773 KHDGHU LQGLFDWHV WKDW WKLV LV DOORZHG $Q +773 SUR[\
`An HTTP proxy may cache indexes if the HTTP header indicates that this is allowed. An HTTP proxy
`VKRXOG WUHDW LQGH[HV MXVW OLNH QRUPDO ILOHV 7KH +773 DQG +773 VSHFLILFDWLRQ SURYLGH D YDULHW\
`should treat indexes just like normal files. The HTTP/1.0 and HTTP/ 1.1 specification provide a variety
`RI FDFKH FRQWURO PHFKDQLVPV WKDW FDQ EH XVHG WR FRQWURO WKH FDFKLQJ RI LQGH[HV
`of cache control mechanisms that can be used to control the caching of indexes.
`
`$ VHUYHU ZKLFK JHQHUDWHV SHUVRQDOL]HG LQGH[HV WKDW DOO KDYH WKH VDPH EDVH 85/ ZLOO KDYH WR PDUN WKH
`A server which generates personalized indexes that all have the same base URL will have to mark the
`LQGH[ DV QRW FDFKHDEOH XVLQJ WKH VWDQGDUG +773 PHFKDQLVPV DV GHILQHG LQ +773 DQG +773
`index as not cacheable using the standard HTTP mechanisms as defined in HTTP/ 1.0 and HTTP/1.1
`SURWRFRO VSHFLILFDWLRQV
`protocol specifications.
`
` &RQWHQW %DVHG $GGUHVVLQJ
`2.4 Content Based Addressing
`
`
`OO\]O\UI-l>U-)l\)>—*
`
` Examples/java/classes/gui.jar
`
`
`
`
`files need to be downloaded, as well as the total size of the download.
`Because the client can determine the exact set of files that need to be downloaded, it is ossible to
`
`
`
`%HFDXVH WKH FOLHQW FDQ GHWHUPLQH WKH H[DFW VHW RI ILOHV WKDW QHHG WR EH GRZQORDGHG LW LV SRVVLEOH WR
`issue multi-file get requests to get all the files at once.I Various HTTP extensions proposed by the
`LVVXH PXOWLILOH JHW UHTXHVWV WR JHW DOO WKH ILOHV DW RQFH 9DULRXV +773 H[WHQVLRQV SURSRVHG E\ WKH
`+7731* ZRUNLQJ JURXS DQG DV SDUW RI WKH +773 3LSHOLQLQJ SURSRVDO FDQ EH XVHG WR PDNH WKH
`HTTP—NG working group, and as part of the HTTP Pipelining proposal, can be used to make the
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Response
`from
`
`Receiver
`
`>
`
`
`
`
`%
`
`!
`!
`
`*
`
`(
`"
`
`.
`
`<
`
`!
`
`*
`
`+
`
`#
`
`$
`
`!
`
`!
`
`(
`
`%
`
`
`
`Page 6 of 13
`3DJH  RI 
`
`
`
`
`%
`'
`
`*
`1
`*
`
`requests
`only
`unmatChed
`data
`objects
`
`!
`
`!
`
`)
`
`(
`
`0
`
`%
`
`!
`
`1
`
`!
`
`&
`
`'
`
`"
`
`-
`!
`
`/
`
`,
`.
`
`)
`
`3
`
`!
`
`!
`
`/
`
`"
`
`$
`
`(
`
`)
`
`#
`
`)
`
`"
`
`(
`
`+
`+
`2
`
`/
`
`%\ UHTXHVWLQJ DQ LQGH[ ILOH LW LV SRVVLEOH IRU D FOLHQW WR REWDLQ D FRPSOHWH GHVFULSWLRQ RI WKH VWUXFWXUH
`By requesting an index file it is possible for a client to obtain a complete description of the structure Receiver
`DQG VWDWH RI D VHW RI GDWD ILOHV *LYHQ DQ LQGH[ LW LV SRVVLEOH IRU D FOLHQW WR GHWHUPLQH H[DFWO\ ZKLFK
`and state of a set of data files. Given an index, it is possible for a client to determine exactly which
`ILOHV QHHG WR EH GRZQORDGHG DV ZHOO DV WKH WRWDO VL]H RI WKH GRZQORDG
`
`

`

`
`
`http://www.w3.org/TR/NOTE-drp-19970825
`KWWSZZZZRUJ75127(GUS
`
`GRZQORDG RI PXOWLSOH ILOHV PRUH HIILFLHQW
`download of multiple files more efficient.
`
`1RWH WKDW D FOLHQW FDQ XVH D GLVN FDFKH IRU GDWD ILOHV ZKLFK LV DFFHVVHG XVLQJ FRQWHQW LGHQWLILHUV 7KLV
`Note that a client can use a disk cache for data files, which is accessed using content identifiers. This
`PHDQV WKDW LI PXOWLSOH LQGH[HV UHIHU WR D ILOH ZLWK WKH VDPH FRQWHQW LGHQWLILHU WKH FOLHQW FDQ
`means that if multiple indexes refer to a file with the same content identifier, the client can
`DXWRPDWLFDOO\ GHWHFW WKDW WKH ILOH LV DOUHDG\ LQ WKH FDFKH DQG WKXV DYRLG GRZQORDGLQJ WKH ILOH D VHFRQG
`automatically detect that the file is already in the cache, and thus avoid downloading the file a second
`WLPH 7KLV LV QRW XQFRPPRQ EHFDXVH GLIIHUHQW VLWHV RIWHQ UHIHU WR WKH VDPH VWDQGDUG OLEUDULHV RU LPDJHV
`time. This is not uncommon because different sites often refer to the same standard libraries or images,
`DQG EHFDXVH WKHLU FRQWHQW LGHQWLILHUV PDWFK PXOWLSOH UHGXQGDQW GRZQORDGV FDQ EH DYRLGHG (OLPLQDWLQJ
`and because their content identifiers match, multiple redundant downloads can be avoided. Eliminating
`UHGXQGDQW GRZQORDGV FDQ UHGXFH WKH RYHUKHDG RI GRZQORDGLQJ FRPPRQO\ XVHG GDWD DQG VRIWZDUH
`redundant downloads can reduce the overhead of downloading commonly used data and software
`FRPSRQHQWV 8VLQJ FRQWHQW LGHQWLILHUV LW LV SRVVLEOH WR GHWHFW ZKLFK ILOHV DUH LGHQWLFDO HYHQ LI WKH ILOHV
`components. Using content identifiers it is possible to detect which files are identical, even if the files
`are from different hosts.
`DUH IURP GLIIHUHQW KRVWV
`
`$Q LQGH[ LV QRW UHTXLUHG WR FRQWDLQ D FRQWHQW LGHQWLILHU IRU HDFK ILOH DQG WKH FRQWHQW LGHQWLILHU FDQ EH
`An index is not required to contain a content identifier for each file, and the content identifier can be
`RPLWWHG IRU DQ\ RU DOO RI WKH ILOHV LQ WKH LQGH[ $ VHUYHU FDQ GHFLGH WR RPLW WKH FRQWHQW LGHQWLILHU IRU
`omitted for any or all of the files in the index. A server can decide to omit the content identifier for
`ILOHV WKDW DUH G\QDPLFDOO\ JHQHUDWHG VXFK DV D OLYH YLGHR SLFWXUH ,I QR FRQWHQW LGHQWLILHU LV SUHVHQW WKH
`files that are dynamically generated, such as a live video picture. If no content identifier is present the
`ILOH VKRXOG EH UHWULHYHG XVLQJ D QRUPDO JHWLIPRGLILHG UHTXHVW :KHQ FRPSDULQJ LQGH[HV ILOHV ZLWKRXW
`file should be retrieved using a normal get-if-modified request. When comparing indexes, files without
`D FRQWHQW LGHQWLILHU VKRXOG DOZD\V EH FRQVLGHUHG WR EH GLIIHUHQW
`a content identifier should always be considered to be different.
`
`Content-ID Header Field
`&RQWHQW,' +HDGHU )LHOG
`
`1RZ WKDW LW LV SRVVLEOH WR REWDLQ DQ LQGH[ IRU D ODUJH VHW RI ILOHV D PHFKDQLVP LV QHHGHG WR REWDLQ WKH
`Now that it is possible to obtain an index for a large set of files, a mechanism is needed to obtain the
`FRUUHFW YHUVLRQ RI HDFK RI WKH ILOHV WKDW QHHG GRZQORDGLQJ 1RWH WKDW WKH FRUUHFW YHUVLRQ RI HDFK ILOH LV
`correct version of each of the files that need downloading. Note that the correct version of each file is
`GHWHUPLQHG E\ LWV FRQWHQW LGHQWLILHU DV VSHFLILHG LQ WKH LQGH[ ,W LV YHU\ LPSRUWDQW IRU WKH GLVWULEXWLRQ RI
`determined by its content identifier as specified in the index. It is very important for the distribution of
`DSSOLFDWLRQV WKDW WKH FRUUHFW YHUVLRQ RI HDFK ILOH LV REWDLQHG UDWKHU WKDQ MXVW WKH FXUUHQW YHUVLRQ
`applications that the correct version of each file is obtained, rather than just the current version.
`
`:KHQ UHTXHVWLQJ D ILOH WKH FOLHQW FDQ LQFOXGH WKH FRQWHQW LGHQWLILHU LQ WKH +773 *(7 UHTXHVW WR WKH
`When requesting a file, the client can include the content identifier in the HTTP GET request to the
`VHUYHU )RU H[DPSOH
`server. For example:
`
`
`
`
`G<L /<xample/home.html HTTP/1.1
` *(7 ([DPSOHKRPHKWPO +773
`
` &RQWHQW,' XUQPG3()M:%'YVGDO6%<X;Z
`
` 
`
`Content—ID: urnzmdS:PEFjWBDv/sanlSQBYuXOw==
`the Content-ID field if the correct content identifier is known for the file that is returned.
`
`$ QHZ +773 KHDGHU ILHOG FDOOHG &RQWHQW,' LV XVHG WR VSHFLI\ WKH FRUUHFW YHUVLRQ RI WKH ILOH WKDW LV
`A new HTTP header field called Content-ID is used to specify the correct version of the file that is
`UHTXHVWHG 7KH VHUYHU FDQ XVH WKH FRQWHQWLGHQWLILHU LQ WKH &RQWHQW,' ILHOG VHUYHU WR GHWHUPLQH LI WKH
`requested. The server can use the content-identifier in the Content-ID field server to determine if the
`UHTXHVWHG YHUVLRQ RI WKH ILOH FDQ EH GHOLYHUHG WR WKH FOLHQW
`requested version of the file can be delivered to the client.
`
`7KH FRQWHQW LGHQWLILHU RI WKH UHWXUQHG ILOH VKRXOG EH LQFOXGHG LQ WKH +773 UHSO\ KHDGHU XVLQJ WKH
`The content identifier of the returned file should be included in the HTTP reply header using the
`&RQWHQW,' KHDGHU ILHOG 7KH FRQWHQW LGHQWLILHU LQ WKH UHSO\ PXVW PDWFK WKH UHTXHVWHG FRQWHQW LGHQWLILHU
`Content-ID header field. The content identifier in the reply must match the requested content identifier.
`,I WKH FRUUHFW YHUVLRQ RI WKH ILOH LV QRW DYDLODEOH WKH VHUYHU VKRXOG UHVSRQG ZLWK WKH HUURU  )LOH
`If the correct version of the file is not available, the server should respond with the error: "404 File
`Version Not Found".
`9HUVLRQ 1RW )RXQG
`
`,I QR FRQWHQW LGHQWLILHU LV VSHFLILHG LQ WKH +773 *(7 UHTXHVW WKHQ WKH VHUYHU VKRXOG UHWXUQ WKH FXUUHQW
`If no content identifier is specified in the HTTP GET request, then the server should return the current
`YHUVLRQ RI WKH ILOH DV LV WKH FDVH LQ D QRUPDO +773 UHTXHVW +RZHYHU WKH UHSO\ VKRXOG DOZD\V LQFOXGH
`version of the file, as is the case in a normal HTTP request. However, the reply should always include
`WKH &RQWHQW,' ILHOG LI WKH FRUUHFW FRQWHQW LGHQWLILHU LV NQRZQ IRU WKH ILOH WKDW LV UHWXUQHG
`
`$ VHUYHU WKDW LV XQDZDUH RI WKH &RQWHQW,' ILHOG ZLOO DOZD\V UHSO\ ZLWK WKH FXUUHQW YHUVLRQ RI WKH
`A server that is unaware of the Content-ID field will always reply with the current version of the
`UHTXHVWHG ILOH UHJDUGOHVV RI WKH FRQWHQW LGHQWLILHU VSHFLILHG LQ WKH UHTXHVW 1RWH WKDW WKH VHUYHU LV QRW
`requested file, regardless of the content identifier specified in the request. Note that the server is not
`UHTXLUHG WR VSHFLI\ D &RQWHQW,' LQ WKH UHSO\ DQG WKDW LW LV WKH UHVSRQVLELOLW\ RI WKH FOLHQW WR YHULI\ WKDW
`required to specify a Content-ID in the reply, and that it is the responsibility of the client to verify that
`WKH UHSO\ FRQWDLQV WKH FRUUHFW FRQWHQW LGHQWLILHU LI D &RQWHQW,' ILHOG LV SUHVHQW LQ WKH UHSO\ :KHQ WKH
`the reply contains the correct content identifier if a Content-ID field is present in the reply. When the
`UHTXHVWHG FRQWHQW LGHQWLILHU FRQWDLQV D YHULILDEOH FKHFNVXP 851 WKH FOLHQW VKRXOG DOZD\V UHFRPSXWH
`requested content identifier contains a verifiable checksum URN, the client should always recompute
`the checksum to verify that the correct content was returned.
`WKH FKHFNVXP WR YHULI\ WKDW WKH FRUUHFW FRQWHQW ZDV UHWXUQHG
`
`Page 7 of 13
`3DJH  RI 
`
`
`
`
`
`
`
`
`
`
`
`
`
`00\JChLn$>U0h)P‘
`
`
`
`
`
`  
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`$>$>$>$>$>$>U0U0U0U0U0U0U0U0U0U0h)h)h)h)h)h)h)h)h)h)P‘P‘P‘P‘P‘P‘P‘P‘P‘P‘Ln$>U0h)P‘CDND00\JChLn$>U0h)P‘CDND00\JChLn$>U0h)P‘CDND00\JChLn$>U0h)P‘CDVD
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`(
`
`!
`
`%
`
`+
`
`!
`
`.
`
`%
`
`*
`
`>
`
`%
`
`(
`"
`
`.
`
`<
`
`*
`
`!
`
`#
`
`$
`
`Reply from
`Sender
`
`Response
`from
`
`Receiver
`
`>
`
`
`
`
`%
`
`*
`
`!
`!
`!
`
`!
`
`
`4
`
`<
`
`+
`
`-
`
`,
`
`1
`
`!
`
`

`

`http://www.w3.org/TR/NOTE-drp-19970825
`KWWSZZZZRUJ75127(GUS
`
`2.5 Differential Downloads
` 'LIIHUHQWLDO 'RZQORDGV
`
`:KHQ D ILOH LV XSGDWHG RQ WKH VHUYHU LW ZLOO EH GRZQORDGHG E\ HDFK RI WKH FOLHQWV WKDW QHHGV WKH QHZ
`When a file is updated on the server, it will be downloaded by each of the clients that needs the new
`YHUVLRQ 8SGDWHV WR ILOHV YHU\ RIWHQ DIIHFW RQO\ VPDOO SRUWLRQV RI WKH ILOH DQG LW ZRXOG EH PXFK PRUH
`version. Updates to files very often affect only small portions of the file, and it would be much more
`HIILFLHQW LI WKH VHUYHU FRXOG UHSO\ ZLWK RQO\ WKH SDUWV RI WKH ILOH WKDW KDYH FKDQJHG 7KLV FDQ EH DFKLHYHG
`efficient if the server could reply with only the parts of the file that have changed. This can be achieved
`XVLQJ D GLIIHUHQWLDO *(7 UHTXHVW
`using a differential GET request.
`
`Differential-ID Header Field
`'LIIHUHQWLDO,' +HDGHU )LHOG
`
`Response
`from
`RGCGiVer
`
`$ FOLHQW FDQ XVH WKH LQGH[ REWDLQHG IURP D VHUYHU WR GHWHUPLQH ZKDW FKDQJHV KDYH RFFXUUHG LQ D VHW RI
`A client can use the index obtained from a server to determine what changes have occurred in a set of Receiver
`ILOHV ,W LV DOVR SRVVLEOH WR GHWHFW ZKLFK ILOHV ZHUH PRGLILHG UDWKHU WKDQ FUHDWHG RU GHOHWHG
`files. It is also possible to detect which files were modified, rather than created or deleted.
`requests
`When a file is modified the client can issue a diflerential GET request for the file, which includes not
`only
`:KHQ D ILOH LV PRGLILHG WKH FOLHQW FDQ LVVXH D GLIIHUHQWLDO *(7 UHTXHVW IRU WKH ILOH ZKLFK LQFOXGHV QRW
`only the content identifier of the desired version of the file, but also the content identifier of the current unmatChed
`RQO\ WKH FRQWHQW LGHQWLILHU RI WKH GHVLUHG YHUVLRQ RI WKH ILOH EXW DOVR WKH FRQWHQW LGHQWLILHU RI WKH FXUUHQW
`version of the file on the client.
`data
`YHUVLRQ RI WKH ILOH RQ WKH FOLHQW
`
`
`  
`00\JChLn$>U0b)be
`
`!
`"
`!
`#
`$
`!
`%
`
`!
`(
`<
`(
`!
`*
`+
`objects
`%
`(
`)
`!
`&
`'
`!
`(
`>
`%
`*
`.
`
`
`
`*
`+
`,
`-
`
`!
`"
`!
`#
`$
`!
`%
`
`
`'
`)
`"
`0
`!
`1
`+
`.
`/
`
`
`1
`)
`/
`/
`
`
`!
`"
`)
`(
`*
`2
`3
`
`
`
`
`
`
`
`
`
`
`When the server receives a get request that includes a Differential-ID field, it can look in its file cache Reply from 25
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`?
`@
`A
`B
`C
`D
`E
`F
`G
`
`
`H
`@
`I
`J
`@
`E
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`,Q D GLIIHUHQWLDO *(7 UHTXHVW WKH FRQWHQW LGHQWLILHU RI WKH ILOH WKDW WKH FOLHQW FXUUHQWO\ SRVVHVVHV LV
`In a differential GET request the content identifier of the file that the client currently possesses is
`VSHFLILHG XVLQJ WKH 'LIIHUHQWLDO,' KHDGHU ILHOG )RU H[DPSOH
`specified using the Differential-ID header field. For example:
`
`
`
`
`G<L /<xample/home.html HTTP/1.1
` *(7 ([DPSOHKRPHKWPO +773
`
`Content—ID: urnzmdS:PEFjWBDv/sanlSQBYuXOw==
` &RQWHQW,' XUQPG3()M:%'YVGDO6%<X;Z
`
`Differential—ID: urnzmdS:3FSZoCnWPZptpN050KBemA==
` 'LIIHUHQWLDO,' XUQPG)6R&Q:3=SWS1R.%HP$
`
` 
`
`Sender
`
`26
`27
`28
`
`:KHQ WKH VHUYHU UHFHLYHV D JHW UHTXHVW WKDW LQFOXGHV D 'LIIHUHQWLDO,' ILHOG LW FDQ ORRN LQ LWV ILOH FDFKH
`for both versions of the requested file using the content identifiers specified by the Content-ID field
`IRU ERWK YHUVLRQV RI WKH UHTXHVWHG ILOH XVLQJ WKH FRQWHQW LGHQWLILHUV VSHFLILHG E\ WKH &RQWHQW,' ILHOG
`and the Differential-ID field. If both version of the file are found, the server can compute the
`DQG WKH 'LIIHUHQWLDO,' ILHOG ,I ERWK YHUVLRQ RI WKH ILOH DUH IRXQG WKH VHUYHU FDQ FRPSXWH WKH
`difference between the two files and return the diff rather than the entire file.
`GLIIHUHQFH EHWZHHQ WKH WZR ILOHV DQG UHWXUQ WKH GLII UDWKHU WKDQ WKH HQWLUH ILOH
`
`:KHQ D VHUYHU UHSOLHV ZLWK D GLIIHUHQWLDO XSGDWH LW PXVW LQFOXGH ERWK WKH FRQWHQW LGHQWLILHU RI WKH
`29 When a server replies with a differential update, it must include both the content identifier of the
`UHVXOWLQJ ILOH LQ WKH &RQWHQW,' ILHOG DV ZHOO DV WKH FRQWHQW LGHQWLILHU RI WKH ILOH WR ZKLFK WKH XSGDWH
`resulting file in the Content-ID field, as well as the content identifier of the file to which the update
`30
`VKRXOG EH DSSOLHG LQ WKH 'LIIHUHQWLDO,' ILHOG
`31
`should be applied in the Differential-ID field.
`
`32
`33
`34
`
`36
`37
`
`40
`41
`
`43
`
`If the server does not have access to the version of the file that is indicated by the differential content
`,I WKH VHUYHU GRHV QRW KDYH DFFHVV WR WKH YHUVLRQ RI WKH ILOH WKDW LV LQGLFDWHG E\ WKH GLIIHUHQWLDO FRQWHQW
`LGHQWLILHU LW FDQ LJQRUH WKH GLIIHUHQWLDO FRQWHQW LGHQWLILHU DQG UHWXUQ WKH HQWLUH UHTXHVWHG ILOH $OVR LI
`identifier, it can ignore the differential content identifier, and return the entire requested file. Also, if
`WKH GLII LV QRW VPDOOHU WKH VHUYHU FDQ GHFLGH WR WKH VHQG WKH HQWLUH ILOH LQVWHDG
`the diff is not smaller, the server can decide to the send the entire file instead.
`
`$ FOLHQW FDQ GHWHFW ZKHQ D GLIIHUHQWLDO XSGDWH LV UHWXUQHG E\ H[DPLQLQJ WKH PLPH W\SH RI WKH UHSO\
`A client can detect when a differential update is returned by examining the mime type of the reply.
`After verifying the Content-ID and Differential-ID fields in the reply, the client can apply the diff to its
`$IWHU YHULI\LQJ WKH &RQWHQW,' DQG 'LIIHUHQWLDO,' ILHOGV LQ WKH UHSO\ WKH FOLHQW FDQ DSSO\ WKH GLII WR LWV
`FXUUHQW YHUVLRQ RI WKH ILOH WR JHQHUDWH WKH GHVLUHG YHUVLRQ RI WKH ILOH
`current version of the file to generate the desired version of the file.
`
`7R HQVXUH LQWHURSHUDELOLW\ LW LV QHFHVVDU\ WR VSHFLI\ D ZHOO NQRZQ IRUPDW ZKLFK FDQ EH XVHG WR GHVFULEH
`To ensure interoperability it is necessary to specify a well known format which can be used to describe
`WKH GLIIHUHQFHV EHWZHHQ WZR YHUVLRQ RI DQ\ ILOH 7KH GHIDXOW GLII IRUPDW LV WKH *',)) IRUPDW ZKLFK LV
`the differences between two version of any file. The default diff format is the GDIFF format which is
`defined in a separate proposal. The client can specify additional acceptable differencing formats using
`GHILQHG LQ D VHSDUDWH SURSRVDO 7KH FOLHQW FDQ VSHFLI\ DGGLWLRQDO DFFHSWDEOH GLIIHUHQFLQJ IRUPDWV XVLQJ
`WKH $FFHSW KHDGHU ILHOG
`the Accept header field.
`
`$ VLPSOH VHUYHU FDQ FKRRVH WR LJQRUH GLIIHUHQWLDO JHW UHTXHVWV DOWRJHWKHU DQG VLPSO\ UHSO\ ZLWK WKH
`A simple server can choose to ignore differential get requests altogether, and simply reply with the
`HQWLUH FRQWHQWV RI WKH UHTXHVWHG ILOH
`entire contents of the requested file.
`
`45
`
`Note that although the example uses the Content-ID field to specify the desired version of a file, this
`1RWH WKDW DOWKRXJK WKH H[DPSOH XVHV WKH &RQWHQW,' ILHOG WR VSHFLI\ WKH GHVLUHG YHUVLRQ RI D ILOH WKLV
`
`Page 8 of 13
`3DJH  RI 
`
`

`

`http://www.w3.org/TR/NOTE-drp-19970825
`KWWSZZZZRUJ75127(GUS
`
`ILHOG FDQ EH RPLWWHG LQ RUGHU WR REWDLQ D GLIIHUHQWLDO XSGDWH WR WKH PRVW UHFHQW YHUVLRQ 7KH VHUYHU
`field can be omitted in order to obtain a differential update to the most recent version. The server
`VKRXOG UHWXUQ D  1RW 0RGLILHG UHSO\ LI WKH UHTXHVWHG UHVRXUFH KDV QRW FKDQJHG
`should return a "304 Not Modified" reply if the requested resource has