Uniform Resource Names (URNs) & % April 21, 1998 ' $ URN - - PowerPoint PPT Presentation

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' $ URN 1 Uniform Resource Names (URNs) & % April 21, 1998 ' $ URN 2 URNs persistent resource identifiers (names) URLs = location for long-lived resources (papers, newspaper article archives, legal records, Dilbert

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Uniform Resource Names (URNs)

April 21, 1998

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URNs

persistent resource identifiers (names) ↔ URLs = location
for long-lived resources (papers, newspaper article archives, legal

records, Dilbert cartoons, ...)

URLs, URNs: not always a single file (ASCII, HTML; English,

French)

resolution of URN may be time-dependent (current weather map)
URN

directory,hints

→ URLs, URCs

examples: ISBN, MIME content-ids (cid)

April 21, 1998

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Uniform Resource Characteristics (URC)

meta information:

bibliographic citation
digital signature
revision history

➠ not currently available

April 21, 1998

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URN syntax

[urn:] <NID> ":" <NSS> NID: namespace identifier (ISBN) NSS: namespace specific syntax Examples (fictional): urn:isbn:1-23485-8-29 cid:foo@huh.com

April 21, 1998

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URN resolution

single directory won’t scale
typical: local hints for resolution
fallback: URN-resolution-service discovery service (UDS)

April 21, 1998

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HTTP for URN resolution

services

N2L: URN → URL: 302 Moved temporarily N2Ls: URN → URLs: <LI> URLs N2R: URN → resource N2C: URN → URC N2Ns: URN → current URN L2Ns: URL → URNs GET /uri-res/N2L/cid:foo@huh.com HTTP/1.0

April 21, 1998

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DNS as URN directory

new DNS resource record (RR): naming authority pointer (NAPTR)
create new domain: NID + .urn.net
works with DNS SRV records = generalization of MX records ➠

map service + domain to host(s), ports and protocol (RFC 2052)

try host cid.urn.net – works!

April 21, 1998

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NAPTR: Example 1: one-stage resolution

Dunn and Bradstreet company identifiers:

duns.urn.net ;;

rder pref flags service

regexp replacement IN NAPTR 100 10 "s" "dunslink+N2L+N2C" "" dunslink.udp.isi.dandb.com IN NAPTR 100 20 "s" "rcds+N2C" "" rcds.udp.isi.dandb.com IN NAPTR 100 30 "s" "http+N2L+N2C+N2R" "" http.tcp.isi.dandb.com

order (for delegation) and preference (for performance) ➠ resolution

sequence

flag: ”s” ➠ SRV (service) records, ”a” ➠ A records
➠ use RCDS to look up

;; Pref Weight Port Target rcds.udp.isi.dandb.com IN SRV 0 0 1000 defduns.isi.dandb.com IN SRV 0 0 1000 dbmirror.com.au IN SRV 0 0 1000 ukmirror.com.uk

➠ three redundant servers

April 21, 1998

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NAPTR: Example 2: two-stage resolution

MIME content identifiers, e.g., urn:cid:199606121851.1@mordred.gatech.edu:

cid.urn.net ;;

rder pref flags service

regexp replacement IN NAPTR 100 10 "" "" "/.+@([ˆ@]+)/\1/i" .

no “terminal” flag ➠ mordred.gatech.edu NAPTR

*.gatech.edu IN NAPTR ;;

rder pref flags servic

regexp replacement IN NAPTR 100 50 "s" "z3950+N2L+N2C" "" z3950.tcp.gatech.edu. IN NAPTR 100 50 "s" "rcds+N2C" "" rcds.udp.gatech.edu. IN NAPTR 100 50 "s" "http+N2L+N2C+N2R" "" http.tcp.gatech.edu.

April 21, 1998

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NAPTR: Example 3: http mirroring

http://www.foo.com/software/latest-beta.exe

http.urn.net IN NAPTR ;; order pref flags service regexp replacement 100 90 "" "" "/.*\/\/([ˆ\/:]+)/\1/i" .

➠ return everything after the first double slash ➠ www.foo.com

www.foo.com ;;

rder pref flags service regexp replacement

IN NAPTR 100 100 "s" "http+L2R" "" http.tcp.foo.com IN NAPTR 100 100 "s" "ftp+L2R" "" ftp.tcp.foo.com

April 21, 1998