' $ 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 cartoons, ...) • URLs, URNs: not always a single file (ASCII, HTML; English, French) • resolution of URN may be time-dependent (current weather map) directory,hints • URN URLs, URCs → • examples: ISBN, MIME content-ids (cid) & % April 21, 1998
' $ URN 3 Uniform Resource Characteristics (URC) meta information: • bibliographic citation • digital signature • revision history ➠ not currently available & % April 21, 1998
' $ URN 4 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
' $ URN 5 URN resolution • single directory won’t scale • typical: local hints for resolution • fallback: URN-resolution-service discovery service (UDS) & % April 21, 1998
' $ URN 6 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
' $ URN 7 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
' $ URN 8 NAPTR: Example 1: one-stage resolution Dunn and Bradstreet company identifiers: duns.urn.net ;; order 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
' $ URN 9 NAPTR: Example 2: two-stage resolution MIME content identifiers, e.g., urn:cid:199606121851.1@mordred.gatech.edu : cid.urn.net ;; order pref flags service regexp replacement IN NAPTR 100 10 "" "" "/.+@([ˆ@]+)/\1/i" . no “terminal” flag ➠ mordred.gatech.edu NAPTR *.gatech.edu IN NAPTR ;; order 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
' $ URN 10 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 ;; order 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
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