Best Practices OGC URNs

Introduction

A URN or Unique Resource Identifier is a scheme that serves as unique string identifiers for concepts (units, phenomena) or real word objects (documents). OGC has defined a URN scheme to help identify better terminology used in request and responses of there services.

General and Recommended Form

Considerations

Terms could have more than one representation (like EPSG codes)

If there is no version then the version string is null and a colon may appear after another colon. For example: urn:ogc:def:crs:EPSG::4326. OGC URN Policy and 07-092r1 are not very clear. We assume that in the case of OGC definitions: "urn:ogc:def" ":" objectType ":" authority ":" [ version ] ":" code, there must be at least six ":", where:

• Between the 5th and 6th colon it is encounter the version string
• After the 6th colon it is encounter the version number, and it could contain colons.

Concatenating URNs

Commonly use terms

Making your definitions officially an OGC URN

If an organization wants its definitions to have the OGC namespace, then they must submit a OGC URN {ResourceSpecificString} proposal to the OGC naming authority. More information is available in the OGC URN Policy Governance section.

OGC URN Scheme in EBNF

This section presents the OGC URN scheme in Extended Backus–Naur (EBNF) form, that is assumed by OOSTethys. The following documents were used as source:

• URN Scheme RFC 2141 http://www.rfc-editor.org/rfc/rfc2141.txt
• OGC URN Policy: http://www.opengeospatial.org/ogcUrnPolicy
• OGC #07-092r1: http://portal.opengeospatial.org/files/?artifact_id=24045

Note: There is no a complete BNF (Backus-Naur Form) or EBNF currently defined in any OGC official document. The URN syntax representation presented here is for OOSTethys summary purposes and to help developers code appropriately.

URN ::= "urn:ogc:" OGCResourceType

OGCResourceType ::= OGCDefintionType | OGCSpecificationType | OGCServiceType

OGCDefintionType ::= "def:" objectType ":" authority ":" (version)? ":" code

OGCSpecificationType ::= To be defined

OGCServiceType ::= To be defined

objectType ::= "axis" | "axisDirection" | "coordinateOperation" | "crs" | "cs" | "datum" | "dataType" | "derivedCRSType" | "documentType" | "ellipsoid" | "featureType" | "group" | "meaning" | "meridian" | "method" | "nil" | "parameter" | "phenomenon" | "pixelInCell" | "rangeMeaning" | "referenceSystem" | "uom" | "verticalDatumType"

authority ::= "ECSD" | "EPSG" | "OGC" | "SI" | "UCUM"

version ::= (URNChars) +

code ::= (URNChars | ":") +

URNChars ::= trans | "%"

hex ::= number | "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f"

trans ::= letter | number | other | reserved

letter ::= upper | lower

upper ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"

lower ::= "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"

number ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

other ::= "(" | ")" | "+" | "," | "-" | "." | ":" | "=" | "@" | ";" | "$" | "_" | "!" | "*" | "'"

reserved ::= "%" | "/" | "?" | "#"

Revision History

TODOs