Network Working Group J. Wackerow
Internet Draft DDI Alliance
Intended status: Informational February 23, 2021
Expires: August 2021
A Uniform Resource Name (URN) Namespace for the
Data Documentation Initiative (DDI)
draft-urn-ddi-00.txt
Abstract
This document describes the Namespace Identifier (NID) "ddi" for
Uniform Resource Names (URNs) used to identify resources that conform
to the standards published by the Data Documentation Initiative (DDI)
Alliance (https://ddialliance.org/).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF). Note that
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 27, 2021.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................3
3. Specification..................................................4
3.1. Namespace ID..............................................4
3.2. Registration Information..................................4
3.3. Declared Registrant of the Namespace......................4
3.4. Declaration of Syntactic Structure........................4
3.4.1. Description..........................................4
3.4.2. ABNF Grammar.........................................5
3.4.3. Regular Expression...................................7
3.4.4. Examples of DDI URNs.................................8
3.5. Relevant Ancillary Documentation..........................8
3.6. Identifier Uniqueness Considerations......................9
3.7. Identifier Persistence Considerations.....................9
3.8. Process of Identifier Assignment..........................9
3.9. Process for Identifier Resolution.........................9
3.10. Rules for Lexical Equivalence...........................10
3.11. Conformance with URN Syntax.............................11
3.12. Validation Mechanism....................................11
3.13. Scope...................................................11
4. Namespace Considerations......................................11
4.1. URN Assignment Procedures................................11
4.2. URN Resolution/Delegation................................11
4.3. Type of Resources to be Identified.......................11
4.4. Type of Services.........................................11
5. Community Considerations......................................12
5.1. Open Assignment and Use of Identifiers...................12
5.2. Open Operation of Resolution Servers.....................12
5.3. Creation of Software for Service Discovery...............12
6. IANA Considerations...........................................13
7. Security Considerations.......................................13
8. References....................................................13
8.1. Normative References.....................................13
8.2. Informative References...................................15
9. Acknowledgments...............................................17
Appendix A. Example DNS Records..................................18
A.1. Delegation of the URN Namespace "ddi"....................18
A.2. Delegation of DDI Agencies...............................18
A.3. DDI Services.............................................18
Appendix B. Algorithm for DDI Service Discovery..................20
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1. Introduction
This document registers a formal namespace identifier (NID) for
Uniform Resource Names [RFC8141] associated with DDI resources in
accordance with the process defined in [RFC8141].
The DDI Alliance is an international collaboration dedicated to
establishing metadata standards and semantic products for describing
social science data, data covering human activity, and other data
based on observational methods. DDI specifications are free standards
that can document and manage different stages in the research data
lifecycle, such as conceptualization, collection, processing,
distribution, discovery, and archiving. Documenting data with DDI
facilitates understanding, interpretation, and use -- by people,
software systems, and computer networks.
The specifications DDI Codebook [DDIC] and DDI Lifecycle [DDIL] are
expressed in XML Schema, DDI XKOS - Extended Knowledge Organization
System [DDIXKOS] in OWL/RDF, SDTL - Structured Data Transformation
Language [SDTL] in JSON Schema, and the upcoming DDI - Cross Domain
Integration (DDI-CDI) in UML. DDI is aligned with other metadata
standards like Dublin Core Metadata Initiative [DUBLINC], Statistical
Data and Metadata Exchange [SDMX] for exchanging aggregate data,
ISO/IEC 11179 [IS11179] for building metadata registries such as
question, variable, and concept banks, and ISO 19115 [IS19115] for
supporting geographic information systems.
DDI URNs support reusability of DDI resources inside a single DDI
instance and in a distributed network of DDI instances.
The DDI specification is developed and maintained by the DDI Alliance
[DDIALL]. The DDI Alliance is a self-sustaining membership
organization whose over 40 member institutions have a voice in the
development of the DDI specifications.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC 2119 significance.
"DDI": Data Documentation Initiative. The single term is often used
as a synonym for the DDI specification.
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"DDI agency": An organization which maintains DDI resources.
"DDI Alliance": Alliance for the Data Documentation Initiative (DDI).
"RFC": The basic publication series for the IETF. RFCs are published
by the RFC Editor and once published are never modified ([RFC2026]
section 2.1).
3. Specification
This section provides the information required to register a formal
namespace according to the registration procedure defined in
[RFC8141]. The URNs conform to the syntax defined in [RFC8141].
3.1. Namespace ID
The Namespace Identifier (NID) "ddi" is requested.
3.2. Registration Information
Version 1
Date: February 23, 2021
3.3. Declared Registrant of the Namespace
Name: The Data Documentation Initiative Alliance (DDI Alliance)
Address: ICPSR, University of Michigan
PO Box 1248
Ann Arbor, MI 48106-1248
USA
Website: ddialliance.org
Contact: Joachim Wackerow
E-mail: joachim.wackerow@posteo.de,
secretariat@ddialliance.org
3.4. Declaration of Syntactic Structure
3.4.1. Description
The Namespace Specific String (NSS) of all URNs using the "ddi" NID
is a globally unique identifier consisting of the DDI agency
identifier (registration authority identifier), the identifier of the
DDI resource (data identifier), and the version of the resource
(version identifier) [DDIID]. This structure is according to the
International Registration Data Identifier (IRDI) defined in ISO/IEC
11179 Information technology - Metadata registries (MDR) - Part 6:
Registration, Annex A [IS11179].
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A description of the DDI resource identification is available in the
DDI Lifecycle (3.3) Technical Guide, section Identification [DDIID].
The DDI NSS has the following structure:
<agency-identifier>:<resource-identifier>:<version-identifier>
agency-identifier is the identifier of a DDI agency that maintains
DDI resources. This identifier basically follows the rules of
reversed domain names and is case-insensitive. This way, the DNS
resolution of DDI agency identifiers is supported. The hierarchy of
domains descends from the left to the right label in the name; each
label to the right specifies a subdivision, or subdomain of the
domain to the left. The left-most label of agency-identifier conveys
the top-level domain. It SHALL be a country code corresponding to ISO
3166 alpa-2 codes [ISO3166] or another top-level domain maintained by
IANA [TLD]. All two-letter top-level domains are reserved for current
and future ISO 3166 codes. Assignment of identifiers for DDI agencies
in the requested namespace is managed by the DDI Alliance (see
section 3.8. on "Process of Identifier Assignment"). The next
subdomain identifies the agency within that top-level domain. Further
optional subdomains can follow. The top-level domain and possible
subdomains are separated by the full stop character. The full stop
character is not allowed within top-level domain names or subdomain
names. The top-level domain and subdomains are composed from the
limited set of characters for the preferred form of a DNS label
([RFC1035] section 2.3.1). The length of the label and the full name
are restricted by DNS rules ([RFC2181] section 11). The agency
identifier is case insensitive ([RFC4343] section 2).
resource-identifier is the identifier of a DDI resource of a DDI
agency. The value MUST be unique in the scope of this DDI agency. The
resource identifier is case sensitive.
version-identifier is the version of a DDI resource of a DDI agency.
The value MUST be unique in the scope of this resource. The resource
version is case sensitive.
3.4.2. ABNF Grammar
The following syntax specification for the complete URN uses the
augmented Backus-Naur Form (ABNF) as described in [RFC5234].
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ABNF Grammar
; Rules are case-sensitive, if not stated otherwise.
ddi-urn = urn separator ddi separator ddi-irdi
; urn is case-insensitive, see [RFC8141].
urn = "urn"
; ddi is the URN namespace identifier.
; ddi is case-insensitive, see [RFC8141] section 2.1.
ddi = "ddi"
; ddi-irdi is the namespace specific string (NSS).
; ddi-irdi - international registration data identifier,
; see [IS11179] Annex A.2.
ddi-irdi = agency-identifier separator
resource-identifier separator
version-identifier
; agency-identifier is case-insensitive. See [RFC4343] section 2.
; For allowed characters see [RFC1035] section 2.3.1.
; For length restrictions see [RFC2181] section 11.
agency-identifier = top-level-domain
sub-separator ddi-authority-id
*(sub-separator ddi-sub-authority-id)
; length limit is 255 characters
; see section 11 of [RFC2181]
top-level-domain = dns-label
ddi-authority-id = dns-label
ddi-sub-authority-id = dns-label
dns-label = (ALPHA / DIGIT)
[ *(ALPHA / DIGIT / "-")
(ALPHA / DIGIT) ]
; length limit is 63 characters
; see section 11 of [RFC2181]
resource-identifier = restricted-string
*("/" restricted-string)
version-identifier = restricted-string
*("/" restricted-string)
restricted-string = 1*(unreserved / sub-delims / "@")
; Definitions for unreserved and sub-delims from [RFC3986] 2.2.
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")" /
"*" / "+" / "," / ";" / "="
separator = ":"
sub-separator = "."
; ALPHA and DIGIT are actually defined in the ABNF specification.
; They are declared here for convenience purposes.
ALPHA = %x41-5A / ; uppercase letters
%x61-7A ; lowercase letters
DIGIT = %x30-39 ; digits
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3.4.3. Regular Expression
The used syntax is the XML Schema flavor which can be easily used in
other flavors. These regular expressions implicitly anchor at the
head and tail. The following regular expression syntax uses
components (component names indicated by angle brackets, i.e.
<component>) and is written in free-spacing mode for easier reading
(the XML Schema flavor does not support that). Please note that use
of multiple quantifiers in regular expressions can result in false
outcomes due to so-called greediness. Therefore, there are separate
regular expressions for the length restriction and other purposes for
the components agency-identifier and dns-label.
ddi-urn := [Uu][Rr][Nn] : [Dd][Dd][Ii] :
<agency-identifier> :
<resource-identifier> :
<version-identifier>
agency-identifier := <top-level-domain> \.
<ddi-authority-id>
(\. <ddi-sub-authority-id>)*
agency-identifier := .{1,255}
top-level-domain := <dns-label>
ddi-authority-id := <dns-label>
ddi-sub-authority-id := <dns-label>
dns-label := [A-Za-z0-9]([-A-Za-z0-9]*[A-Za-z0-9])?
dns-label := .{1,63}
resource-identifier := <restricted-string>
(/ <restricted-string>)*
version-identifier := <restricted-string>
(/ <restricted-string>)*
restricted-string := [A-Za-z0-9-._~!$&'()*+,;=@]+
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3.4.4. Examples of DDI URNs
The examples are taken from the DDI Lifecycle 3.3. documentation.
Please note that the resource identifiers are simplified. In real
applications, they are much longer for unique identification
purposes. They don't relate to DDI types like the examples might
suggest.
URN of a Represented Variable
urn:ddi:us.ddia1:R-V1:1
The DDI represented variable identified by "R-V1" with the version
"1" of the DDI agency "ddia1" located in the domain "us" [DDIEXRV].
URN of a Question Item
urn:ddi:us.ddia1:PISA-QS.QI-2:1
The DDI question item identified by "PISA-QS.QI-2" with the version
"1" of the DDI agency "ddia1" in the domain "us" [DDIEXQU].
URN as Reference to a Controlled Vocabulary
urn:ddi:int.ddi.cv:AggregationMethod:1.0
The DDI controlled vocabulary identified by "AggregationMethod" with
the version "1.0" in the scope of the DDI agency "ddi" and sub-agency
"cv" in the domain "int" [DDICVAG].
3.5. Relevant Ancillary Documentation
An introductory article on DDI can be found at [DDIINTR].
Information on the DDI specifications (DDI-C, DDI-L, XKOS, Controlled
Vocabularies, and SDTL) can be found in the standards section of the
DDI Alliance website [DDIALL].
Information on domain names can be found in the relevant RFCs.
o For an overview, see [RFC1034].
o Regarding case insensitivity, see [RFC1035] section 2.3.3.
o Regarding syntax, see [RFC952] section "Grammatical Host Table
Specification" B. and [RFC1123] section 2.1.
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o Regarding size limits, see [RFC1123] section 2.1 and [RFC1035]
section 2.3.4.
3.6. Identifier Uniqueness Considerations
Assignment of identifiers for DDI agencies in the requested namespace
will be managed by the DDI Alliance, which will ensure that the
assigned DDI agency identifiers are consistent with the directives
for unique identification of DDI agencies.
Assignment of URNs for resources of a DDI agency in the requested
namespace will be managed by the respective DDI agency, which ensures
that the assigned URNs are unique for the scope of the agency.
3.7. Identifier Persistence Considerations
Persistence of identifiers is dependent upon suitable delegation of
resolution at the level of the DDI agencies, and persistence of DDI
agency assignment. The persistence of the referenced resource is also
the responsibility of the DDI agency.
3.8. Process of Identifier Assignment
Assignment of identifiers for DDI agencies in the requested
namespaceis managed by the DDI Alliance. A registry for DDI agency
identifiers ensures through an approval process that the syntax of
agency identifiers complies with the associated rules [DDIREGI].
Assignment of URNs for resources of a DDI agency and sub-agencies of
a DDI agency in the requested namespace will be managed by the
respective DDI agency.
3.9. Process for Identifier Resolution
The DDI Alliance will promote a service discovery system for
identifying available services connected to DDI agencies using the
Domain Name System (DNS). A DNS request for a DDI agency within the
domain ddi.urn.arpa is delegated by the DNS servers of the DDI
Alliance to the DNS servers of the relevant DDI agency. The response
is a list of available DDI services for the agency identifier under
which the agency has assigned URNs. The approach is based on the
Dynamic Delegation Discovery System (DDDS) [RFC3401] and especially
the straightforward URI-enabled NAPTR (U-NAPTR) [RFC4848].
The DDI Alliance is responsible for operating or delegating
resolution requests to the resolution servers of the relevant DDI
agencies. DDI agencies are responsible for operating or delegating
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resolution servers for the agency identifier under which they have
assigned URNs.
Sample Sequence Diagram for receiving a list of DDI services from the
example DDI agency "ddia1".
Client NS for NS for NS for DDI services
urn.arpa ddialliance.org example1.edu for us.ddia1
| | | | |
1 |------>| | | |
2 |<------| | | |
3 |---------------------->| | |
4 |<----------------------| | |
5 |-------------------------------------->| |
6 |<--------------------------------------| |
7 |------------------------------------------------------>|
8 |<------------------------------------------------------|
1. The name server (NS) of IANA for the domain "urn.arpa." is
reached with the request "ddia1.us.ddi.urn.arpa." for the
DDI agency "us.ddia1".
2./3. The request is delegated to the name server for
"ddialliance.org".
4./5. The request is delegated to the name server for
"example1.edu" (domain of the DDI agency "us.ddia1").
6. The server responds with a list of NAPTR records [RFC3403]
pointing to available DDI services for the DDI agency
"us.ddia1".
7. The client selects an appropriate DDI service and sends a
request for a DDI URN to this service.
8. The DDI service responds for example with a DDI object
identified by the requested DDI URN.
See Appendix A for examples of name server records.
3.10. Rules for Lexical Equivalence
The DDI agency identifier basically follows the rules of domain
names. Domain names are case-insensitive. Thus, the portion of the
URN
urn:ddi:<agency-id>:
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is case-insensitive for matches. The remainder of the identifier MUST
be considered case-sensitive.
3.11. Conformance with URN Syntax
The Namespace Specific String conforms to the related section in
[RFC8141]. It is composed from the limited set of characters for an
URN NSS [RFC8141]. Percent encoding is not used.
3.12. Validation Mechanism
The DDI Alliance will promote development of software for validation
purposes.
3.13. Scope
The scope is global.
4. Namespace Considerations
There is no available namespace that will allow one to uniquely
identify and access DDI resources.
4.1. URN Assignment Procedures
See also above section on Process of Identifier Assignment.
4.2. URN Resolution/Delegation
See also above section on Process for Identifier Resolution.
It is RECOMMENDED to use sub-agencies for flexible administration.
For example, delegation of URNs of a sub-agency to different servers
would be easily possible.
4.3. Type of Resources to be Identified
The DDI specifications define resources at a granular level, many of
which can be identified by a DDI URN.
4.4. Type of Services
Examples of potential services are listed below. The services and
appropriate service tags need to be defined in future. The mentioned
service tags are from [RFC2169].
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o DDI repository
o N2R: given a DDI URN return one instance of the resource
identified by that URN.
o DDI registry
o N2C: given a DDI URN return a description or a summary of that
resource.
o DDI URN resolution
o N2L: given a DDI URN return one URL that identifies a location
where the identified DDI resource can be found.
o N2Ls: given a DDI URN return one or more URLs that identify
multiple locations of the identified DDI resource.
5. Community Considerations
5.1. Open Assignment and Use of Identifiers
DDI agency identifiers can be registered at the DDI Alliance. The DDI
Alliance will maintain a registry of the assigned values for the DDI
agency identifier used in the NSS. Information may be obtained from
the following address: secretariat@ddialliance.org.
DDI agencies assign URNs and potential sub-agencies within the scope
of the assigned DDI agency identifiers.
See also above section on Identifier Uniqueness Considerations.
5.2. Open Operation of Resolution Servers
The DDI Alliance operates publicly accessible name servers for the
delegation of DNS requests within the domain ddi.urn.arpa to DNS
servers of DDI agencies.
5.3. Creation of Software for Service Discovery
The DDI Alliance will promote software for the resolution of DDI
agency identifiers and service discovery. See also Appendix B for the
resolution algorithm. A basic resolver library is available
[DDIRESO].
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6. IANA Considerations
This document defines an URN NID registration of "ddi". IANA is asked
to register "ddi" in the URN Namespaces registry.
The registration for "ddi" in the "URN.ARPA" zone is planned.
Requests for the domain ddi.urn.arpa will be delegated to the name
servers of the DDI Alliance.
7. Security Considerations
This document introduces no additional security considerations beyond
those associated with the use and resolution of URNs in general.
The security of the DNS-based resolution of DDI agency identifiers is
only as good as the security of DNS queries in general. A full
discussion of the security threats pertaining to DNS and possible
solutions can be found in [RFC3833]. Further information on security
considerations regarding U-NAPTR can be found in [RFC4848] section 6.
8. References
8.1. Normative References
[DDIC] DDI Codebook, DDI Alliance 2000-2014,
<https://ddialliance.org/Specification/DDI-Codebook/>.
[DDIL] DDI Lifecycle, DDI Alliance 2009-2020,
<https://ddialliance.org/Specification/DDI-Lifecycle/>.
[DDIXKOS] DDI XKOS - Extended Knowledge Organization System, DDI
Alliance 2020,
<https://ddialliance.org/Specification/RDF/XKOS>.
[DDIID] DDI Lifecycle (3.3) Technical Guide, Identification,
<https://ddi-lifecycle-technical-
guide.readthedocs.io/en/latest/General%20Structures/Identif
ication.html>.
[RFC952] Harrenstien, K., Stahl, M., and E. Feinler "DoD Internet
Host Table Specification", RFC 952, October 1985,
<https://www.rfc-editor.org/info/rfc952>.
[RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities",
RFC 1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
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[RFC1035] Mockapetris, P., "Domain Names - Implementation and
Specification", RFC 1035, November 1987,
<https://www.rfc-editor.org/info/rfc1035>.
[RFC1123] Braden, R., Ed. "Requirements for Internet Hosts --
Application and Support", RFC 1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996,
<https://www.rfc-editor.org/info/rfc2026>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997,
<https://www.rfc-editor.org/info/rfc2181>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", RFC 3986,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4343] Eastlake, D. 3rd, "Domain Name System (DNS) Case
Insensitivity Clarification", RFC 4343, January 2006,
<https://www.rfc-editor.org/info/rfc4343>.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5378] Bradner, S. and J. Contreras, "Rights Contributors Provide
to the IETF Trust", BCP 78, RFC 5378, November 2008,
<https://www.rfc-editor.org/info/rfc5378>.
[RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", RFC 8141, April 2017,
<https://www.rfc-editor.org/info/rfc8141>.
[RFC8179] Bradner, S. and J. Contreras, "Intellectual Property Rights
in IETF Technology", BCP 79, RFC 8179, May 2017,
<https://www.rfc-editor.org/info/rfc8179>.
[SDTL] SDTL - Structured Data Transformation Language - Version
1.0, <https://ddialliance.org/products/sdtl/1.0/>.
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[TLD] IANA Database of Top Level Domains,
<https://www.iana.org/domains/root/db>.
8.2. Informative References
[ABNF2RS] ABNF to REGEX Regular Expression Generator, Michael R.
Sweet, <https://www.msweet.org/abnf/>.
[ABNFGEN] abnfgen, Jutta Degener, <http://www.quut.com/abnfgen/>.
[ABNFPFE] ABNF Parser, Bill Fenner,
<http://tools.ietf.org/tools/bap/abnf.cgi>.
[DDIALL] DDI Alliance, <https://ddialliance.org/>.
[DDICVAG] DDI Controlled Vocabulary for Aggregation Method,
<https://ddialliance.org/Specification/DDI-
CV/AggregationMethod_1.0.html>.
[DDIEXQU] DDI Lifecycle 3.3 Technical Guide, Examples, Questions,
<https://ddi-lifecycle-technical-
guide.readthedocs.io/en/latest/Examples/Questions.html>.
[DDIEXRV] DDI Lifecycle 3.3 Technical Guide, Examples, Represented
Variable, <https://ddi-lifecycle-technical-
guide.readthedocs.io/en/latest/Examples/RepresentedVariable
.html>.
[DDIINTR] Vardigan, M., Heus, P., and W. Thomas. "Data Documentation
Initiative: Toward a Standard for the Social Sciences." The
International Journal of Digital Curation 3, 1 (2008),
<http://www.ijdc.net/article/view/66>.
[DDIREGI] DDI Agency Registry, <https://registry.ddialliance.org/>.
[DDIRESO] DDI Agency Registry Tools,
<https://registry.ddialliance.org/Home/Tools>.
[DUBLINC] Dublin Core Metadata Initiative,
<https://www.dublincore.org/>.
[ISO3166] ISO 3166 Country Codes,
<https://www.iso.org/iso-3166-country-codes.html>.
[IS11179] ISO/IEC 11179 Information technology - Metadata registries
(MDR) - Part 6: Registration,
<http://metadata-standards.org/11179/>.
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[IS19115] ISO 19115, Geographic information -- Metadata,
<https://www.iso.org/standard/26020.html>.
[RFC2169] Daniel, R., "A Trivial Convention for using HTTP in URN
Resolution", RFC 2169, June 1997,
<https://www.rfc-editor.org/info/rfc2169>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000, <https://www.rfc-editor.org/info/rfc2782>.
[RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS) -
Part Two: The Algorithm", RFC 3401, October 2002,
<https://www.rfc-editor.org/info/rfc3401>.
[RFC3402] Mealling, M., "Dynamic Delegation Discovery System (DDDS) -
Part Two: The Algorithm", RFC 3402, October 2002,
<https://www.rfc-editor.org/info/rfc3402>.
[RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS) -
Part Three: The Domain Name System (DNS) Database", RFC
3403, October 2002,
<https://www.rfc-editor.org/info/rfc3403>.
[RFC3833] Atkins, D. and R. Austein, "Threat Analysis Of The Domain
Name System", RFC 3833, August 2004,
<https://www.rfc-editor.org/info/rfc3833>.
[RFC3958] Daigle, L., Newton, A., "Domain-Based Application Service
Location Using SRV RRs and the Dynamic Delegation Discovery
Service (DDDS)", RFC 3958, January 2005,
<https://www.rfc-editor.org/info/rfc3958>.
[RFC4848] Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007,
<https://www.rfc-editor.org/info/rfc4848>.
[RFC5385] Touch, J, "Version 2.0 Microsoft Word Template for Creating
Internet Drafts and RFCs", RFC 5385, February 2010,
<https://www.rfc-editor.org/info/rfc5385>.
[SDMX] SDMX -- Statistical Data and Metadata Exchange,
<https://sdmx.org/>.
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9. Acknowledgments
Many thanks to Arofan Gregory, Dan Smith, and Wendy Thomas from the
DDI Alliance Technical Committee, and Peter Koch from DENIC (German
Network Information Center) for discussion and input that led to this
document.
The following software tools have been helpful in evaluating the ABNF
grammar and the regular expressions: an ABNF parser [ABNFPFE], a tool
that creates regular expressions from an ABNF grammar [ABNF2RS], and
a tool that generates random strings that match an ABNF grammar
[ABNFGEN].
This document was prepared using the Word template
2-Word-v2.0.template.dot [RFC5385].
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Appendix A. Example DNS Records
The examples use NAPTR [RFC3403] and SRV [RFC2782][RFC3958] records.
The values for the services and flags fields of the NAPTR records
will be determined by the DDI application ([RFC3403] section 9.).
A.1. Delegation of the URN Namespace "ddi"
Example records defined at a.iana-servers.net and other authoritative
name servers for the domain urn.arpa.
The empty flag indicates that the lookup is not terminal and the next
probe to DNS is for more NAPTR records where the new domain is
"registry.ddialliance.org".
; Delegation to name servers of ddialliance.org
; order pref flag service regexp replacement
ddi.urn.arpa.
IN NAPTR 100 10 "" "" "" registry.ddialliance.org.
A.2. Delegation of DDI Agencies
Example records defined at registry.ddialliance.org for ddi.urn.arpa.
The empty flag indicates that the lookup is not terminal and the next
probe to DNS is for more NAPTR records where the new domain is the
DNS server of the relevant DDI agency.
; Delegation to name servers of subdomains in ddi.urn.arpa, i.e.
; DDI agencies.
; order pref flag service regexp replacement
ddia1.us.ddi.urn.arpa.
IN NAPTR 100 10 "" "" "" dns.example1.edu.
ddia2.de.ddi.urn.arpa.
IN NAPTR 100 10 "" "" "" dns.example2.org.
ddia3.gb.ddi.urn.arpa.
IN NAPTR 100 10 "" "" "" dns.example3.ac.uk.
A.3. DDI Services
Example records defined at dns.example2.org for ddi.urn.arpa.
The "u" flag states that the rule is terminal and that the output is
a URI which contains the information needed to contact that DDI
service. The "s" flag states that the rule is terminal and that the
output of the rewrite will be a domain-name for which an SRV record
should be queried. See also [RFC4848] section 4.4.
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The service N2R returns one instance of the resource identified by
the given URN. That service is a repository of DDI resources
available at http://repos.example2.org/N2R/; possibly a REST-based
service. The service N2C returns a description of the resource
identified by the given URN. That service is a registry of DDI
resources available at registry-udp.example2.org port 10060.
U-NAPTR permits regular expressions of a form that does a complete
replacement of the matched string with a URI, expressed as a constant
string. With this limited form of regular expression ([RFC4848]
section 2.2.), applications using NAPTR need not implement full
regular expression parsers.
ddia2.de.ddi.urn.arpa.
; order pref flag
IN NAPTR 100 10 "u" "N2R+http" ( ; service
"!.*!http://repos.example2.org/N2R/!" ;regex
. ; replacement
)
IN NAPTR 100 10 "s" "N2C+udp" ( ; service
"" ; regex
_registry._udp.example2.org. ; replacement
)
; all subdomains in ddia2.de.ddi.urn.arpa.
*.ddia2.de.ddi.urn.arpa.
ddia2.de.ddi.urn.arpa.
; order pref flag
IN NAPTR 100 10 "u" "N2R+http" ( ; service
"!.*!http://repos.example2.org/N2R/!" ;regex
. ; replacement
)
IN NAPTR 100 10 "s" "N2C+udp" ( ; service
"" ; regex
_registry._udp.example2.org. ; replacement
)
;_service._protocol.name
; TTL class SRV priority weight port target
_registry._udp.example2.org
14400 IN SRV 0 0 10060 registry-udp.example2.org.
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Appendix B. Algorithm for DDI Service Discovery
The description is based on the Dynamic Delegation Discovery System
(DDDS) algorithm [RFC3402].
Application Unique String
The Application Unique String is a DDI URN.
First Well Known Rule
1. Extracting the characters between the second and third colon
(the agency identifier).
2. Normalizing case of that string.
3. Reversing the order of the substrings separated by dots.
4. Appending the string ".ddi.urn.arpa" to the end to get a domain
name.
Valid Databases
The DNS is specified as a DDDS Database for this application which
uses the NAPTR DNS resource records to contain the rewrite rules
for service discovery.
The DNS is queried for NAPTR records for the domain name which is
the output of the First Well Known Rule.
Expected Output
The expected output is the information necessary to connect to
authoritative server(s) (host, port, protocol, or URL) for an
application service within a given DDI agency. The result is a
list of terminal NAPTR records pointing to services available for
the relevant DDI agency.
The application selects the appropriate service and contacts the
service for the given URN.
The process can be optimized by an application cache for the NAPTR
records of already requested DDI agencies.
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Author's Address
Joachim Wackerow
c/o DDI Alliance, ICPSR, University of Michigan
PO Box 1248
Ann Arbor, MI 48106-1248
USA
Email: joachim.wackerow@posteo.de
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