Internet DRAFT - draft-urn-ddi
draft-urn-ddi
Network Working Group Joachim Wackerow
Internet Draft DDI Alliance
Intended status: Informational August 13, 2023
Expires: February 2024
A Uniform Resource Name (URN) Namespace for the
Data Documentation Initiative (DDI)
draft-urn-ddi-06.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/).
The DDI Alliance is not affiliated with the Internet Engineering
Task Force (IETF) or Internet Society (ISOC); and as an
independent submission, it does not have IETF community consensus.
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
other groups may also distribute working documents as Internet-
Drafts. The list of current Internet-Drafts is at
http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
This document is published for informational purposes. It is an
independent submission. It is not an Internet Standard and does
not have rough consensus of the IETF community.
This Internet-Draft will expire in February 2024.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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respect to this document.
Code Components extracted from this document must include
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Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................4
3. Specification..................................................5
3.1. Declaration of Syntactic Structure...........................5
3.1.1. Description................................................5
3.1.2. ABNF Grammar...............................................6
3.1.3. Regular Expression.........................................8
3.1.4. Examples of DDI URNs.......................................9
3.2. Relevant Ancillary Documentation.............................9
3.3. Identifier Uniqueness Considerations........................10
3.4. Identifier Persistence Considerations.......................10
3.5. Process of Identifier Assignment............................10
3.6. Process for Identifier Resolution...........................10
3.7. Rules for Lexical Equivalence...............................11
3.8. Conformance with URN Syntax.................................12
3.9. Validation Mechanism........................................12
3.10. Scope......................................................12
4. Namespace Considerations......................................12
4.1. URN Assignment Procedures...................................12
4.2. URN Resolution/Delegation...................................12
4.3. Type of Resources to be Identified..........................12
4.4. Type of Services............................................12
5. Community Considerations......................................13
5.1. Open Assignment and Use of Identifiers......................13
5.2. Open Operation of Resolution Servers........................13
5.3. Creation of Software for Service Discovery..................13
6. IANA Considerations...........................................14
7. Security Considerations.......................................14
8. References....................................................14
8.1. Normative References........................................14
8.2. Informative References......................................16
9. Acknowledgments...............................................19
Appendix A. Example DNS Records..................................20
A.1. Delegation of the URN Namespace "ddi".......................20
A.2. Delegation of DDI Agencies..................................20
A.3. DDI Services................................................20
Appendix B. Algorithm for DDI Service Discovery..................22
B.1. Application Unique String...................................22
B.2. First Well Known Rule.......................................22
B.3. Valid Databases.............................................22
B.4. Expected Output.............................................22
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].
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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. This memo
describing the ddi URN is an informational specification. It is
not a standard and is not the product of the IETF.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
appear in all capitals, as shown here.
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.
"DDI agency": An organization which maintains DDI resources.
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"DDI Alliance": Alliance for the Data Documentation Initiative
(DDI).
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. Declaration of Syntactic Structure
3.1.1. 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].
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
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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.
3.1.2. 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 = "!" / "$" / "&" / "'" / "(" / ")" /
"*" / "+" / "," / ";" / "="
separator = ":"
sub-separator = "."
; ALPHA and DIGIT are actually defined in the ABNF
specification.
; They are declared here for convenience purposes.
ALPHA = %x41-5A / ; uppercase letters
%x61-7A ; lowercase letters
DIGIT = %x30-39 ; digits
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3.1.3. Regular Expression
The used syntax is the XML Schema flavor which can be easily used
in other flavors. These regular expressions implicitly anchor at
the head and tail. The following regular expression syntax uses
components (component names indicated by angle brackets, i.e.
<component>) and is written in free-spacing mode for easier
reading (the XML Schema flavor does not support that). Please note
that use of multiple quantifiers in regular expressions can result
in false outcomes due to so-called greediness. Therefore, there
are separate regular expressions for the length restriction and
other purposes for the components agency-identifier and dns-label.
ddi-urn := [Uu][Rr][Nn] : [Dd][Dd][Ii] :
<agency-identifier> :
<resource-identifier> :
<version-identifier>
agency-identifier := <top-level-domain> \.
<ddi-authority-id>
(\. <ddi-sub-authority-id>)*
agency-identifier := .{1,255}
top-level-domain := <dns-label>
ddi-authority-id := <dns-label>
ddi-sub-authority-id := <dns-label>
dns-label := [A-Za-z0-9]([-A-Za-z0-9]*[A-Za-z0-9])?
dns-label := .{1,63}
resource-identifier := <restricted-string>
(/ <restricted-string>)*
version-identifier := <restricted-string>
(/ <restricted-string>)*
restricted-string := [A-Za-z0-9-._~!$&'()*+,;=@]+
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3.1.4. 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].
3.2. 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.
o Regarding size limits, see [RFC1123] section 2.1 and [RFC1035]
section 2.3.4.
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3.3. 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.
3.4. 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.
3.5. 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.
3.6. 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
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".
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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.
3.7. 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>:
is case-insensitive for matches. The remainder of the identifier
MUST be considered case-sensitive.
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3.8. 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.
3.9. Validation Mechanism
The DDI Alliance will promote development of software for
validation purposes.
3.10. 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 section 3.5, 'Process of Identifier Assignment'.
4.2. URN Resolution/Delegation
See section 3.6, '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 [RFC2483].
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o DDI repository
o I2R (URI to Resource): given a DDI URN return one instance
of the resource identified by that URN.
o DDI registry
o I2C (URI to URC, Uniform Resource Characteristics are
descriptions of resources): given a DDI URN return a
description or a summary of that resource.
o DDI URN resolution
o I2L (URI to URL): given a DDI URN return one URL that
identifies a location where the identified DDI resource can
be found.
o I2Ls (URI to URLs): 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
IANA is requested to update the "ddi" entry in the Universal
Resource Names registry to reference this specification.
The registration for "ddi" in the "URN.ARPA" zone is approved.
Requests for the domain ddi.urn.arpa will be delegated to the name
servers of the DDI Alliance.
7. Security Considerations
URN:DDI identifiers are assigned to resources that are public
information, and therefore resolving these identifiers has low
security profile.
Registration of DDI agencies is approved by the DDI Alliance.
Assignment and resolution of URN:DDI identifiers are controlled by
the DDI Alliance and approved DDI agencies. The DDI Alliance SHALL
have in place control mechanisms in order to make sure that DDI
Agency applications from malicious 3rd parties will not be
accepted. URN:DDI resolvers will be protected against
eavesdropping and attacks with appropriate tools.
This document introduces no additional technical 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. DNS over HTTPS (DoH) [RFC8484] could be used
to increase security by preventing eavesdropping and manipulation
of DNS data by man-in-the-middle attacks. The HTTPS protocol
encrypts the data between the DoH client and the DoH-based DNS
resolver.
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>.
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[DDIID] DDI Lifecycle (3.3) Technical Guide, Identification,
<https://ddi-lifecycle-technical-
guide.readthedocs.io/en/latest/General%20Structures/Iden
tification.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>.
[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>.
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[RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", RFC 8141, April 2017,
<https://www.rfc-editor.org/info/rfc8141>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", RFC 8174, May 2017, <https://www.rfc-
editor.org/info/rfc8174>.
[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/>.
[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/RepresentedVaria
ble.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/>.
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[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/>.
[IS19115] ISO 19115, Geographic information -- Metadata,
<https://www.iso.org/standard/26020.html>.
[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>.
[RFC2843] Mealling, M., Daniel, R., "URI Resolution Services
Necessary for URN Resolution", RFC 2483, January 1999,
<https://www.rfc-editor.org/info/rfc2483>.
[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>.
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[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>.
[RFC8484] Hoffman, P., McManus, P., "DNS Queries over HTTPS
(DoH)", RFC 8484, October 2018, <https://www.rfc-
editor.org/rfc/rfc8484>.
[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.).
For a description of the packet format of NAPTR, see [RFC3403]
section 4.1.
A.1. Delegation of the URN Namespace "ddi"
Example records below are 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 "dns.ddialliance.org".
; Delegation to name servers of ddialliance.org
; order pref flag service regexp replacement
ddi.urn.arpa.
IN NAPTR 100 10 "" "" "" dns.ddialliance.org.
A.2. Delegation of DDI Agencies
Example records below are defined at dns.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 below are 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
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the output of the rewrite will be a domain-name for which an SRV
record SHOULD be queried. See also [RFC4848] section 4.4.
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 targetreplac
_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].
The application selects the appropriate service from the output
described below 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.
B.1. Application Unique String
The Application Unique String is a DDI URN.
B.2. 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.
B.3. 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.
B.4. 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.
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Author's Address
Joachim Wackerow
c/o The Data Documentation Initiative Alliance (DDI Alliance)
ICPSR, University of Michigan
PO Box 1248
Ann Arbor, MI 48106-1248
USA
Email: joachim.wackerow@posteo.de, secretariat@ddialliance.org
Website: ddialliance.org
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