Universal Data Identifiers

Abstract

This document describes Universal Data Identifiers, which are in essence a set of conventions on the use of existing standards to reference data objects across a range of heterogeneous data sources and using an extensible set of network protocols. These data sources, called Contexts, and their contents, called Resources and their associated Attributes can be globally resolvable thus enabling objects to be interconnected to form a Global Graph.

Note

This document describes the syntax of UDIs. A separate document describes the URI resolution process. See UDI Resolution (Sabadello, M., Trevithick, P., and D. Reed, “UDI Resolution,” .) [udi‑resolution] .

Copyright

Copyright (c) 2008 Parity Communications, Inc. All rights reserved. This document is made available under the terms of the Eclipse Public License v1.0 as well as under the terms of the GNU General Public License v2.0. These licenses are available at: http://www.eclipse.org/legal/epl-v10.html, http://www.gnu.org/licenses/gpl-2.0.html

Table of Contents

1.  Terminology
2.  Introduction
3.  Context UDIs
    3.1.  Definition
    3.2.  Types of Context UDIs
    3.3.  Examples
4.  Resource UDIs
    4.1.  Definition
    4.2.  Types of Resource UDIs
    4.3.  Examples
5.  Attribute UDIs
    5.1.  Definition
    5.2.  Types of Attribute UDIs
    5.3.  Examples
6.  External ABNF rules
7.  Security Considerations
8.  References
    8.1.  Normative References
    8.2.  Non-Normative References
Appendix A.  Links
§  Authors' Addresses

1.  Terminology

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 RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119] .

2.  Introduction

Universal Data Identifiers (UDIs) are pointers designed to address any data object available on the Internet from a range of heterogeneous data sources. These data objects as well as connections between them constitute a Global Graph.

UDIs include Context UDIs, Resource UDIs and Attribute UDIs.

A Context UDI is an absolute identifier that points to a Context in a Global Graph. A Context is a set of Resources. A Context could be an LDAP directory, a relational database, an RDF document, the Facebook social network, an XDI endpoint, etc.

A Resource UDI is an absolute or relative identifier that points to a Resource in a Context in a Global Graph. Resources can have Attributes.

An Attribute UDI is an absolute or relative identifier that points to an Attribute of a Resource in a Context in a Global Graph.

In order to obtain the information needed to fully identify a Context, a Resource or an Attribute a UDI points to, UDI Resolution is performed.

For more information on how to perform resolution on a UDI, see UDI Resolution (Sabadello, M., Trevithick, P., and D. Reed, “UDI Resolution,” .) [udi‑resolution] .

3.  Context UDIs

3.1.  Definition

• A Context UDI is an absolute identifier that points to a Context in a Global Graph.
• Two different Context UDIs may refer to the same Context .
• A Context UDI provides all information necessary to completely identify the Context it points to. In order to obtain this information, UDI Resolution is performed.

3.2.  Types of Context UDIs

A Context UDI can be in one of the following forms:

1. XRI form
2. URI form without a fragment

A Context UDI in XRI form can be any XRI that can be resolved with XRI Resolution 2.0 (Wachob, G., Reed, D., Chasen, L., Tan, W., and S. Churchill, “Extensible Resource Identifier (XRI) Resolution Version 2.0,” .) [xri‑resolution‑V2.0‑cd‑03] .

A Context UDI in XRI form must conform to the following ABNF:

context-udi-xri       = context-udi-qxri / context-udi-hxri
context-udi-qxri      = ( [ "xri://" ] context-udi-qxri2 ) / ( [ "xri:" ] context-udi-qxri3 )
context-udi-qxri2     = xri2-authority [ "/($context)" *xri2-subseg ]
context-udi-qxri3     = xri3-authority [ "/$context" *xri3-subseg ]
context-udi-hxri      = hxri-proxy "/" (context-udi-qxri2 / context-udi-qxri3 )
hxri-proxy            = ( "http://" / "https://" ) hxri-proxy-reg-name
hxri-proxy-reg-name   = "xri." ireg-name

A Context UDI in URI form without a fragment is considered to be an XRDS URI, as defined in section 6 of XRI Resolution 2.0 (Wachob, G., Reed, D., Chasen, L., Tan, W., and S. Churchill, “Extensible Resource Identifier (XRI) Resolution Version 2.0,” .) [xri‑resolution‑V2.0‑cd‑03] .

A Context UDI in URI form without a fragment must conform to the following ABNF:

context-udi-uri       = context-udi-uri-file / context-udi-uri-http
context-udi-uri-file  = [ "file://" ] ipath-abempty descriptor-ext
context-udi-uri-http  = ( "http://" / "https://" ) iauthority ipath-abempty [ descriptor-ext ] [ "?" iquery ]
descriptor-ext        = ".xrds" / ".xdi"

3.3.  Examples

Note: Examples marked with (*) are described in greater detail in UDI Resolution (Sabadello, M., Trevithick, P., and D. Reed, “UDI Resolution,” .) [udi‑resolution] .

Context UDIs: XRI form (XRI Syntax 2.0)

Context UDIs: XRI form (XRI Syntax 3.0)

Context UDIs: URI form without a fragment

4.  Resource UDIs

4.1.  Definition

• A Resource UDI is an absolute or relative identifier that points to a Resource in a Context in a Global Graph. Resources can have Attributes .
• An absolute Resource UDI may include a Context UDI within itself to absolutely identify the Context which the Resource belongs to.
• An absolute Resource UDI provides all information necessary to completely identify the Resource it points to. In order to obtain this information, UDI Resolution is performed.
• A relative Resource UDI identifies a Resource in a Context that is known a priori. A relative Resource UDI can be any string that makes sense for the particular Context .

4.2.  Types of Resource UDIs

Absolute Resource UDIs can be in one of the following forms:

1. XRI form
2. URI form without a fragment
3. URI form with a fragment

An absolute Resource UDI in XRI form includes within itself a Context UDI in XRI form, which points to the Context the Resource belongs to. It must include a double-slash (//), which separates the Context UDI from the relative Resource UDI.

An absolute Resource UDI in XRI form must conform to the following ABNF:

resource-udi-xri      = resource-udi-xri2 / resource-udi-xri3
resource-udi-xri2     = context-udi-xri2 "//" xri2-segment
resource-udi-xri3     = context-udi-xri3 "//" xri3-segment

An absolute Resource UDI in URI form without a fragment is considered to be either a Semantic Web Linked Data "303" Cool URI, as described in section 4.1 of Cool URIs for the Semantic Web (Sauermann, L. and R. Cyganiak, “Cool URIs for the Semantic Web,” .) [CoolURIs] , or an XRDS URI, as described in section 6 of XRI Resolution 2.0 (Wachob, G., Reed, D., Chasen, L., Tan, W., and S. Churchill, “Extensible Resource Identifier (XRI) Resolution Version 2.0,” .) [xri‑resolution‑V2.0‑cd‑03] .

An absolute Resource UDI in URI form without a fragment must conform to the following ABNF:

resource-udi-uri-without-fragment      = [ scheme ] iauthority ipath-abempty [ "?" iquery ]

An absolute Resource UDI in URI form with a fragment is considered to be either a Semantic Web Linked Data "Hash" Cool URI, as described in section 4.2 of Cool URIs for the Semantic Web (Sauermann, L. and R. Cyganiak, “Cool URIs for the Semantic Web,” .) [CoolURIs] , or an XRDS URI, as described in section 6 of XRI Resolution 2.0 (Wachob, G., Reed, D., Chasen, L., Tan, W., and S. Churchill, “Extensible Resource Identifier (XRI) Resolution Version 2.0,” .) [xri‑resolution‑V2.0‑cd‑03] .

An absolute Resource UDI in URI form with a fragment must conform to the following ABNF:

resource-udi-uri-with-fragment      = [ scheme ] iauthority ipath-abempty [ "?" iquery ] "#" ifragment

4.3.  Examples

Note: Examples marked with (*) are described in greater detail in UDI Resolution (Sabadello, M., Trevithick, P., and D. Reed, “UDI Resolution,” .) [udi‑resolution] .

Resource UDIs: XRI form (XRI Syntax 2.0)

Resource UDIs: XRI form (XRI Syntax 3.0)

Resource UDIs: URI Form without a fragment (Semantic Web Linked Data "303" Cool URI)

Resource UDIs: URI Form without a fragment (XRDS URI)

Resource UDIs: URI Form with a fragment (Semantic Web Linked Data "Hash" Cool URI)

Resource UDIs: URI Form with a fragment (XRDS URI)

5.  Attribute UDIs

5.1.  Definition

• An Attribute UDI is an absolute or relative identifier that points to an Attribute of a Resource in a Context in a Global Graph .
• An absolute Attribute UDI may include a Resource UDI within itself to absolutely identify the Resource which the Attribute belongs to.
• An absolute Attribute UDI provides all information needed to identify the Attribute it points to. In order to obtain this information, UDI Resolution is performed.
• A relative Attribute UDI identifies an Attribute of a Resource that is known a priori. A relative Attribute UDI can be any string that makes sense for the particular Resource .

5.2.  Types of Attribute UDIs

Attribute UDIs can be in one of the following forms:

1. XRI form

An absolute Attribute UDI in XRI form includes within itself a Resource UDI in XRI form, which points to the Resource the Attribute belongs to. The absolute Attribute UDI in XRI form must include a double slash (//), which separates the Context UDI from the relative Resource UDI, as well as a single slash (/), which separates the relative Resource UDI from the relative Attribute UDI.

An absolute Attribute UDI in XRI form must conform to the following ABNF:

attribute-udi-xri      = attribute-udi-xri2 / attribute-udi-xri3
attribute-udi-xri2     = resource-udi-xri2 "/" xri2-segment
attribute-udi-xri3     = resource-udi-xri3 "/" xri3-segment

5.3.  Examples

Note: Examples marked with (*) are described in greater detail in UDI Resolution (Sabadello, M., Trevithick, P., and D. Reed, “UDI Resolution,” .) [udi‑resolution] .

Attribute UDIs: XRI form (XRI Syntax 2.0)

Attribute UDIs: XRI form (XRI Syntax 3.0)

6.  External ABNF rules

All ABNF rules not defined in this document are defined in the ABNF for XRI Syntax 2.0 (Reed, D., “ABNF for XRI Syntax 2.0,” .) [Xri2dot0Abnf] (which includes the IRI ABNF from RFC 3987 (Duerst, M. and M. Suignard, “Internationalized Resource Identifiers (IRIs),” January 2005.) [RFC3987] ) except:

• xri2-authority and xri2-subseg are the xri-authority and xri-subset rules defined in the ABNF for XRI Syntax 2.0 (Reed, D., “ABNF for XRI Syntax 2.0,” .) [Xri2dot0Abnf] .
• xri3-authority and xri3-subseg are the xri-authority and xri-subset rules defined in the Proposed ABNF for XRI Syntax 3.0 (Reed, D., “Proposed ABNF for XRI Syntax 3.0,” .) [XriThreeSyntaxAbnf] .

7.  Security Considerations

8.  References

8.1. Normative References

8.2. Non-Normative References

Appendix A.  Links

Higgins Project

Authors' Addresses