Well-formed link definition, 2006
Geoff Shuetrim (geoff@galexy.net) Galexy Pty. Limited.
This document is a public working draft. All comments are welcome and should be emailed directly to the author.
This document is copyright Galexy Pty. Limited.
This document is non-normative. It simply clarifies the constraints on extended links that are well formed in the sense that they comply with the XBRL 2.1 specification.
Throughout this document, namespace prefixes are used for elements and attributes in place of the full namespace to which they correspond. The mappings from namespace prefixes to actual namespaces, as used in this document, are set out below.
|
Namespace prefix |
Namespace |
|---|---|
|
xbrli |
http://www.xbrl.org/2003/instance |
|
xl |
http://www.xbrl.org/2003/XLink |
|
link |
http://www.xbrl.org/2003/linkbase |
|
xlink |
http://www.w3.org/1999/xlink |
|
xml |
http://www.w3.org/XML/1998/namespace |
Where this document refers to an XML schema, it is referring to an XML document that contains a declaration of a schema that is compliant with XML Schema.
This document defines the notion of a well-formed extended link, for use with modular extensions of XBRL. This definition is targeted at editors of modular extensions to XBRL, helping them to move beyond the unnecessary limitations of the explicit extended links in the core XBRL specification.
The definition of well-formed links in this document fully conforms to the XBRL specification [1]. All links that are explicitly described in the XBRL 2.1 specification are well-formed based on the definition in this document. Moreover, all well-formed links are valid links, based on the XBRL specification.
This means that software complying with the XBRL specification can already handle all well-formed links conforming to the definition set out in this definition. Specifically, such software can form a Discoverable Taxonomy set (DTS) and base sets of arcs in that DTS, where the DTS includes well-formed links. However, such software will not necessarily be able to respond to the information expressed by the relationships and resources in a well-formed link. To do so, the software would also have to be in conformance with the specification that describes the nature of the information that can be expressed by those specific types of relationships and resources.
An important conclusions in this document include:
Locators in well-formed links MAY reference XML fragments in XML schemas that are not XBRL concept declarations.
A well-formed link MAY contain several different XLink resource elements, where those elements are differentiated by their element names.
These possibilities
By recognising these implications, the ability to document XBRL information using new kinds of extended links is significantly enhanced. Obvious possibilities include:
documenting link:roleType and link:arcroleType elements in multiple languages;
labelling reference part declarations; and
documenting the hierarchical relationships between reference part declarations.
A well-formed link is an XLink extended link satisfying all of the conditions set out in this document.
Well-formed links MUST be valid extended links as defined in the XLink specification.
Well-formed links MUST be valid XBRL extended links.
This means that:
they MUST conform to the XML schema constraints implied by the xl:extendedType;
they MUST have a non-empty xlink:role attribute on the extended link element; and
they MUST have an xlink:type attribute with a value of “extended”.
Note that the XML Schema content model for a well-formed link does not have to explicitly enumerate the specific arcs or resources that are permitted within it.
Locators in well-formed links are referred to as well-formed locators.
Well-formed locators MUST be valid XLink locators.
Well-formed locators MUST be valid XBRL locators.
This means that:
they must be link:loc elements;
they MUST have an xlink:type attribute with a value of “locator”.
Note that it does not impose any restrictions on the nature of the resources identified by the xlink:href attribute on a well-formed locator.
To conform with the the XBRL rules of DTS discovery, all well-formed locators MUST reference XML fragments that are themselves in XML schemas or linkbases that then qualify for inclusion in the DTS. This rules out locators that reference non-XML resources. It also rules out locators that reference XML fragments that are not nested within a linkbase or an XML schema.
Note that locators referencing any XML fragment in an XML schema imply that that XML schema is part of the DTS. This implies that well-formed links MAY associate XLink resources with fragments in XML schemas other than XBRL concept declarations.
Arcs in well-formed links are referred to as well-formed arcs.
Well-formed arcs MUST be valid XLink arcs.
Well-formed arcs MUST be valid XBRL arcs.
This means that:
they MUST conform to the XML schema constraints implied by the xl:arcType.
they MUST have an xlink:type attribute with a value of “arc”.
Resources in well-formed links are referred to as well-formed resources.
Well-formed resources MUST be valid XLink resources.
Well-formed resources MUST be valid XBRL resources.
This means that:
they MUST conform to the XML schema constraints implied by the xl:resourceType.
they MUST have an xlink:type attribute with a value of “resource”.
Note that the xl:resourceType type definition implies that a well-formed link MAY contain more than one type of XLink resource element, where such types of resource elements are distinguished by their element names.
All well-formed links in a linkbase referenced by a link:linkbaseRef will be included in the DTS and be analysed as part of the DTS discovery process.
All well-formed links that are embedded in a schema that is itself part of a DTS, will also be included in the DTS and be analysed as part of the DTS discovery process.
Note, however, that the definition of the DTS is limited to the set of schemas and linkbases that are discoverable using the XBRL rules of discovery. Resources that are neither linkbases, nor schemas MAY be discovered by a well-formed locator, even though they are not formally part of the DTS.
Based on the definition provided in this document, all arcs in well-formed links can be grouped into base sets of arcs, as defined in the XBRL specification.