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XBRL provides the ability to arrange the concepts within a taxonomy using networks of relationships. Real world usage of XBRL has uncovered two related shortcomings in the definition of these networks. Firstly, multiple independent networks maybe created, partitioned according to Extended Link Roles, but there is no standardised way to control the ordering between these networks. Secondly, within each network, there is no standardised mechanism to control the ordering between the concepts at the root.
This document provides requirements for solutions to these issues.
1 Introduction
2 Requirements
3 Local remedies
4 Current XBRL International specifications
A References
B Intellectual property status (non-normative)
C Acknowledgements (non-normative)
D Document history
E Errata corrections in this document
XBRL v2.1 [XBRL 2.1] supports the arrangement of concepts in a taxonomy into hierarchies through the use of relationships defined by XLink arcs. These hierarchies are used for a number of different purposes, including the presentation of the taxonomy concepts, and of facts in instance documents.
Recently a new presentation format has reached Recommendation status: the Table Linkbase [TABLELINKBASE]. This presentation specializes in rendering tables, also defined using XLink relationships.
The hierarchies are defined by relationships between pairs of concepts. These relationships are grouped according to their XLink Extended Link Role (ELR), allowing multiple, independent hierarchies to be defined. Concepts which have no incoming relationships within an ELR are conisdered to be the roots of that hierarchy.
The XBRL v2.1 Specification allows the relative ordering of relationships to be defined, but provides no mechanism to define the order of the root nodes within a hierarchy (there is no incoming relationship to which an order could be attached), and no mechanism to define ordering between ELRs.
Both of these issues have proven to be a practical a practical issue for the presentation of information in an XBRL taxonomy, and for the presentation of data in an instance document according to an XBRL taxonomy.
The solution should meet the following requirements:
Taxonomy authors around the world have taken initiatives to work around the omissions mentioned. For example:
The IFRS, US GAAP and UK GAAP taxonomies rely on software ordering ELRs according to alphanumerical ordering of the contents of the link:definition elements, and include a numeric code as the first part of the definition in order to control that ordering.
This approach requires software to sort according to the link:definition element, which is not required by the specification, but appears to have become de facto standard behaviour.
The Dutch SBR project uses a custom proprietary arcrole and resource element in a generic link linkbase. The resource element containing a decimal value to order ELRs.
The European Banking Authority (EBA) has a similar requirement to provide both
an ordering and a grouping of tables from a Table Linkbase. These
relationships have been captured through the introduction of a custom arc role
("group-table") used in a generic link for creating relationships between
abstract element declarations and table:table resources.
The Japanese EDINET taxonomy uses a "Table of Contents" ELR to provide an
overall structure to the taxonomy. The Table of Contents ELR contains nodes in
a specific substitution group (iod:identifierItem). These items
correspond to the root notes of other networks, and allows the Table of
Contents ELR to provide an ordered, hierarchical index of the other groups.
This approach requires software to be aware of the name or naming convention
for the special Table of Contents ELR, and of the linking provided by elements
in the iod:identifierItem substitution group.
There is no specification released by XBRL International that defines how ELRs or roots of networks be ordered. A widespread practice in XBRL-enabled software is to provide alphanumerical ordering based on the link:definition content or on the ELR URI (by omission of the link:definition node). For root parent relationships no such practice could be detected, although the issue of root-level ordering is typically avoided by introducing a single root node for each network.
The table grouping mechanism used by EBA is being generalised and standardised through the introduction of a generic parent-child arc role addition to the Link Role Registry [LRR STRUCTURE].
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This document could not have been written without the contributions of many people.
This appendix contains a list of the errata that have been incorporated into this document. This represents all those errata corrections that have been approved by the XBRL International Base Specification and Maintenance Working Group up to and including 10 December 2014. Hyperlinks to relevant e-mail threads may only be followed by those who have access to the relevant mailing lists. Access to internal XBRL mailing lists is restricted to members of XBRL International Inc.
No errata have been incorporated into this document.