This document is a review draft. Readers are invited to submit comments to the Taxonomy Architecture Guidance Task Force.


  • Paul Hulst, De Nederlandsche Bank
  • Ben Russell, CoreFiling


  • Erwin Kaats, Logius
  • Jochem Oosterlee, Visma Connect
  • Revathy Ramanan, XBRL International Inc.
  • Joel Vicente, CoreFiling
  • Paul Warren, XBRL International Inc.

Table of Contents

1 Introduction

This guidance explains how reusing an existing taxonomy can be beneficial to taxonomy authors and users. It explains what is meant by reuse and covers business and technical considerations that can be considered best practice. The guidance is primarily provided for taxonomy architects incorporating pre-existing taxonomy(s) in a new, distinct taxonomy.

2 What is reuse?

Reuse means importing components from an existing taxonomy into your own. Reuse may cover any part of a taxonomy, including taxonomy elements, labels, references, formula functions, data types or a presentation tree. It is an alternative to replicating or redoing modelling when an acceptable solution has already been developed.

In this document, we consider the case where the new taxonomy includes additional content as well as other taxonomies. We also assume the normal case where any taxonomies being reused are published separately and by a different owner.

Other methods of reuse, such as those below, are not considered within this document:

  • Only adding new labels (e.g. in another language).
  • Other repackaging of a taxonomy with no additional elements.

3 When should you reuse?

Usually, the decision to reuse is made by taxonomy architects and authors during the initial stages of taxonomy development. If they can identify an existing, publicly available taxonomy that contains components that meet their requirements, then it is recommended that they make use of these pre-existing components in preference to writing their own.

Reuse is recommended when it is beneficial to guarantee consistency with a pre-existing taxonomy. The alternative is to redefine similar items, which requires the taxonomy users to determine if the concepts are exactly the same.

Good examples of reuse are given below:

  • The European Securities and Markets Authority (ESMA) requires public listed companies to provide IFRS financial statements in iXBRL under the European Single Electronic Filing (ESEF) system. The ESEF taxonomy imports the IFRS taxonomy published by the IFRS Foundation to reuse their concepts, thus guaranteeing to users that these concepts are the same.

  • The European Insurance and Pensions Authority’s (EIOPA) Solvency II reporting requirement, and the European Banking Authority’s (EBA) CRD IV reporting requirement are built on a common technical framework. Taxonomies for both of these import the EuroFiling taxonomy in order to reuse the interval arithmetic calculation logic and data point modelling concepts. This saves time and effort and ensures calculation consistency amongst all taxonomies that use this logic.

A good example of a taxonomy specifically designed for reuse is the LEI taxonomy published by XBRL International, which provides a standard method for incorporating Legal Entity Identifiers (LEIs) and related functions into XBRL reports.

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