Best Practices on Extending CEBS Taxonomies

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Contribution dated 2007-08-22



This document describes the best practices on how to extend CEBS (Committee of European Banking Supervisors) taxonomies. The Committee of European Banking Supervisors (CEBS) has published XBRL taxonomies for the common reporting framework COREP (COmmon REPorting) for the new solvency ratio for credit institutions and investment firms and for the standardised financial reporting framework (FINREP) for credit institutions operating in the EU. These taxonomies are available on the website of the CEBS and on the project related websites and


This draft document is created by members of the XBRL network of the CEBS. Taxonomy Editor that are extending the CEBS taxonomies (COREP and/or FINREP)are invited to add comments, experiences and suggestions for improvement on how to extend these taxonomies in a practical way.

KS: As a first approach I've added chapter 7 of the COREP-FINREP documentation that deals with the extension of these taxonomies.

National Taxonomy Customisation COREP - FINREP

Extending the COREP and FINREP taxonomies is a similar process. In this document a COREP template is used for demonstration purposes; however, all the information provided below holds true for FINREP, as well. Please always take into account that FINREP modularisation is achieved by the use of extended link roles in only one primary taxonomy.

The COREP - FINREP taxonomies have been developed to be customisable – that means extensible and restrictive – by national supervisors. To facilitate the customisation of the taxonomies, the framework is as modular as possible and the structure of the taxonomies is similar to the construction of the CEBS COREP - FINREP templates. This means that the templates consist of measure and dimensions which are combined in a table. Therefore, the COREP taxonomy set consists of measure (primary dimension), dimension and template taxonomies.

In order to build extension taxonomies, the use of a taxonomy editing tool is recommended for their creation and maintenance. Links to useful XBRL tools for evaluation are available on the XBRL International website (

National extension structure

National extensions will use the COREP taxonomy as a base. Extensions are done by creating new taxonomies and importing the corresponding COREP taxonomies. So, the national extension taxonomy contains all the functionality of the underlying COREP taxonomy. Changes are made in the national extensions without amending the base COREP taxonomy. The national extension taxonomy can overwrite all the rules that are defined in the imported COREP taxonomy.

Categorisation of national taxonomy extensions

Customisations can be made on:

  • labels
  • references
  • the template structure
  • calculations.

The following chapters deal with these customisations and how these changes can be made easily for national extension taxonomies.

Creating extension taxonomy

All customisations start with the creation of a reference to the COREP taxonomy. This is done by building a new national taxonomy and importing the corresponding COREP taxonomy.

To customise a COREP template, a national taxonomy (i.e. “t-me-ISO country code-2006-MM-dd”) must be created. After setting up all the properties and the national namespace, the corresponding taxonomy of COREP should be imported.

After the import, the national extension taxonomy possesses the complete functionality of the underlying COREP taxonomy.

Customisation of labels

The labels of the COREP taxonomy contain the captions of the columns and rows of the templates and can be used to create reports. For example, the receipt of an XBRL instance document could be transformed into other formats as Adobe Pdf or Microsoft Excel to enable easier viewing of the data. In such documents, the labels are used to hide the technical element name. To generate reports in the national language, the English labels of the COREP taxonomy should be translated accordingly. This is done by adding a label linkbase to the extension taxonomy. In this way, each national supervisor can create a COREP dictionary to present reports in one or more languages.

Customisation of references

The COREP templates are based on the EU directive of Basel II. Therefore, references to this EU law will be added to the elements of the COREP taxonomies in version 1.0. If a national law exists that defines what must be reported, this law should be added as a reference because it overrides the rules of the EU directive.

Additional references are added by extending the national taxonomy with another reference linkbase.

A reference to the COREP base taxonomy can be removed by prohibiting the use of the reference arc.

The references build a good glossary because by following the reference of an element, the explanation of what has to be reported can be found in the EU directive or in the national law. No further descriptions are needed.

The COREP taxonomy uses a specific reference structure that accommodates the structure of the EU directive. The national law might have a different structure. To customise the reference structure, the basic reference linkbase should be extended by adding additional elements.

Customisation of the template structure

This sub-chapter briefly describes the following use cases and how they can be incorporated in the national extension taxonomy:

  • adding or removing columns and rows;
  • reordering the hierarchical structure of a template;
  • restricting cells from being reported (adding “grey cells”);
  • removing dimensions from a template;
  • providing choices among dimensions.

Adding or removing columns and rows

A national supervisor might decide that a column defined in the COREP structure is not needed for the reporting in his country, and so he wants to remove this column. Or else, he needs further information in the template and wants to add an additional column that is not defined in the COREP superset.

A column is removed by prohibiting the use of the arc between the measure and its superordinate parent element. An additional measure will be added in the national extension taxonomy and will be placed in the desired position in the presentation and definition linkbases by adjustment of the order attribute.

Reordering the hierarchical structure of a template

Restricting cells from being reported

Removing dimensions from a template

Providing choices among dimensions

Customisation of calculations

The calculation linkbase is used to define summations among measures in the measure taxonomies and to define aggregator-contributor relationships among dimension members of the corresponding dimension taxonomies.

The definition of calculations in the measure taxonomies enables the validation inside one context. Given that the measures of one row of a template are contained in one context because each row belongs to a different dimension, it is not possible to do the calculation across dimensions. In the future, the formula linkbase will support cross-context summations.

The national supervisors through the national taxonomies can extend and restrict the definitions of the calculation linkbases. It is done in the same way as before; by adding new element trees (adding calculations) or prohibiting arcs (removing calculations) in the linkbase.

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