The XBRL v2.1 specification, and most subsequent modules are defined in terms of the XML syntax of component documents, and do not explicitly define the semantic information that may be represented in and inferred from XBRL documents.
With the development of the Open Information Model 1.0 ("the OIM Report Model"), this has largely been addressed for the information represented by an XBRL Report.
It is proposed that a corresponding OIM Taxonomy Model be developed, to provide a syntax-independent definition of the information in an XBRL Taxonomy. Due to the breadth and variety of information defined in an XBRL Taxonomy, it is intended to tackle this in phases.
This document captures requirements for the first phase of an OIM Taxonomy Model. This is the first part of a phased approach, which is described in the OIM Taxonomy Model Implementation Plan Working Group Note.
This phase, referred to as Core Taxonomy Information (CTI), is intended to capture the taxonomy information needed by a processor implementing the OIM Report Model (see Section 1.5.2).
The primary goal of the Open Information Model Working Group is to ensure that XBRL remains relevant in the face of changing technologies by defining XBRL semantics in a syntax-independent manner. Specifically, this means:
The initial deliverables of the Core Taxonomy Information effort should be:
A specification of a limited-scope (Section 1.5.2), syntax-independent XBRL taxonomy model (“The CTI Model”). There is no requirement for this to be presented in any particular modelling language or format, provided that the result is clear and unambiguous.
A definition of the mapping from the existing XML-based syntax for XBRL taxonomies to the CTI Model.
A definition of a representation of an XBRL taxonomy that uses a non-XML-based syntax, and mappings between that syntax and the CTI Model.
It should be possible to convert a model-based representation of a taxonomy to the XML-based syntax and back again, resulting in an equivalent taxonomy model (sec Section 1.5.4). Note that the Core Taxonomy Information is only a subset of the information in an XBRL Taxonomy (see Section 1.5.2), and so round-tripping from XML to CTI model and back is a potentially lossy transformation.
Possible use cases for the deliverables are documented below.
A software developer may wish to develop an XBRL API that exposes a logical interface onto the data in an XBRL taxonomy. The CTI should enable as much syntactic detail as possible to be omitted from the API, and should make it possible to define an API that can be backed by alternative representations of XBRL (e.g. a database) without loss of functionality.
A consumer may wish to analyse XBRL data that has been published in xBRL-JSON format. Whilst the xBRL-JSON format is relatively simple, in certain cases correctly interpreting the data requires some taxonomy information. For example, it is necessary to know where fact and dimensions have QName values. In addition, as xBRL-JSON uses JSON strings for all fact and dimension values, correctly identifying numeric values requires some datatype information from the taxonomy.
A consumer of XBRL reports may wish to store reports in a database. The CTI should provide all the information required to losslessly store an OIM-compatible XBRL report in this way.
This use case shares many of the same requirements described in the preceding use case.
A software developer may wish to create a standalone document that combines all information from an OIM-compatible XBRL Report with the taxonomy information needed in order to correctly interpret the report data. This could be done by adding information at the permitted extensibility points of the xBRL-JSON format. The CTI should provide the information necessary for this conversion.
A user wishing to use XBRL for internal data processing needs may wish to create a minimal XBRL taxonomy in order to support this. For example, a user wishing to import CSV files into an OIM-compatible database may wish to define a taxonomy that contains the information necessary to perform this transformation without creating an XBRL taxonomy in XML syntax.
The CTI Model will unavoidably need to deal with technical detail as the starting point is the existing XBRL specifications which define XBRL in terms of a syntax rather than a logical model. As such, the model will need to reference the technical terms used in those documents, but, insofar as possible the constructs defined by the CTI Model should use terminology that will be meaningful to business users.
The CTI Model is intended to be the first step in a phase approach to modelling XBRL taxonomy information. The scope for the CTI deliverable is to model all taxonomy information that is required by a conformant processor implementing the Open Information Model, xBRL-CSV or xBRL-JSON specifications.
This means that features that are not required by such a processor, such as labels, references and inter-concept relationships, are out of scope for this phase.
Note that scope for the CTI Model is limited to conformant processors, as opposed to validating conformant processors. Any information that is only required by the latter is considered out of scope for the CTI Model. Most notably this means that full XML Schema datatype information, and most dimensional taxonomy information are not required.
The CTI Model must represent the implicit and explicit semantics currently captured in XBRL constructs that are in common use, and which are considered consistent with current XBRL best practice. It is not necessary for the Model to represent everything that is currently possible within XBRL’s XML syntax. It is acceptable for the CTI Model to omit certain XBRL features in order to achieve a clean, and portable model.
Note that the completeness requirements are independent of the scope requirements discussed above. Features that are omitted purely because they are out of scope for CTI will be included in future phases. Features that are omitted because they are deemed undesirable under this requirement will not be added in the future.
The CTI model should make it possible to determine if two taxonomies, possibly in two different syntaxes, communicate the same essential taxonomy information. Such comparison is limited to the scope of the CTI Model (see Section 1.5.2).
The CTI Model must capture semantics represented in XBRL taxonomies conforming to the following XBRL specifications, although as noted in Section 1.5.3, the model may exclude certain features from these specifications:
The CTI Model should, wherever possible, avoid modelling information that is inherently tied to XML syntax.
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