The protocol is a CEN norm, developed originally as a technical standard with initial participation by France, Germany (Verband Deutscher Verkehrsunternehmen), Scandinavia, and the UK (RTIG) SIRI is based on the CEN Transmodel abstract model for public transport information, and comprises a general purpose model, and an XML schema for public transport information.
The information can be used for many different purposes, for example: CEN SIRI includes a number of optional capabilities.
A number of small enhancements were subsequently added as informal changes creating interim releases v1.1, v1.2, etc.
Two other CEN standards were developed that made use of the 'SIRI Common Protocol Framework' to define their own functional services; NeTEx (v1.0 published in 2014) and Open API for distributed journey planning (v 1.0 published in 2017).
This is backwards compatible with V1.0 and both formalises the adoption of the interim enhancements and adds a number of additional features.