Service Interface for Real Time Information

The Standard Interface for Real-time Information or SIRI is an XML protocol to allow distributed computers to exchange real-time information about public transport services and vehicles. 
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.
A SIRI White Paper is available for further information on the protocol.
Scope.
CEN SIRI allows pairs of server computers to exchange structured real-time information about schedules, vehicles, and connections, together with informational messages related to the operation of the services. The information can be used for many different purposes, for example:
CEN SIRI includes a number of optional capabilities.
Different countries may specify a country profile of the subset of SIRI capabilities that they wish to adopt.
Architecture.
The CEN SIRI standard has two distinct components:
CEN SIRI Functional Services.
SIRI V1.0 defined eight functional services;
Two further functional services have been added as part of the CEN SIRI specification;
Other CEN Standards that use the SIRI Common Protocol Framework.
The "CEN SIRI Common Protocol Framework" can be used by other standards to define their own Functional Services. Two CEN standards that do this are;
Current version & Documentation.
Version 2.0 of SIRI , representing the CEN documents as published, is currently available as a set of XSD files packaged as a zip file .
SIRI is maintained under a maintenance regime, with version control managed by a working group of the CEN TC/278 Working Group 3 . Later versions of the schema are available at the same site, together with change notes.
History.
The CEN SIRI standard was developed from European national standards for real-time data exchange, in particular the German VDV 453 standard, between 2000 and 2005, and included eight functional services. V1.0 became a CEN Technical Standard in 2006 and a full CEN standard in 2009. 
Two additional functional services were added later Situation Exchange (SX) (Technical Standard 2009, Standard 2016) and Facility Monitoring (FM) (2011).
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).
Version 2.0 of CEN-SIRI was developed between adopted in 2015. This is backwards compatible with V1.0 and both formalises the adoption of the interim enhancements and adds a number of additional features.
An important new addition in SIRI v2.0 was the description of a uniform transform for rendering CEN-SIRI messages into a flat format that can be used in simple http requests without an XML rendering.
Example of sites using SIRI.
Different SIRI implementations are used in a number of sites globally