The use of XML has been mandated by the e-Government Interoperability Framework (e-GIF) programme as the standard to be used for messaging by government organisations and has accordingly been adopted by the NHS.

For the submission of Commissioning Data Set data to the Secondary Uses Service, XML based messaging has been developed replacing all previously published Commissioning Data Set Message formats.

The CDS-XML Message Schema is supported and applied in the Secondary Uses Service front-end software service (the XML Transfer Service - XTS) to enforce a nationally agreed data specification and thus help protect the data quality and integrity of the data submitted to and stored within the Secondary Uses Service.

It should be noted that after accepting the schema instance data, the Secondary Uses Service then applies further logical data validations and may identify and report further data conditions.

For the most part, the schema applies the data specifications as authorised by the NHS and documented in the NHS Data Model and Dictionary. However, as the NHS Data Model and Dictionary is updated on a continuous time basis and schemas are usually less dynamic and by nature updated on a longer time cycle, there may be subtle differences in the data specifications applied in the schema.

This variation often applies where a schema may contain historic data element values and the NHS Data Model and Dictionary may have been updated with a revised set of values since the schema was last released.

Another variation is where a schema deliberately retains historic values as well as supporting the new values in order to enable NHS users to be able to process historic data.

Schema Standards
The overall standards applied and supported by the schema are:

• W3C schema standards
• e-Government Interoperability Framework (e-GIF)
• e-GOV Best Practice guidelines for XML Schema
• The NHS Data Model and Dictionary

Schema Naming Conventions
These are in CamelCase as accepted best practice. Wherever possible, schema data item names are compliant (or intuitively identifiable) with the NHS Data Model and Dictionary naming conventions.

Schema Documentation
Schema documentation usually consists of several related publications:

• Information Standards Notices (ISN)  issued for NHS business, process and definition changes; these will usually include the Data Sets, Data Element definitions etc.
• Information Standards Notices issued to authorise the CDS-XML Schema itself
• The CDS-XML Schema Release Notice which provides a technical overview of the release (in MS WORD)
• The XMLSPY©) generated Schema Documentation which is a large collection of HTML files.

• The Standard Data Elements
• The Standard Data Structures
• All sub-component schemas for CDS TYPES including the Commissioning Data Set Headers and Trailers