Information on the version structure

With the June 2007 release for the OME XSD files we have move to a new versioning system. This composes of two parts, Major and Minor.

Major

The major part of a version is contained in the namespace of each schema. This consists of the month and year the schema was first released. The format for the new URI for the namespace will be

http://www.openmicroscopy.org/Schemas/[NameSpaceTitle]/[YearAsFourDigits]-[MonthAsTwoDigits]

This means the June 2007 major release for the OME schema uses the namespace

http://www.openmicroscopy.org/Schemas/OME/2007-06/

and that the schema file will be located at

http://www.openmicroscopy.org/Schemas/OME/2007-06/ome.xsd

Major versions will normally be released about twice a year. There will be a consultation period before each major release. Major releases may include breaking changes.

Minor

In the schema element of the XSD file there is a version attribute.

<xsd:schema xmlns="http://www.openmicroscopy.org/Schemas/OME/2007-06" 
	...
	version="1" 
	... >

This is used to record the minor version number of the schema. This starts at 1 and counts up in integers (1, 2, 3, etc.) with each minor version.

A new minor version is used for small non-breaking changes. If a change is more significant or would break application relying on the current schema then it must be a major version.

Minor versions will be released as needed.

Examples and consequences

The relation between a major and minor version has been set up as follows. Any file written by an application conforming to a major version will always continue to be valid under any minor version update to the schema. If microscope application X saves a file using the major June 2007 version of OME-XML then that file can be read by any application that understands either the June 2007 major version or the September 2007 minor version. The main consequence of this approach is that file readers have to be kept up to date or have to be written in a way that allows some flexibility.

An example of a minor change is the serial number in the manufacture specification. In the June 2007 major version a SerialNumber is required in ManafactSpec. It was decided to make this optional as it was not always available to a file writer. This is a minor change as if it is present or absent the new file can still validate.

An example of a major change is the moving of ImageRef from the SPW.xsd file to the ome.xsd file. This change had been proposed as it is envisaged that in the future ImageRef will be used outside the Screen/Plate/Well model so it belongs better in the same namespace as Image. As this means that any reference to SPW:ImageRef will have to become OME:ImageRef this would cause validation errors in files following the June 2007 schema. This is therefore not placed in the September 2007 minor release but held until the next major release.