3.2 Introduction

This chapter mainly deals with two topics concerning FDT version interoperability:
1. Persistence
New versions of FDT components (Frame Applications and DTMs) must be able to load project data of older versions.

2. Component Interoperability
Components of different FDT versions must interoperate properly. DTMs of newer FDT versions must run in older Frame Applications and vice versa. Communication must work even if FDT versions of Device-DTMs and Communication-DTMs differ.

A limiting condition for future FDT-enhancements is to ensure maximum compatibility of different FDT versions. This results in a maximum interoperability of FDT components originally designed for different FDT versions.
FDT takes care about version interoperability on two different levels:

1. Specification Level
The FDT specification targets full compatibility of different specification releases (e.g. schemas of the newer releases are compatible with older versions). Properly designed FDT components will achieve compatibility without extra implementations.

2. Implementation Level
FDT provides test tools to examine the FDT compliance of FDT components. Although mentioned here, this is not in the scope of this document.

The FDT version is composed by a major, a minor, a release and a build number (e.g. 1.2.0.3 where 1 is the major , 2 is the minor number, 0 the release and 3 the build number). Compatibility is defined slightly different with respect to the major number:

• Compatibility between FDT components with the same FDT major version number is assured by the specification.
• Compatibility between FDT components with different FDT minor, release and build version numbers can be achieved by extra code paths. FDT will provide needed information and mechanisms to support full compatibility at this level. The minor or release number is increased if new functionality, dependent of it’s appropriate importance, is added to the FDT specification. The build number is increased if a bugfix within the specification or the type library is necessary.