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Referenced Specification(s)

FCG TS61804-4 EDD Interpretation


Especially in offline use cases, users wish to have dependent values recalculated, if they change an engineering unit. FDI and EDDL specifications allow different host behaviours when it comes to unit conversion. If the user changes an engineering unit, an FDI host may recalculate the values depending on that engineering unit. But this behaviour is not mandatory for FDI hosts. On the other hand, FDI Package developers may implement unit conversion in the EDD. Currently, there is neither a way for a host to detect if unit conversion is implemented in the FDI Package. Also, an FDI Package cannot detect if a host performs unit conversion. If unit conversion is done by the FDI host and the FDI Package, this leads to unexpected results.


How can an FDI Host adopt its behaviour concerning unit conversion to the FDI Package?


Package Feature Table

This interpretation resolution introduces a feature table as new mandatory part of an FDI Package. The feature table provides information about the features provided by the FDI Package and the features requested by the FDI Package from the FDI Host. This information is used by the FDI Server to interpret the contents of the FDI Package in the correct way. The features and thus the possible entries of the feature table are specified in the following subclauses.

If an FDI Package provides a specific feature, the respective feature shall be listed in the feature table. If a feature is not listed in the feature table, it is assumed that the feature is not provided by the FDI Package.

If an FDI Package requests a specific feature from the FDI Host, the respective feature shall be listed in the feature table.

An FDI Package shall have only one Package Feature Table. The Package Feature Table shall be identified by a single package relationship.