I'm working with the Australian DSTO Flight Systems Branch on develoment of generic aircraft flight models. We are basing the datasets for this work on the DAVE-ML DTD, with reasonable success so far. Our datasets are used by loading directly into a DOM encapsulated in a C++ class which performs function evaluations based on the XML dataset and returns the results to the calling function.
However, our work to date indicates an addition to the DTD would be useful. I propose that the independentVarRef element be modified as shown below: <!ELEMENT independentVarRef EMPTY> <!ATTLIST independentVarRef varID IDREF #REQUIRED min CDATA #IMPLIED max CDATA #IMPLIED extrapolate (neither | min | max | both) #IMPLIED interpolationType CDATA #IMPLIED interpolationOrder CDATA #IMPLIED > The justifications for this change are: For tabulated data in any form, the type of interpolation/extrapolation applicable should be dependent on the data, not on the software in use to interpret the data. It is therefore appropriate to include interpolation instructions in the XML dataset. A variable may be interpolated differently in different functions within the same dataset. Interpolation instructions therefore belong in the independentVarRef rather than in the variableDef. An alternative would be to include the interpolation instruction in the bpRef attributes for each function, if that was thought preferable. Examples of the most common entries for these attributes are: interpolationType="polynomial" interpolationOrder="1" which results in linear interpolation in the relevant degree of freedom, with continuity of the function, but not of its derivatives, across the breakpoints. Setting order to "0" allows discrete values, while higher order can be chosen if required for rapidly-changing data. Alternative interpolation types can represent different methods, such as "c-spline", or different choice of basis functions, such as "legendre". In future, it might also be useful to add further options to the "extrapolate" attribute to determine whether the extrapolating basis function is the same as that used for interpolation. We await with interest any comments or suggestions.