Hi Folks,

I am seeking a powerful, declarative XML language for expressing reversible transformations.

Here is an example to illustrate what I mean by reversible transformation. Input files contain an integer denoting a machine: 0 denotes Intel 386, 1 denotes x86, 2 denotes ARMv7. Here is an input file transformed to XML:

1 à foo à <machine>x86</machine>

where foo is some (to-be-determined) declarative, XML language.

Here is the reverse transformation, from XML to original input format:

<machine>x86</machine> à foo à 1

To do this reversible transformation, foo must have (declaratively) captured the mapping from integers to strings (e.g., 1 -> x86).

That level of reversible transformation is already possible using the declarative, XML language Data Format Description Language (DFDL). DFDL calls these transformations parsing and unparsing.

Here is an example of a more advanced reversible transformation. An input file has this:

W014404 1217          

where:

W means West
014404 means 14 degrees, 40.4 minutes
1217 means the month and year of variation (e.g., December 2017)

The input file is transformed to this XML:

<magneticVariation>
    <magneticVariationEW>West</magneticVariationEW>
    <magneticVariationValue>15.0</magneticVariationValue>
</magneticVariation>

The reverse transformation takes the XML back to the original input format.

To do this reversible transformation, a language must have (declaratively) expressed:

• the mapping from characters to strings (e.g., W -> West)
• the mapping from degrees/minutes to decimal degrees (e.g., 014404 -> 15.0)
• the mapping from month/year of variation to null (e.g., 1217 -> null)

That kind of reversible transformation requires a powerful language. Unfortunately, DFDL cannot (yet) express that kind of reversible transformation.

Do you know of a powerful, declarative, XML language for expressing reversible transformations?

/Roger