Structured information data sets structured according to a first predefined structure are converted into data sets structured according to a second predefined structure by way of an intermediate data structure. Conversion rules are defined to convert from each of the first and second predefined structures into the intermediate data structure and from the intermediate data structure into each of the first and second predefined structures. A pre-processor is provided to carry out initial processing tasks on a received data set to make it more susceptible to structural processing according to the conversion rules, and a post-processor is provided to carry out tasks such as vocabulary and data type conversion.