Transforming a user-supplied DTD satisfying a first XML grammar into a PDTD satisfying a second XML grammar, including converting DTD declarations of alternate content to sequences, converting DTD declarations of optional content to mandatory content, converting DTD declarations of imbedded sequences to subsequences, and demoting attribute definitions of DTD elements having attributes to children of the DTD elements having attributes. Embodiments include converting recursions into repetitions, demoting imbedded compound repetitions from element declarations having imbedded compound repetitions, and demoting imbedded leaves from elements having imbedded leaves.