Description logics have been designed and studied in a modular way. This has allowed a methodic approach to complexity evaluation. We present a way to preserve this modularity in encoding description logics in XML and show how it can be used for building modular transformations and assembling them easily. 1 Motivation In the words of Tim Berners-Lee, the "semantic web" [2] requires a set of languages of increasing expressiveness such that anyone can pick up the right language for each particular semantic web application. This is the approach taken by the description logic community over the years. We show how the modularity of description logics, that has mainly be used at a theoretical level, can be turned into an engineering advantage in the context of the semantic web. For that purpose, we introduce a description logic markup language (DLML) which encodes description logics in XML and preserves their modularity. We then present transformations that are described on indivi...