This paper presents a vision of organizing models in two levels called the abstract space and the concrete space. At the concrete level, XML is the unique representation technology, whereas at the abstract level many different representation systems may be found, like UML or MOF. We argue that model transformation is becoming an important paradigm in many areas of information processing. As a consequence model transformation should be dealt with, both at the abstract and concrete level. Considering XSLT as the central transformation tool of the concrete space seems the obvious approach. Nevertheless other more abstract transformation languages should exist at the abstract level. As a consequence, we need to define translation schemes from these languages to XSLT, like one may translate from high-level languages to assembly languages. We show that the problem is more simplified if all the models and meta-models of the abstract space are based on the same meta-meta-model and if there is a canonical XML transformation defined in this meta-meta-model. We use the MOF and XMI standards of OMG to illustrate our approach.