The source navigation based model associates each location with primitive operations, and it assumes that an implementation of these operations can be derived from metadata of the location. The next step towards building a code generator is therefore the design of an appropriate metadata model, which defines the names and semantics of metadata items. This section introduces a model which is intended to minimize the effort required for implementing a transformation. Metadata items are represented by attributes of a location tree ([3]), so that a transformation is specified by editing a location tree augmented by metadata attributes.