In this paper, we describe ongoing research in three DL projects that build upon a common foundation: the 5S DL framework. In each project, we extend the 5S framework to provide specifications for a particular type of DL service and/or system - finally, moving towards a DL reference model. In the first project, we are working on formalizing content-based image retrieval services in a DL. In the second project, we are developing specifications for a superimposed information-supported DL (combining annotation, hypertext, and knowledge management technologies). In the third effort, we have used the 5S framework to generate a practical DL system based on the DSpace software.