This paper presents an approach to the design of digital libraries by raising and addressing issues involved in supporting services for collections of structured, semi-structured and unstructured objects. We present a system architecture for a digital library that includes provisions for storing and retrieving data with differing structure levels (ranging from highly unstructured to highly structured). We have successfully instantiated this architecture via a practical implementation that integrates technologies such as relational and novel XML databases as well as indexing and information retrieval techniques. A number of digital library applications are using these facilities for handling differing structure levels in an integrated fashion.