A flexible method to store XML documents in relational or object-relational databases is presented that is based on an adaptable fragmentation. Whereas most known approaches decompose XML documents into minimal units we propose to store fragments of variable granularity ranging from single elements to whole documents. Different fragmentation strategies depending on the specific access and query requirements can be applied to the same XML documents. Experiments have shown that the response times are much better than those for the complete decomposition. Furthermore, our storage model which is based on directed acyclic graphs facilitates the reuse of XML subdocuments and supports different views on XML documents.