ZapNote: B-Bop
The only true solutions for enterprise-wide XML data storage and retrieval are XML-enabled RDBMS and Native XML Data Store (NXD) approaches. The challenge with XML-enabled RDBMS is that they are not very well suited to highly extensible and flexible documents, while the challenge with NXDs is that they are unproven technologies with very small user bases. However, there is another option that is a sort of "middle ground": the use of an interpretive middle layer over standard RDBMS systems that offers schema-independent, "native" XML data storage. In this vein, B-Bop offers their Xfinity Server as a way of providing the features of Native XML storage while utilizing existing relational storage architectures.
B-BOP: XFINITY SERVER LEVERAGING RELATIONAL DATABASES FOR XML STORAGE