This chapter has given an overview of how to integrate relational database systems with XQuery. It introduced the XML datatype and presented both the mixed approach of using XQuery in conjunction with SQL to query XML datatype instances and the top-level XQuery approach of querying collections of XML instances and XML views of relational data. It also provided an insight into the impact of the actual physical data model of the XML datatype on the processing and mapping of XQuery in the context of relational systems. Many relational database systems at the time of this writing have just started to add native XML support to their support for bidirectional mapping between relational and XML data, and so far no system ships XQuery as described in this chapter. Before long, however, I believe all major relational database systems will provide functionality of the form described (most vendors have already announced support for a built-in XML datatype). Many open issues need further investigation and are currently active research topics. Among them are the following:
|