Integration of heterogeneous information resources has been one of the most important issues in recent advanced application environments. In addition to conventional databases, structured documents have been recognized as important information resources recently. In this paper, we present a data model named the NR/SD model, which is used as a basic data modeling framework for the seamless integration of structured documents and relational databases. The NR/SD model combines an abstract data type named the structured document type and the nested relational structures, and features operators named converters to dynamically convert structured documents into nested relational structures and vice versa. Therefore, we can manipulate information in either forms of structured documents and relations. The operators can also be used to develop user views on the stored structured documents and relations. We show data structures and operators in the NR/SD model and its applicability to system federation environments. Some basic properties of the converters are also studied.
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