Even though the development of sophisticated join processing techniques started in the early Eighties, there are still substantial improvements possible. The need for further investigating join processing techniques is a result from the ever larger growing database volumes (i.e., in data warehouse applications) that need to be processed.

Helmer, Westmann and Moerkotte developped a new join processing technique, called DiagJoin, for processing the join of hierarchical master/detail (i.e., 1:N) relationships. Their processing technique is applicable for database configurations in which the master tuple and the detail tuples are created at the same time and clustered accordingly. Even though, this restricts the applicability of their technique, such configurations are frequently found in data warehouse applications where tuples are usually appended to the database. An important example is the Order/Lineitem schema - an Order (the master) is usually created together with its Lineitems (the details).

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