Per feedback from Barry, was reviewing XML processing and because we execute all queries serially in our XML processing. However, conceptually, we could often execute multiple mapping class and/or temp table queries in parallel. When time permits it might be benefitial to investigate this.

All mapping classes at depth "n" in the document model are independent of each other, so they can be executed in parallel. Each mapping class may have input sets to any ancestor mapping class up to depth "n-1", or may select from any temp table up to depth "n" (the same depth).