Added PIONE document of WorkflowPatterns No.1 Sequence.
Added PIONE document of WorkflowPatterns No2. Parallel Split.
Added PIONE document of WorkflowPatterns No.3 Synchronization.
Added PIONE document of WorkflowPatterns No.4 Exclusive Choice.
Added PIONE document of WorkflowPatterns No.5 Simple Merge.
Fixed an error of update criteria.
Modified #accept_nonexistence? to be sequential.
Changed the way of accepting nonexistence to be that data-null tuples
exist in it's domain.
Added PIONE document of WorkflowPatterns No.6 Multi-Choice.