== Workflow interpreter and processor

   flow.rb is a utility for running job workflows in 
   DRMAA-compliant DRM systems. Workflows are specified in 
   flowfiles that allow expression of

     * concurrent and sequential execution of sub-flows
     * multiple runs of sub-flows with varying parameter sets
     * actual jobs are defined in terms of DRMAA attributes
   
   in addition any subflow or sets of subflows can be run
   as used with make(1) by specifying it as target.

=== Job defaults

   To minimize the extent of attributes necessarily
   specified in flowfiles, flow.rb provides defaults for 
   jobs' command path, stdout/stdin path, current working
   directory and job name.

=== Workflow verification

   The -verify option can be used to print dependencies and
   job attributes for diagnosis purposes.  To ensure each
   workflow job can be run, a number of verifications is 
   performed before the first job gets submitted.

=== Job streaming

   Large workflows are automatically run in job streaming mode
   upon DRM saturation and a job maximum can be set in .flowrc.rb
   to place an upper limit of jobs be kept concurrently in the
   DRM for each workflow.

=== Pre-submission plug-in

   Enforcement of site-specific policies can easily be 
   achieved through pre-submission procedures that allow
   any job attribute to be modified freely.