  We suggest there is a need for a fresh perspective on the design and
development of workflow systems and argue for a building blocks approach. We
outline a description of this approach and define the properties of software
building blocks. We discuss RADICAL-Cybertools as one implementation of the
building blocks concept, showing how they have been designed and developed in
accordance with this approach. Four case studies are presented, covering a
dozen science problems. We discuss how RADICAL-Cybertools have been used to
develop new workflow systems capabilities and integrated to enhance existing
ones, illustrating the applicability and potential of software building blocks.
In doing so, we have begun an investigation of an alternative approach to
thinking about the design and implementation of workflow systems.
