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In contrast to the other parallel processing systems described in this section, Express  toolkit is a collection of tools that individually address various aspects of concurrent computation. The toolkit is developed and marketed commercially by ParaSoft Corporation, a company that was started by some members of the Caltech concurrent computation project.
The philosophy behind computing with Express is based on beginning with a sequential version of an application and following a recommended development life cycle culminating in a parallel version that is tuned for optimality. Typical development cycles begin with the use of VTOOL, a graphical program that allows the progress of sequential algorithms to be displayed in a dynamic manner. Updates and references to individual data structures can be displayed to explicitly demonstrate algorithm structure and provide the detailed knowledge necessary for parallelization. Related to this program is FTOOL, which provides in-depth analysis of a program including variable use analysis, flow structure, and feedback regarding potential parallelization. FTOOL operates on both sequential and parallel versions of an application. A third tool called ASPAR is then used; this is an automated parallelizer that converts sequential C and Fortran programs for parallel or distributed execution using the Express programming models.
The core of the Express system is a set of libraries for communication, I/O, and parallel graphics. The communication primitives are akin to those found in other message-passing systems and include a variety of global operations and data distribution primitives. Extended I/O routines enable parallel input and output, and a similar set of routines are provided for graphical displays from multiple concurrent processes. Express also contains the NDB tool, a parallel debugger that uses commands based on the popular ``dbx'' interface.