Explicit and Implicit Resources:
A Simplified Approach to User Requirements Modeling

Jeff Hagopian, Theresa Maxwell
jeff.hagopian@msfc.nasa.gov 
NASA/MSFC


Abstract:
The International Space Station (ISS) program is  heavily dependent on the
concept of distributed  planning. Within the payload planning community, the 
concept of distributed planning places a great deal of  responsibility in the
hands of the science users. This  approach to planning is very different from
that used  within the current Shuttle and Spacelab programs,  where much of
the responsibility for planning resides  with the control center personnel. In
the Shuttle and  Spacelab programs the control center personnel  interface
with the science users to obtain the  requirements for the operations to be
scheduled. These  requirements are then translated by the scheduling  experts
into the format required for use by the  scheduling software. Within the ISS
program, the  interface to the control center personnel has been  radically
altered. The users will assume the  responsibility for submitting requirements
in the  format required for use by the scheduling software.  Therefore, it is
extremely important that requirements  modeling software be provided which
enables  non-scheduling experts to define their requirements.  The
requirements modeling process is further  complicated by the very complex
nature of the ISS  systems against which requirements must be defined. 
Therefore, it is desirable for this requirements  modeling software to not 
only support novice users,  but also to conceal from them the complexities of
the  station systems. The concept of explicit and implicit  resources has been
developed to support these two key  requirements. Explicit resources are those
resources  that are directly requested by a science user in defining 
scheduling requirements. Implicit resources are those  resources not directly
requested by the science user,  but associated with the user's requirements by
the  modeling software through the use of functional  relationships and modes.
This paper defines and describes the concept of explicit and implicit 
resources, provides examples of scheduling  requirements implemented using
explicit and implicit  resources, and discusses the software currently being 
developed to support this concept.