Scientific computer models are most often implemented in FORTRAN, Pascal, and C, which are general computer languages. When a researcher other than the model author sets out to use a model, he or she is often faced with problems in understanding how that code works. These problems include:
Ecosystem modellers need better technology to facilitate building, sharing and reusing their models. The Scientists' Intelligent Graphical Modelling Assistant (SIGMA) creates an environment for model building, sharing and reuse which provides an alternative to more conventional approaches which too often yield poorly documented, awkwardly structured model code.
Dr. Richard Keller and colleagues in the Computational Sciences Division have built SIGMA to address the abovementioned problems with scientific model implementation. The SIGMA interface provides a list of model quantities which can be selected for computation. Equations to calculate the model quantities may be chosen from an existing library of ecosystem modelling equations, or built using a specialized equation editor Inputs for these equations may be supplied by data or by calculation from other equations. Each variable and equation is expressed using ecological terminology and scientific units, and is documented with explanatory descriptions and optional literature citations. Automatic scientific unit conversion is supported and only physically-consistent equations are accepted by the system. The system uses knowledge-based semantic conditions to decide which equations in its library make sense to apply in a given situation, and supplies these to the user for selection. The equations and variables are graphically represented as a data flow diagram which provides a complete summary of the model.
Forest-BGC (Running and Coughlan 1988), a stand-level model that simulates photosynthesis and evapotranspiration for conifer canopies, was originally implemented in Fortran and subsequently reimplemented using SIGMA. The SIGMA version reproduces daily results and also provides a knowledge base which greatly facilitates inspection, modification and extension of Forest-BGC.
Jennifer Dungan, JCWS, Inc.
USmail: Mail Stop 242-4
NASA Ames Research Center
Moffett Field, CA 94035-1000
Phone: (650) 604-3618
FAX: (650) 604-4680
Dr. Richard Keller is the principal investigator on the project.
A fuller description of the SIGMA system, including technical reports, a tutorial and other applications can be reached from the SIGMA home page
SIGMA is funded by NASA's Applied Information Systems Research and Mission Operations programs.
Ames Research Center Home Page ECOSAT Home Page
Information last updated: 7/26/95