HELM, hierarchical environment for linear modeling

Graduation date: 1989Several problems relating to linear programming modeling have\ud been identified: (1) model formulation, validation and explanation\ud are difficult and time consuming; (2) models must be frequently\ud updated and debugged; (3) flexibility is needed to specify the model\ud schema for a class of problems as a group; and (4) significant\ud differences exist between the way human model designers view a linear\ud programming problem and the way a problem must be specified for\ud solution by a computer.\ud The following methods are used to resolve these problems in\ud HELM: (1) allowing a broad class of similar problems to be specified\ud as a group by using a data-independent modeling language for the\ud model schema; (2) reduction of cognitive complexity of the modeling\ud process by separating model schema from data storage and data\ud acquisition; (3) increasing the range of models that can be specified\ud by delaying binding the specific variables, constraints, and\ud coefficients to be used for a particular instance of the models until\ud run time; and (4) providing a translation facility to convert the\ud model from a form convenient for a model designer to a standard\ud format for use by an optimization module.\ud This thesis describes the modeling language of the HELM\ud (Hierarchical Environment for Linear Modeling) system for\ud conceptualizing, organizing, and specifying the model schema of\ud large-scale linear programming problems. It shows how to transform\ud the standard linear programming form into the HELM model structure.\ud A formal detailed description of HELM syntax is provided and the HELM\ud process of model integration is described. The use of the system is\ud demonstrated with an example