A graph-based framework for model management system design is proposed in this paper. The framework applies graph theory to the development of a knowledge-based model management system, which has the capability of integrating existing models in the model base to support ad hoc decision making. In other words, models in the model base are not only stand-alone models but also building blocks for creating integrated models. This guarantees effective utilization of developed models and promises future development of an automated modeling system. In the framework, nodes and edges are used to represent sets of data attributes and sets of functions for converting a set of data from one format to another respectively. A basic model is defined as a combination of two nodes, one input node and one output node, and an edge connecting the two nodes. A model graph, which is composed of basic models, is a graph representing all possible alternatives for producing the requested information. Each path in a model graph is a model for producing the information. If the path includes more than one basic model, it represents an integrated model. Based on the graphical representation. an inference mechanism for model integration and strategies for model selection are presented.