S3 (Softwood Sawmill Simulator) is a sawmill simulation system for modeling the operations of Pacific Northwest softwood lumber mills. S3 consists of three main parts. The first part is the framework for construction of the sawmill layout. The second part focuses on individual machine centers, their process and down times, and their interconnections. The third part consists of databases for raw material and final products. S3 inputs process logic from external data files. All parts are integrated in an object-oriented framework. The system was developed using the object-oriented environment, Actor. All data input and output are through database files in dBASE IV format. S3 can model a sawmill represented by the machine center and connection types defined in S3. The size of the model is controlled by the Actor programming environment. The construction of a sawmill model is demonstrated. / Graduation date: 1993