VISUAL MODELING FOR PRODUCTION AND TRANSPORTATION SYSTEMS

Abstract

This thesis presents an exploration on visual modeling with structured modeling paradigm and object-oriented concept and aims at providing the three group of users (Bharadwaj et al. 1992) with a user-centered approach to facilitate model building in Production-Transportation System (PTS) as well as in the other application domains. Structured Modeling (SM) (Geoffrion 1987, 1989c, 1990c) is a systematic modeling framework which provides a sound theoretical basis to represent a wide variety of models and can be broadly applied in various application domains. By using its definitional system as an underlying modeling framework in the thesis, a visual model representation with object-oriented properties called Structured and Object-Oriented Model (SOOM) is proposed. SOOM provides a kind of decision model representation in which the components comprising the model are object-oriented classes or objects and the interrelations among components are structured. Moreover, SOOM also provides a foundation of step-wise model building (abstracting model through specialization) (Lazimy 1993) clue to its object-oriented properties. Under this kind of representation, three levels of model and two stages of visual modeling are identified. The three levels of model are meta model, domain model and specific model. Meta model is represented in both directed acyclic attributed graph and generic object-oriented class. Domain oriented generic visual model or domain model is a specialization of meta model in a specific problem domain and specific model is the instantiation of domain model. The two stages of visual modeling, approaches are Generic Visual Modeling (GVM) and Specific Visual Modeling (SVM). GVM is a domain-independent modeling approach which is used for building domain models for certain application domains by domain experts who have modeling knowledge and some modeling skills. SVM is a domain-dependent approach derived from GYM for end-users or decision makers to derive a specific model from its domain model and use it to solve their decision problems. Along with these two stages of visual modeling, a visual modeling language VML is designed, which facilitates building syntactically-correct visual models intuitively. GVM is general purpose and is therefore kept consistent no matter what the application domain is. However, different application domains will have different domain models which, in turn, result in different S VM. SVM is targeted at end-users in a specific domain. By summarizing the discussions of model representation and modeling approaches, a general modeling visualization schema is presented which facilitates construction of visual modeling systems to satisfy the different needs of users. Based on the proposed model representation and modeling approaches a research prototype, (VMS/SM) is implemented under WindowsTM to validate the concepts and approaches we have proposed and provide an integrated modeling environment for both modeling professionals and non-professionals to deal with PTS models. The system has a uniform graphical user interface and two modeling subsystems: GYM and SVM. In the system, a model is represented with both a directed attributed acyclic graph and an object-oriented class or object. The graph representing a model can be seen and is easy to understand and manipulate. It provides the external conceptual-schema view of a model for users. The object-oriented representing model specifies the internal object-oriented implementation details and is computer executable. It is hidden from users and takes advantages of object-oriented characteristics. Due to the basis of SM and the integration of GVM and SVM, this system is actually domain independent and can be used to benefit both professional modelers and end-users in application domains other than PTS as well. The main contributions of this research project are therefore I) the proposal of model representation SOOM; 2) the two stages of visual rnodeling approaches based on SOOM; 3) A visual modeling language that adopts the proposed paradigm to facilitate model syntax-directed editing; 4) A general modeling visualization schema that facilitates the construction of visual modeling systems to satisfy the different needs of users; and 5) an implementation of a visual modeling prototype that integrates GYM and SVM in a single modeling system and demonstrates the effectiveness of our research.