Browsing by Author "Overstreet, C. Michael"

Now showing 1 - 8 of 8
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    Diagnostic Assistance Using Digraph Representation of Discrete Event Simulation Model Specifications
    Overstreet, C. Michael; Nance, Richard E. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1986-03-01)
    Automated diagnosis of digraph representations of discrete event simulation models is illustrated as an effective model verification technique, applicable prior to coding the model in an executable language. The Condition Specification is shown to provide an effective representation, from which automated analysis can initiate with a digraph extraction. Subsequent diagnostic simplification techniques are applied to the digraph, either automatically or in concert with the modeler.
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    Graph-based Diagnosis of Discrete Event Model Specifications
    Overstreet, C. Michael; Nance, Richard E. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1983)
    Several diagnostics which assist in the construction of specifications for discrete event simulation models are defined. The model specifications to be analyzed must be in a particular form called a Condition Specification. The diagnostics are based on analysis of graphs easily derived from a Condition Specification. Most of the diagnostics are intended to be applied as a Condition Specification is being developed. Th ree categories for the classification of diagnostics of model specifications are defined. Two examples illustrate the graphical forms derivable from a Condition Specification.
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    Model specification and analysis for discrete event simulation
    Overstreet, C. Michael (Virginia Polytechnic Institute and State University, 1982)
    Several authors assert that any significant improvement in the efficiency in the development and utilization of simulation models requires the assistance of a Model Management System to automate much of the process. This work develops one aspect of such system: tools fundamental to the specification and analysis of discrete event models. A model specification language is developed which allows analysis of a model specification as the specification is being developed. Model analyses are discussed which (1) detect several types of errors in a model specification, (2) automate the generation of many types of documentation useful during model development and the generation of model documentation useful during the model life cycle, (3) improve model implementations by assisting in the choice of a world view and implementation technique. A model specification in this language is called a condition specification (CS). Formal procedures are developed to transform a cs into a model specification in any of the three traditional worldviews of event scheduling, activity scanning, and process interaction. These transformation procedures are supported by a careful definition of the equivalency of model specifications and by a characterization of each of the three world views. Results are proved which show that the approach of each worldview transformation is valid (i.e., result in equivalent model specifications). This is necessary since the transformation procedures may delete parts of a CS. Both the characterization of each world view and the procedures that transform a cs into each world view provide a better understanding of the nature of each worldview than has existed to date. Several necessary properties for error-free model specifications are identified and defined. While useful test procedures for these properties can be developed, most of these properties are shown to be unverifiable in an absolute sense. That is, it is proved that no algorithm is possible which can detect every instance of several important model specification errors.
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    Simulation Model Management: Resolving the Technological Gaps
    Nance, Richard E.; Mezaache, Ahmed L.; Overstreet, C. Michael (Department of Computer Science, Virginia Polytechnic Institute & State University, 1981)
    Model management poses requirements and responsibilities that extend throughout the life cycle of a simulation model. Recent publications have identified major problems in cost and time overruns, which are traceable to deficiencies in project and sponsor management. Beginning with the division of the simulation model life cycle into seven phases, we define "model management" and develop the requirements for a Model Management System (MMS). The functional description of a MMS focuses on those phases that jointly characterize the model development effort. Recent research in simulation model development is described, and particular emphasis is given to the approach taken with the Conical Methodology.
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    Simulation modeling methodology: principles and etiology of decision support
    Page, Ernest H. (Virginia Tech, 1994)
    Investigation in discrete event simulation modeling methodology has persisted for over thirty years. Fundamental is the recognition that the overriding objectives for simulation must involve decision support. Rapidly advancing technology is today exerting major influences on the course of simulation in many areas, e.g. distributed interactive simulation and parallel discrete event simulation, and evidence suggests that the role of decision support is being subjugated to accommodate new technologies and system-level constraints. Two questions are addressed by this research: (1) can the existing theories of modeling methodology contribute to these new types of simulation, and (2) how, if at all, should directions of modeling methodological research be redefined to support the needs of advancing technology. Requirements for a next-generation modeling framework (NGMF) are proposed, and a model development abstraction is defined to support the framework. The abstraction identifies three levels of model representation: (1) modeler-generated specifications, (2) transformed specifications, and (3) implementations. This hierarchy may be envisaged as consisting of either a set of narrow-spectrum languages, or a single wide-spectrum language. Existing formal approaches to discrete event simulation modeling are surveyed and evaluated with respect to the NGMF requirements. All are found deficient in one or more areas. The Conical Methodology (CM), in conjunction with the Condition Specification (CS), is identified as a possible NGMF candidate. Initial assessment of the CS relative to the model development abstraction indicates that the CS is most suited for the middle level of the hierarchy of representations — specifically functioning as a form for analysis. The CS is extended to provide wide-spectrum support throughout the entire hierarchy via revisions of its supportive facilities for both model representation and model execution. Evaluation of the pertinent model representation concepts is accomplished through a complete development of four models. The collection of primitives for the CS is extended to support CM facilities for set definition. A higher-level form for the report specification is defined, and the concept of an augmented specification is outlined whereby the object specification and transition specification may be automatically transformed to include the objects, attributes and actions necessary to provide statistics gathering. An experiment specification is also proposed to capture details, e.g. the condition for the start of steady state, necessary to produce an experimental model. In order to provide support for model implementation, the semantic rules for the CS are refined. Based on a model of computation provided by the action cluster incidence graph (ACIG), an implementation structure referred to as a direct execution of action clusters (DEAC) simulation is defined. A DEAC simulation is simply an execution of an augmented CS transition specification. Two algorithms for DEAC simulations are presented. Support for parallelizing model execution is also investigated. Parallel discrete event simulation (PDES) is presented as a case study. PDES research is evaluated from the modeling methodological perspective espoused by this effort, and differences are noted in two areas: (1) the enunciation of the relationship between simulation and decision support, and the guidance provided by the life cycle in this context, and (2) the focus of the development effort. Recommendations are made for PDES research to be reconciled with the “mainstream” of DES. The capability of incorporating parallel execution within the CM/CS approach is investigated. A new characterization of inherent parallelism is given, based on the time and state relationships identified in prior research. Two types of inherent parallelism are described: (1) inherent event parallelism, which relates to the independence of attribute value changes that occur during a given instant, and (2) inherent activity parallelism, which relates to the independence of attribute value changes that occur over all instants of a given model execution. An analogy between an ACIG and a Petri net is described, and a synchronous model of parallel execution is developed based on this analogy. Revised definitions for the concepts time ambiguity and state ambiguity in a CS are developed, and a necessary condition for state ambiguity is formulated. A critical path algorithm for parallel direct execution of action clusters (PDEAC) simulations is constructed. The algorithm is an augmentation of the standard DEAC algorithm and computes the synchronous critical path for a given model representation. Finally, a PDEAC algorithm is described.
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    A Specification Language To Assist In Analysis Of Discrete Event Simulation Models
    Overstreet, C. Michael; Nance, Richard E. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1983)
    The use of effective development environments for discrete event simulation models should reduce development costs and improve model performance. A model specification language to be used in a model development environment is defined. This approach is intended to reduce modeli ng costs by interposing an intermediate form between a conceptual model (the model as it exists in the mind of the modeler) and an executable representation of that model. As a model specification is being constructed, the incomplete specification can be analyzed to detect some types of errors and to provide some types of model documentation. The primitives to be used in this specification language, called a Condition Specification, are carefully defined. A specification for the classical patrolling repairman model is used as an example to illustrate this language. Some types of diagnostics which are possible based on such a representation are summarized, as well as some model specification properties which are untestable.
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    Specification Languages: Understanding Their Role in Simulation Model Development
    Overstreet, C. Michael; Nance, Richard E.; Balci, Osman; Barger, Lynne F. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1987)
    Current software specification techniques and specification languages are reviewed, emphasizing research activities in software specification languages. Alternate software life cycle models are described and compared to a simulation life cycle model. The importance of constructing a model specification before creating a programmed model is emphasized. Disadvantages in using simulation programming languages as model specification languages are discussed. The multiple uses which are made of a model specification are presented; these uses correspond to the alternate uses made of a requirements specification for general software. To evaluate where specification tools for general software will be effective for simulation modeling, both areas where the simulation life cycle corresponds to a general software life cycle and areas in which they differ are characterized. Important
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    A visual simulation support environment based on a multifaceted conceptual framework
    Derrick, Emory Joseph (Virginia Tech, 1992-04-05)
    This thesis presents the development of a multifaceted conceptual framework for discrete-event simulation and its implementation within an integrated visual simulation support environment (VSSE). The intertwined research objectives regarding the conceptual framework and the companion VSSE are presented. A literature review of related work is conducted. The core of the thesis describes the conceptual framework (called the DOMINO), the VSSE and each of the tools from its supporting toolset, and the VSMSL (Visual Simulation Model Specification Language). Three example model applications (bus route, traffic intersection, and branch operations examples) demonstrate the use of the VSSE and the underlying DOMINO. The thesis is evaluated using the research objectives as assessment criteria. The DOMINO is truly multifaceted. Both graphical and object-oriented, the DOMINO provides design and implementation guidance over the simulation model life cycle. The DOMINO is not restricted to specific problem domains but is independent of application domain. Several different perspectives for developing model component logic are available to modelers under the VSMSL. The VSSE demonstrates significant advances in integrated, automated support for model development which include graphical facilities for definition and specification and effective verification techniques. The VSSE underscores the contributions of the research effort and has helped to identify potential areas for future research.