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Discrete Event Process Models and Museum Curation. Louis G. Zachos Ann Molineux Non-vertebrate Paleontology Laboratory Texas Natural Science Center The University of Texas at Austin. Discrete Event Simulation. What is DES?

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discrete event process models and museum curation

Discrete EventProcess ModelsandMuseum Curation

Louis G. Zachos

Ann Molineux

Non-vertebrate Paleontology Laboratory

Texas Natural Science Center

The University of Texas at Austin

discrete event simulation
Discrete Event Simulation
  • What is DES?
  • Many processes can be represented as a series of discrete events or activities.
discrete event simulation1
Discrete Event Simulation
  • Events occur at an instant in time, persist for some period of time, and mark a change of state in the process – they are the individual – discrete - steps in the staircase of a process.
  • DES is a computational (i.e., computer) model of a system of real-life processes modeled as multiple series of discrete events
functionality of des modeling environment
Functionality of DESModeling Environment
  • In practical terms, a DES is comprised of a model and the environment in which it is executed
  • It is possible to design a DES as a single computer program – but there is software to create a modeling environment for a DES
des modeling environment components house keeping functions
DES Modeling EnvironmentComponents(House-Keeping Functions)
  • Clock
  • Random Number Generators for a Variety of Probability Density Functions
  • Statistics Collation and Graphing Capability
  • Events, Resources, Stores Lists Handling
  • Conditions and System State Handling
simpy sim ulation in py thon
SimPySimulation in Python
  • An Open Source object-oriented discrete-event simulation language based on
  • “Many users claim that SimPy is one of the cleanest, easiest to use discrete event simulation packages!” (from http://simpy.sourceforge.net/)

http://simpy.sourceforge.net/

process object model
Process Object Model
  • DES in SimPy is based on the definition of ObjectClasses
  • There are 3 classes:
  • Process class – the object that “does something”
  • Resource class – objects required to “do something”
  • Monitor class – an object to record information
model design
Model Design
  • A system can be decomposed in a top-down, hierarchical manner
  • Start with the most general
model design1
Model Design
  • Break each process into sub-processes
resources
Resources
  • Resources are things like people, cameras, computer workstations, etc. – required to perform processing.
stores
Stores
  • The entities being processed – museum specimens – are represented as stores
  • Stores act like queuing bins -
npl model
NPL Model
  • Photography of type specimens
  • Scan labels
  • Prepare and scan
  • Photograph specimens
  • Prepare and photograph
  • Convert raw imagery
  • Process multi-focus imagery with Helicon
  • Cleanup and standardize imagery in Photoshop
npl model1
NPL Model
  • Resources
  • People
  • Cameras
  • Computer workstations
  • Stores – fossil specimens and labels
  • Simplest case – individual resources are alike
  • Variability is modeled stochastically
modeling results
Modeling Results

Can capture various aspects of a process and realistically model throughput and variability

modeling results1
Modeling Results

Bottlenecks in the process become readily apparent – in this example the process waits on human resources – just adding another camera would not improve throughput

validation
Validation
  • Model results must be validated against actual system throughput
  • Actual process is timed and variability modeled
extrapolation
Extrapolation
  • Once a working model has been validated:
  • Bottlenecks can be quantified
  • The effects of varying resources or changing order of processes can be evaluated
  • Reliable estimates of time to completion for entire projects can be made
conclusion
Conclusion
  • Discrete event simulations can be a useful tool for evaluating long-term projects in the museum environment
  • The methodology makes the results easier to justify for budget or grant applications
  • The development of a model aids in understanding the underlying processes