The System Entity Structure: Using
Simulation to Search and Optimize
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•
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System Entity Structure
Examples
Model Base Organization and Synthesis
System Entity Structure for Optimal crew
size
• Worker interference
• Paper and Pencil Analysis
System Entity Structure
• System Entity Structure (SES) represents a family of
hierarchical DEVS models
• Particular members of the family are generated by
process called pruning to generate a pruned entity
structure (PES)
• A hierarchical DEVS model ready to execute is
obtained by
transforming a PES, i.e., accessing
components in a repository and coupling them
together according to the PES specification.
System Entity Structure Axioms
SES is represented as a labeled tree with attached attributes
that satisfies the following axioms:
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alternating entity/aspect or entity/specialization:
Each node has a mode that is either entity/aspect or entity/specialization
such that a node and its successors are always opposite modes; the
mode of the root is entity.
Coupling is associated with aspects
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uniformity:
Any two nodes with the same names have identical attached variable
types and isomorphic sub-trees.
strict hierarchy:
No label appears more than once down any path of the tree.
valid brothers
No two brothers have the same label.
attached variables:
No two variable types attached to the same item have the same name.
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aspect
specializ
ation
entity
SES Example
elevator
physical
decomposition
floors
motion
specialization
carriage
specialization
contents
contents
specialization
people
cargo
lift
escalator
passenger
freight
Rule – if select freight from carriage spec
then select lift from motion spec
and select cargo from contents spec
Rule – if select passenger from carriage spec
then select people from contents spec
SES Multiplicities
city
city
roadNet
multiple
aspect
roadNet
roadSeg
multiple
entity
road
Sched
(S)
line
traffic
Genr
(G)
seg
step
traffic
Light
(L)
event
roadNet
roadSeg
S
Seg
G
Seg
L
...
Seg
S
Seg
G
Seg
L
...
Seg
S
Seg
G
Seg
L
...
Seg
System Entity Structure Inheritance
e.g., Mapping into XML
specialized
entities inherit
their parents
subtriee
vehicle
aluminum.airplane.vehicle
material
composition-
decomposition
- density
= low
- strength
= medium
speed
= high
transportation
class
density
- strength
- speed
decomposition
motor
transmission
propulsion
steel
wood
wings
wheels
aluminum
- density
= low
- strength
= medium
car
ship
- buoy
ancy
Rule: if select airplane from transportation
then
select aluminum from material composition
and wings from propulsion
airplane
- speed
= high
motor
transmission
wing.propulsion
XML:
<object> aluminum.airplane.vehicle
<density> low
<strength> medium
Note:
<speed> high
buoyancy
<madeof>
field is not
motor
present
transmission
wing.propulsion
SES/Model Base: Synthesize new models
from reusable DEVS components
Develop a
System Entity
Structure to
organize the
Repository
transforming
pruning
SES
PE
S
hierarchical
DEVS
model
Repository
of DEVS
components
SES and UML as Ontologies
ontology
UML
SES
Classes
General things in the
many domains of interest
yes
x
Instances
Particular things
yes
x
Relationships
among things
Generalization
/specialization
(a kind of)
associations
(aggregations,
composition (part of)
dependencies,…)
labeled
specialization
labeled
decomposition
Properties
(and property values) of
things
instance variables and
values
instance variables and
values
Functions
Functions of, and
processes, involving
things
sequence diagrams
collaboration diagrams
pruning to generate
models from family
specified by SES
Constraints
on, and rules, involving
things
no
synthesis constraints
selection constraints