1. The System Entity Structure: Using Simulation to Search and Optimize
Examples
Model Base Organization and Synthesis
System Entity Structure for Optimal crew size
Worker interference
Paper and Pencil Analysis

2. 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.

3. System Entity Structure Axioms
SES is represented as a labeled tree with attached attributes that satisfies the following axioms:
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
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.

4. aspect
entity
specialization

5. SES Example elevator freight floors contents cargo escalator pas-
carriage
specialization
physical
decomposition
motion
specialization
floors
contents
cargo
contents
specialization
escalator
pas-
senger
lift
people
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

6. SES Multiplicities multiple aspect multiple entity city roadNet city
roadSeg
traffic
Genr
(G)
Light
(L)
seg
line
road
Sched
(S)
step
event
city
multiple
aspect
roadNet
multiple
entity S G L
Seg
...
roadSeg
roadNet

7. System Entity Structure Inheritance e.g., Mapping into XML
specialized entities inherit their parents subtriee
vehicle
aluminum.airplane.vehicle
- density
= low
- strength
= medium
speed
= high
material
composition
decomposition
- density
- strength
transportation
class
- speed
decomposition
motor
transmission
propulsion
aluminum
steel
car
ship
airplane
- buoy
ancy
- density
= low
- strength
= medium
- speed
= high
motor
wood
transmission
wing.propulsion
wings
wheels
XML:
<object> aluminum.airplane.vehicle
<density> low
<strength> medium
<speed> high
<madeof>
motor
transmission
wing.propulsion
Rule: if select airplane from transportation
then
select aluminum from material composition
and wings from propulsion
Note: buoyancy field is not present

8. SES/Model Base: Synthesize new models from reusable DEVS components
Develop a
System Entity
Structure to
organize the
Repository
PES
transforming
pruning
hierarchical
DEVS
model
Repository
of DEVS
components

9. SES and UML as Ontologies
ontology
UML
SES
Classes
General things in the many domains of interest
yes x
Instances
Particular things
Relationships
among things
Generalization
/specialization
(a kind of)
associations (aggregations, composition (part of) dependencies,…)
labeled
specialization
decomposition
Properties
(and property values) of things
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