Fundamental Problem
Essence of a “science”






Observation
Categorization/classification
Abstraction
Symbolic representation
Manipulation
Prediction
Solving the Problem
Creating a Reference Model

Look for a reasonably small set of
organizing principles



Propose reference model elements
Check for consistency
Refine
Reference models
are artifacts, not
natural phenomena
Engineering Examples



Structural engineering, GTSTRDL, SAP
Solid modeling, FEA
Circuit design, SPICE, VHDL
Solving the Problem
Modeling principles for developing
a logistics reference model:
• Observability
• Minimum inferred structure
Solving the Problem
Key (Observable) Warehouse
Elements
WarehouseEquipment
Resources
Entities:
Labor
Labor
Equipment
Space
Goods
Goods
Orders
Customer Orders
Filled
Activities: changes to entities’ states
Customer
Orders
Solving the Problem
What CAN’T be observed?
Decision-making!
Hypothetical models of decisionmaking
Solving the Problem


Make a “theory” of decision making
Make it as simple as possible, consistent with
observed effects of decision-making, but no
simpler
Minimum
structure
This
doesinferred
not require
designing the control system.
Solving the Problem
Organizing Principle #1
• Warehousing resources and activities are
organized by departments
• Generic set of department types (or classes)




Receiving
Transportation
Storage
Fast picking




Sortation
Packing
Shipping
Value adding services
Generic Organization of
Resources
Department
Classes
Resource Types
Equipment
Classes
Labor
Class
Space
Class
Product
Class
Order
Class
Product
Instances
Order
Instances
Department
Set
Equipment Employees
Space
Instances
Instances
Resource Instances
Department
Instances
Solving the Problem
Solving the Problem
Object Models for Resources

Trust me, it’s straightforward

Even if it’s not unique
Solving the Problem
Organizing Principle #2
• Activities are organized into departmentspecific tasks
• Generic set of task types (or classes)



Receiving: Unload/receive
Transport: Put-away;
retrieve; replenish
Pallet Storage: Pick pallet;
case pick to pallet



Fast picking: single order
pick; multiple order pick
Sortation: sort
Shipping: unitize pallet;
pack & ship items; ship
pallet; load pallet
Solving the Problem
Organizing Principle #3
• Tasks correspond to flow in a functional
network
Inspection
Order picking
Receiving
Bulk storage
Carton storage
and picking
Material flow
Shipping
Order sort/
accumulate
Function-to-department mapping
• Handling unit conversions
• Processing options
• Total workload
Solving the Problem
Organizing Principle #4
• Warehousing tasks are composed from
fundamental warehouse operations
• Generic set of operation types (or classes)





Move
Retrieve
Store
Get
Put





Count
Weigh
Measure
Scan
Communicate
Solving the Problem
Operation Reference Model
The associated operations reference model is simply:
do opn-ID using {res_ID} to {handling_unit_ID} from origin_loc_ID to dest_loc_ID
where:
opn-ID
{res_ID}
{handling_unit_ID}
origin_loc_ID
dest_loc_ID
indicates what operation type to perform
indicates which resource(s) to use
indicates what is to be operated on, i.e., a container
or goods ID
indicates the starting location
indicates the ending location
Solving the Problem
Assertion

The (time stamped) log of operations reports
the complete state trajectory of the warehouse
Generic Organization of
Operations
Task
Classes
Operation Types
Get/Put
Store/Retrieve
Move
Count/Weigh/
Scan/Measure
Specific
Task Set
Transactions
Transactions Transactions Transactions
Operation Instances
Task
Instance
Solving the Problem
Solving the Problem
Description  Prediction
We can describe instances of resources
and operations or tasks.
We can log operations and summarize
historical state changes
But we still can’t predict behavior
Why?
Solving the Problem
Organizing Principle #5

Warehousing tasks/operations are event driven
Warehouse
State Data
External
Events
Event
Message
Warehouse
Physical
structure
Resources
Event is a THEORY,
Task
This
Monitor
Generator
not a model of any
specific WMS
Timer
Operation
(command)
Operation
Manager
Inferred
structure of
warehouse
decision
making
process
Solving the Problem
Bad News and Good News


Bad: Task generators are specific to the
warehouse design, because they are specific to a
department instance!
Good: But there may be typical elements of
task generators
Solving the Problem
Location Assignment Decisions




Truck to dock
Product family to zone
Goods to/from storage location
Order to accumulation lane
Solving the Problem
Grouping/Partitioning Decisions




Products to families
Locations to zones
Orders to waves
Lines to zones/pickers
Solving the Problem
Sequencing/Routing Decisions




Transport routing
Pick sequencing/routing
Retrieval sequencing
Storage/retrieval interleaving
Solving the Problem
Is there an exhaustive class of
decision types just as there are
classes of resources and of tasks?
This would be a good thing!
What are the organizing principles?