Essence of a “science”

1. Fundamental Problem Essence of a “science” • Observation • Categorization/classification • Abstraction • Symbolic representation • Manipulation • Prediction Reference Model

2. 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

3. Engineering Examples • Structural engineering, GTSTRDL, SAP • Solid modeling, FEA • Circuit design, SPICE, VHDL

4. Solving the Problem • Modeling principles for developing a logistics reference model: • Observability • Minimum inferred structure

5. Warehouse Resources Equipment Solving the Problem Key (Observable) Warehouse Elements Entities: Equipment Labor Labor Space Customer Goods Orders Goods Orders Customer Orders Filled Activities:changes to entities’ states

6. Solving the Problem What CAN’T be observed? Decision-making!

7. Solving the Problem Hypothetical models of decision-making • Make a “theory” of decision making • Make it as simple as possible, consistent with observed effects of decision-making, but no simpler • Minimum inferred structure This does not require designing the control system.

8. Receiving Transportation Storage Fast picking Sortation Packing Shipping Value adding services Solving the Problem Organizing Principle #1 • Warehousing resources and activities are organized by departments • Generic set of department types (or classes)

9. Solving the Problem Generic Organization of Resources DepartmentClasses Resource Types EquipmentClasses LaborClass SpaceClass ProductClass OrderClass DepartmentSet EquipmentInstances Employees SpaceInstances ProductInstances OrderInstances Resource Instances DepartmentInstances

10. Solving the Problem Object Models for Resources • Trust me, it’s straightforward • Even if it’s not unique

11. 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 #2 • Activities are organized into department-specific tasks • Generic set of task types (or classes)

12. Solving the Problem Organizing Principle #3 • Tasks correspond to flow in a functional network • Handling unit conversions • Processing options • Total workload

13. Move Retrieve Store Get Put Count Weigh Measure Scan Communicate Solving the Problem Organizing Principle #4 • Warehousing tasks are composed from fundamental warehouse operations • Generic set of operation types (or classes)

14. Solving the Problem Operation Reference Model • The associated operations reference model is simply: • do opn-IDusing {res_ID}to {handling_unit_ID}from origin_loc_IDto dest_loc_ID • where: • opn-ID indicates what operation type to perform • {res_ID} indicates which resource(s) to use • {handling_unit_ID} indicates what is to be operated on, i.e., a container or goods ID • origin_loc_ID indicates the starting location • dest_loc_ID indicates the ending location

15. Solving the Problem Assertion • The (time stamped) log of operations reports the complete state trajectory of the warehouse

16. Solving the Problem Generic Organization of Operations TaskClasses Operation Types Get/Put Store/Retrieve Move Count/Weigh/Scan/Measure SpecificTask Set Transactions Transactions Transactions Transactions Operation Instances TaskInstance

17. 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 predictbehavior Why?

18. WarehouseState Data Inferred structure of warehouse decision making process External Events EventMessage EventMonitor TaskGenerator Warehouse Physical structure Timer Operation(command) OperationManager Resources Solving the Problem Organizing Principle #5 • Warehousing tasks/operations are event driven This is a THEORY, not a model of any specific WMS

19. 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

20. Solving the Problem Location Assignment Decisions • Truck to dock • Product family to zone • Goods to/from storage location • Order to accumulation lane

21. Solving the Problem Grouping/Partitioning Decisions • Products to families • Locations to zones • Orders to waves • Lines to zones/pickers

22. Solving the Problem Sequencing/Routing Decisions • Transport routing • Pick sequencing/routing • Retrieval sequencing • Storage/retrieval interleaving

23. 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?