Essence of a “science” Observation Observation Categorization/classification Categorization/classification Abstraction Abstraction Symbolic representation Symbolic representation Manipulation Manipulation Prediction Prediction Fundamental Problem

Look for a reasonably small set of organizing principles Look for a reasonably small set of organizing principles Propose reference model elements Propose reference model elements Check for consistency Check for consistency Refine Refine Reference models are artifacts, not natural phenomena Solving the Problem Creating a Reference Model

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

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

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

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

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

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

Department Classes Department Set Department Instances Generic Organization of Resources Equipment Classes Labor Class Space Class Product Class Equipment Instances EmployeesSpace Instances Product Instances Resource Types Resource Instances Order Class Order Instances Solving the Problem

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

Organizing Principle #2 Receiving: Unload/receive Receiving: Unload/receive Transport: Put-away; retrieve; replenish Transport: Put-away; retrieve; replenish Pallet Storage: Pick pallet; case pick to pallet 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 Activities are organized into department- specific tasks Generic set of task types (or classes) Solving the Problem

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

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

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

Task Classes Specific Task Set Task Instance Generic Organization of Operations Get/PutStore/RetrieveMoveCount/Weigh/ Scan/Measure Transactions Operation Types Operation Instances 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 Warehousing tasks/operations are event driven Resources Warehouse Physical structure Solving the Problem Inferred structure of warehouse decision making process External Events Event Message Operation (command) Warehouse State Data Event Monitor Task Generator Operation Manager Timer This is a THEORY, not a model of any specific WMS

Bad News and Good News Bad: Task generators are specific to the warehouse design, because they are specific to a department instance! 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 Good: But there may be typical elements of task generators Solving the Problem

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

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

Sequencing/Routing Decisions Transport routing Transport routing Pick sequencing/routing Pick sequencing/routing Retrieval sequencing Retrieval sequencing Storage/retrieval interleaving 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? Solving the Problem