Overview

Requirements

See Requirements Summary

Summary

As of MVP2, the Order Queue in the product (see Order Queue Story) is based on Kanban Cards and it inherits from them limitations that introduce friction in the procurement processes. The two reported issues state:

• Users want to add quantities of items to the order queue from a card or an item multiple times, not necessarily only once per card.
• When some data conditions are not met, the system prevents the user form moving the card to the next state. The system should provide an easy override for the user to force the transition (e.g. they may have completed purchasing transactions outside the system).

The challenge is that the order queue is directly based on Kanban Cards, when a different model would be more appropriate.

Domain Model

Kanban Cards represent the flow of a fixed amount of inventory or work-in-progress in a production flow. Kanban Cards travel in Loops between stations.

The simple model is as follows:

In reality the model needs to be more sophisticated to support the flexibilty of the business.

Entity Definitions

Kanban and Loop

Kanban Card: A unit of material flow or work-in-progress in a production flow.

Loop: A single step flow of demand and fulfillment of a particular kind (materials, jobs) between a supplier station and a consumer station.

Loop Demand: The information flow communicating needs from a consumer to a supplier.

Loop Supply: The material flow that fulfills the needs of a consumer from a supplier, usually in response to a previous demand.

Station

A location in the production flow where material or work-in-progress is processed.

Supplier Station: A station that provides material or work-in-progress to a loop.

Consumer Station: A station that consumes material or work-in-progress from a loop.

Note that there may be stations that play both roles for different loops.

Ports

A port is the place where loops attach to stations.

Order Port: The connection from a Consumer Station to signal new demand in a loop.

Demand Port: The connection from a Loop to a Supplier Station to deliver a demand request.

Ship Port: The connection of a Supplier Station to a Loop to deliver fulfillment materials.

Receive Port: The connection of a Consumer Station to a Loop to receive fulfillment materials.

Items

Items are the units of processing in a Station.

Demand Item: The unit in which a Supplier Station accepts demand requests from a Loop.

Ship Item: The unit in which a Supplier Station delivers fulfillment materials to a Loop.

Order Item: The unit in which a Consumer Station signals new demand to a Loop.

Receive Item: The unit in which a Consumer Station receives fulfillment materials from a Loop.

Relationships between Kanban Cards and Items

A Kanban Card is the unit of material flow or work-in-progress in a production flow, this unit is the shared communication between stations.

Each station, depending on their processing characteristics may handle materials or work-in-progress in different units than the Kanban Card specifies.

Examples of the four ways in which a station interacts with Kanban Cards:

• A Supplier Station may accumulate Kanban Cards that are received from a Loop waiting for capacity to be available, or to batch them together due to economic or set-up reasons.
• A Supplier Station may batch Kanban Cards for shipping due to transportation capacity or economic reasons.
• A Consumer Station may accumulate Kanban Cards that are received as fulfillment from a Loop depending on their local policy for raw materials replenishment.
• A Consumer Station may not release Kanban Cards immediately after depleting them depending on their minimum raw materials policy.

To absorb these variations, Each kind of port has an associated Item kind to handle the grouping of Kanban Cards for their processing needs and policies.

In the model above, Kanban Cards are still indivisable between Items (a Card should not be in two places at once), although in a future model this may change.