What is a warehouse management system (WMS)? A guide for UK suppliers

A warehouse management system is the software that controls the work inside a warehouse. Wikipedia describes it as "a set of policies and processes intended to organise the work of a warehouse or distribution centre".

GS1 uses the term at both ends of a retail delivery in its Logistic Label Guideline. For the shipper: "SSCC numbers should be generated out of the logistic management system, e.g. the warehouse management system (WMS) or ERP." For the receiver: "Each warehouse should have a warehouse management system to support the receiving process".

What does a WMS do with a customer's order?

It turns the order into labelled pallets on a vehicle, and a despatch advice that describes them. The steps below are our summary, from the supplier's side.

1. The order is released to the warehouse. The customer's purchase order, received by EDI or otherwise, is recorded in your ERP as a sales order, and the work to fulfil it passes to the warehouse.
2. The stock is already in a known place. Goods received earlier were checked in and put away to a location the WMS records, so it knows where to send the picker.
3. The WMS directs the pick. It tells the warehouse team what to pick, and from where, against the order.
4. The goods are packed and each pallet is labelled. Each pallet gets an SSCC label. The SSCC can be generated from the WMS or ERP under the shipper's own GS1 Company Prefix: yours, or your 3PL's if it despatches for you.
5. The pallets are loaded and the despatch advice is sent. The ASN lists each pallet's SSCC and what is on it, built from what was actually loaded.
6. The retailer's WMS receives against it. At the customer's distribution centre, the ASN is already in their system. Goods-in scans each SSCC, and where the retailer accepts the scan, the stock is added without a hand count.

Steps 1 to 5 happen in your warehouse, or your 3PL's. Step 6 happens in your customer's. EDI carries the order in at step 1 and the despatch advice out at step 5.

Where does the ASN (despatch advice) come from?

From the loading bay. The despatch advice describes what was actually despatched, so it is built once the pick and the load are final.

GS1 defines the despatch advice (DESADV), often called the ASN, as "A message specifying details for goods despatched or ready for despatch under agreed conditions." Its guideline ties the message to the load: "Only loaded pallets should be scanned. This ensures correct delivery information for despatch advice / ASN and transport documents." And it sets the timing: "The Despatch Advice / ASN should be sent upon staging / loading of the goods, in order to maximise the chance that the information matches the actual shipment."

Retailers add their own rules. The Ocado Supplier Manual (September 2024) says the ASN "must not be sent until the actual loading procedure has been completed and no later than twenty minutes after the delivery has been shipped."

That is why the WMS is the natural source. It holds the pick and load confirmations the message needs. The Transalis ASN guide covers what the message contains and what four published UK sources say about when it is due.

Who creates the SSCC pallet label?

The shipper: you, or your 3PL if it despatches for you. An SSCC (Serial Shipping Container Code) is GS1's number for one logistic unit, "for example a case, pallet or parcel." GS1's guideline says "The shipper should use its own GS1 Company Prefix to generate the SSCC." The shipper "may be the supplier or a logistic service provider (LSP) acting on behalf of the supplier."

One of the label types the guideline describes is the picked pallet label: "A picked pallet label is printed and applied at the time the pallet (logistic unit) is picked for a customer". The SSCC on that label can be generated from the WMS or ERP, and the ASN carries the same number: "The Despatch Advice / ASN should specify for each logistic unit the SSCC and the contained trade items." The SSCC guide covers the number's structure and the label rules.

What happens at the retailer's goods-in?

The retailer's own WMS takes over. GS1's guideline sets out the receiver's side: "The Despatch Advice / ASN should be received and processed into the receivers' system before the goods arrive." Then: "When the SSCC is scanned it should match the information in the Despatch Advice / ASN, and the received amount should be automatically added to the Warehouse system and update the stock level." Whether the scan alone is accepted, or the pallets are also checked, depends on the agreement between supplier and receiver.

The two sides meet through the ASN and the label. Your WMS or ERP can write both, and your customer's WMS reads them.

UK goods-in teams work to booked slots, and the ASN guide describes how retailers use the ASN for that job: "Booking in: the ASN lets the goods-in team schedule a delivery slot in advance and allocate the right dock door and headcount before the vehicle turns up". The time from order to delivery is your lead time, and whether the delivery arrived on the due date and in the quantity ordered is what OTIF records.

WMS vs ERP: what is the difference?

The ERP is the whole business's record. The WMS runs the work inside the warehouse. The Transalis ERP guide puts the ERP side in one line: "For a UK supplier, it is where a customer's order is recorded as a sales order, and where despatch and the invoice are run from it."

The two share data. TechTarget describes the WMS updating "the inventory management module in the ERP system to ensure it has the latest information." A WMS can be its own product or part of the ERP. As Wikipedia puts it, "A WMS may be a standalone product, or can be a module or category of modules within a larger Enterprise Resource Planning (ERP) system". Either way, the split of jobs holds.

How does EDI connect to a WMS?

EDI is "the automated exchange of business documents between companies, computer to computer, in a standard electronic format," as the Transalis EDI guide defines it.

The web EDI guide draws the line: "With web EDI a person reads each order and keys each invoice, while integrated EDI connects an ERP, accounting or warehouse system so documents flow without rekeying." One Transalis case study, a toy manufacturer, puts it in a line: "Linking a warehouse system directly to an EDI data feed removes the need for manual order processing".

If a 3PL runs your warehouse, its WMS does the picking, and the despatch advice still goes to your customer. A Transalis guide on EDI for 3PLs describes one such set-up: "Once the 3PL prepared an order, an ASN was sent to the retailer, providing transparency and tracking details."

EDI does not replace the warehouse system. It feeds it.

Do you need a WMS to send ASNs to a retailer?

No. The ASN guide sets out three routes. The ASN can be generated "from the same order data already held in the trading connection". It can be triggered from an ERP or WMS, where "picking and packing confirmations trigger the ASN automatically, with SSCC labels generated and applied to pallets as part of the same process". Or, "for suppliers who are not ready to connect their own systems, an ASN can be completed and sent through a web form". The retail EDI requirements playbook describes Web EDI "with automated SSCC pallet-label printing built in".

The difference is who confirms the load. Without a connected WMS, a person confirms the quantities and despatch details. With one, the pick and pack confirmations do it.

How Transalis connects EDI to your warehouse system

Transalis is a managed outcomes provider for B2B integration, EDI and eInvoicing. On the EDI page, Integrated EDI is "EDI wired directly into your ERP, accounting or warehouse system." The same page says "Transalis connects to your ERP, marketplace or warehouse system through a single integration point."

The ASN guide adds that "Transalis OpenEDI™ supports all three of these routes on the same connection, so a supplier can start with a browser based service and move to full ERP integration later". The integration network page describes the model: "we plug into your ERP, accounting or ecommerce system through a connector that already exists". The warehouse keeps running the warehouse. Transalis carries the orders in and the despatch advices out.

Book a 30-minute call with a Transalis retail supply chain specialist to walk through EDI between your warehouse system and your retail customers.