New acronyms regularly spring up in logistics, but there are three that are important to note: WMS, WES and WCS. But how are these systems actually defined? Why are they so essential and how do they differ? Are there standard definitions for the solutions behind them?
In this blog, we’ll provide a clear picture, clarify the terminology and explain the roots of these solutions. Read on to expand your understanding of software architecture and avoid an expensive pitfall in your company’s next project. Lets dive right in!
Where do the terms and acronyms come from?
To be clear, with WMS (warehouse management system), WES (warehouse execution system) and WCS (warehouse control system), we are not dealing with system classes arising from standards, but from terms that have arisen from the industry and the market. That’s why the boundaries and scope of functions of each of these systems are not always clear-cut.
Simplified system hierarchy with the main tasks of a WMS/WES/WCS:
Warehouse Management System - WMS
- Inventory Management
- Order management
- Reporting
Warehouse Execution System - WES
- Order control
- Workflows
- Resource Coordination
Warehouse Control System - WCS
- Device control
- Material flow
- Scanning & Sorting
Why do these terms get confused so often?
Currently, there are no standards that delineate the functions and interfaces across all the systems. There are isolated approaches for areas, but no consistent descriptions.
Examples include:
ISA-95 (IEC 62264):
This set of standards covers the information exchange between an ERP system for MES architectures (manufacturing execution systems).
| ISA 95 Level | Typical association |
|---|---|
| Level 4 | ERP |
| Level 3 | WMS / WES |
| Level 2 | WCS / SCADA |
| Level 1–0 | PLC / sensors |
VDI 3601:
These guidelines describe the tasks and performance areas of a warehouse management system and address the core and additional functions in detail.
MESA/MOM (Manufacturing Enterprise Solutions Association or Manufacturing Operations Management Systems):
Describes executing systems as an event- and resource-oriented orchestration layer.
VDI 4499:
Contains the central principles for the end-to-end planning, simulation and optimization of a “digital factory”. It is an architecture framework for interfaces that are maintainable and scalable.
Because the standards go into different depths in establishing definitions, in reality, functions and processes cannot always be uniquely assigned to just one system and therefore must be clarified in detail within a project. As initially explained, the reason is because the terms WMS/WES/WCS are system categories driven by the market and not centrally standardized levels. Over the years, the meanings have changed, and functions and responsibilities can overlap in the systems.
The same applies to the definitions for the interfaces between the systems. Neither the ISO, IEC nor the VDI have published standards clearly defining these system classes and authoritatively describing their data objects, message flows or responsibilities. That’s why interfaces always depend on the supplier and must be defined within a project. Nonetheless, let’s start with a fundamental explanation of what the systems are typically responsible for in a warehouse and what the system architecture would look like. Based on this system architecture, we will see what each system does and what information is exchanged between the systems.
Warehouse Management Systems (WMS)
The WMS is a system that takes care of the logical and logistical control of a warehouse and
- manages stocks,
- controls all storage-related business processes,
- and ensures that customer orders are efficiently and correctly processed.
Simultaneously, it links the existing ERP system and the operational aspects of the warehouse.
The focus of the WMS
Its focus is on process-oriented planning and optimization in the warehouse:
- Stock management (quantities, locations, status)
- Goods-in, storage strategies, relocations
- Picking strategies (e.g.batch, multi-order)
- Shipping preparation and order prioritization
There is less focus on physical movements and more on the logic of “what, when, who, and how.”
Tasks of the WMS
The WMS acts on a level that is tactical and operational and:
- translates customer orders into executable warehouse tasks
- defines strategies and priorities
- optimizes the use of storage locations and resources
However, it does not make any control decisions in seconds for the automated part of a warehouse, because a WMS is decoupled from the actual execution. Nevertheless, it retains data and therefore needs good data consistency and availability.
Relation to higher-level and subordinate systems:
Between the WMS and the higher-level ERP system:
The following information is typically transmitted from the ERP system to the WMS:
- Customer orders / delivery orders (goods-out)
- Purchase orders (goods-in)
- Shipping and transport data
- Master data (customer, supplier, item, etc.)
- Labels (e.g. shipping label)
The WMS typically transmits the following information to an ERP system:
- Stock information (aggregate stocks, stock changes, inventory information)
- Goods-in and goods-out confirmations
- Shipping and transport data
- Order updates if relevant to business (e.g. to give a customer the current order status)
Between the WMS and the subordinate WES:
A WMS typically transmits the following information to a WES:
- Order data (goods-in, goods-out)
- Master data relevant to the warehouse (e.g. item master data)
- Process procedures (strategies, priorities, etc.)
- Labels (e.g. shipping labels)
A WES typically transmits the following information to the WMS:
- Status and progress messages
- Errors / deviations
- Replenishment requests
- Inventory and stock updates
Definitions from theory
The VDI 3601 defines what a WMS is and what it must be able to do. It defines its tasks and functions and classifies the WMS as the central control and optimization system in intralogistics. This pertains to the functions and not how it is technically achieved.
ISA-95 (level 3) states that systems are required for the operational control of business requirements from an ERP system, which these systems carry out and monitor. It does not explicitly mention the WMS but defines the functional level (level 3) that can be handled by a WMS.
Warehouse execution system (WES)
The WES is the orchestrating level between the WMS and the automation technologies. It translates warehouse tasks into optimally sequenced, resource-efficient processes, and synchronizes various subsystems in real time. This is the newest of the three system categories. Functional precursors arose at the beginning of the 2000s, but the term was only established on the market after 2012.
The focus of the WES
In WES systems, the focus is on the dynamic control of processes and optimizations in ongoing operation:
- Order release and order sequencing in real time
- Synchronization of manual and automated processes
- Control of resources (e.g. work stations, shuttles, robots)
- Management of bottlenecks and continuous adjustment of priorities
The goal is clear: Ensuring and raising the maximal performance (throughput, punctuality) of the overall system.
Tasks of the WES
The WES operates on a level that is highly operational and decision-heavy:
- to continuously make decisions pertaining to optimization based on the current system status
- to react to errors, dynamically adapting processes
- to work in seconds and minutes
- but has no long term stock management
Demarcation between higher-level and subordinate systems:
Between the WES and the higher-level WMS:
The following information is typically exchanged between a WES and a WMS:
- Order data (goods-in, goods-out)
- Master data relevant to the warehouse (e.g. item master data)
- Process procedures (strategies, priorities, etc.)
- Labels (e.g. shipping label)
An existing WES typically transmits the following information to the WMS:
- Status and progress messages
- Errors / deviations
- Replenishment requests
- Inventory and stock updates
Between the WES and the subordinate WCS:
An existing WES typically transmits the following information to the WCS:
- Transport orders
- Order prioritization / sequencing
- Material flow decisions (e.g. about routing)
A WES typically receives the following information from an existing WCS:
- Status and progress messages
- Errors / deviations
- Information on system status and workload
- Confirmation when a task is physically executed
- Data transmissions of check data (e.g. weight, barcodes)
- Labels (e.g. shipping labels) if automatically applied
The detailed technical execution is left to the subordinate systems, such as a WCS.
Functional differences
The market has established definitions for the scope of functions of a WES. However, these usually describe functionalities and not entire systems. WES functions are also reflected in MESA’s (Manufacturing Enterprise Solutions Association) definitions of MES (Manufacturing Execution System) or MOM (Manufacturing Operations Management System), where a WES would be equivalent to level 3 in ISA-95. The WES is not explicitly mentioned here, instead, the functional level (level 3) is defined, which are functions that a WES can perform.
Warehouse control systems (WCS)
The WCS functions at the level of technical control, directly controlling the physical movement of goods in the system The WCS connects software systems with the automation technologies (PLC) ensuring that all transport and control commands are executed correctly. The results or return messages are forwarded to the higher-level system (e.g. WES or WMS).
The focus of the WCS
The focus of a WCS is on real-time material flow and system control:
- Routing objects on various types of conveying equipment
- Connecting to further subsystems such as shuttle systems or robots
- Direct communication with the PLC
- Responding to return messages from sensors, scanners and other actors
The WCS is therefore very technically oriented, with a focus on stability and reaction time.
Tasks of the WCS
Since the WCS works directly at an operational, technical level in real time, it must be able to:
- respond in milliseconds to seconds
- fulfill high requirements for availability and be robust
- execute set movement logic without a separate process strategy
- does not have to carry out separate optimizations of overall processes
Demarcation between higher-level and subordinate systems:
Between the WCS and the higher-level WES:
A WES is typically responsible for transmitting the following information to the WCS:
- Transport orders
- Order prioritization / sequencing
- Material flow decisions (e.g. about routing)
A WES typically receives the following information from an existing WCS:
- Status and progress messages
- Errors / deviations
- Information on system status and workload
- Confirmation when a task is physically executed
- Data transmissions of check data (e.g. weight, barcodes, etc.)
- Labels (e.g. shipping label) if automatically applied
Between the WCS and the subordinate PLC or mechanical components:
Direct control of the hardware
→ Communication with conveyor system, sensors, robotics
Functional demarcation
On the control level, there are established technologies for systems to communicate with each other. However, the content of the interfaces always depends on the respective implementation. For this reason, the WCS can only be roughly categorized in the established standards. As the WCS is responsible for technical control and deterministic execution , it can be classified as level 2 in ISA-95. This means that the processes in the WCS are based on concrete logical rules and that processes are always predictable and optimizable.
When is each system needed?
There is no pat answer to the question of which system is the right one for you and your project. The right software solution depends on many different factors such as degree of automation, scope, technologies and much more. Let’s therefore take a look at different scenarios for warehouses. Depending on the situation, the answer will be different.
1) Manual warehouse
2) Semi-automated warehouse
3) Highly automated warehouse
Which system handles which functions?
Maybe you’re wondering whether these three systems must always be introduced separately. The answer is a clear “no”. Many WMS or WCS solutions on the market cover the functions of a WES solution. There are also a few solutions on the market that unite the WMS/WES/WCS functionalities within one product, so that there is no delineation.
The challenge, however, is when the systems of different suppliers must be combined in one system.
Regardless of separate or combined solutions, what must be very clearly defined is which system is the responsibility of which supplier. The logistical and technical responsibility must be assumed and also clearly demarcated. It’s important to eliminate overlapping responsibilities, which would lead to unclarity in operations.
For example, if the WMS were to transmit a priority for a customer order to the WES, the WES must account for this previous priority in the execution planning and the WCS must adapt the machine control and routing accordingly.
If one of the systems should ignore or overwrite the requirements or decisions of the other system, it can lead to unwanted behavior in the system, for example, insufficient capacity, idle time at the work stations or similar. For each decision, only one system can be responsible. The other systems may only deliver the information or execute the decisions.
If this is not clearly defined, it slows down finding a solution. This must be avoided at all times because it leads to high costs and massive disruptions in deliveries. Having responsibilities clearly defined is thus an important point for the long term successful operation of a warehouse.
Logistical responsibilities
From the logistical perspective, responsibilities can be divided up as follows:
Responsibility for the entire warehouse
Responsibility for the executing part (e.g. automation, process execution)
Responsibility for the system performance for parts of the automated systems
Technical responsibilities
From the technical perspective, responsibilities can be divided up as follows:
Responsibility for all warehouse processes
Responsibility for process planning and orchestration
Responsibility for the execution and implementation of automation technology
Checklist:
So what should you pay attention to when selecting the system? Here is a short checklist with questions that will help you make the right decisions:
- Would following a "single source supplier" strategy make sense to avoid responsibility, functional boundary and interface issues, and to reduce coordination and thus costs?
- Is there a common understanding of the roles and responsibilities of the systems?
- Is a control system needed? And is it (e.g. WCS) cleanly decoupled from the business logic?
- Does the complexity of the system and process landscape require an orchestration layer in the form of a WES?
To address these questions, we recommend creating a responsibility matrix that clarifies:
- who decides on priorities
- who orchestrates the resources
- who controls which machines in real time (PLC or own machine-related software systems)
If you answer these questions and are able to clarify the responsibilities, then the following situations cannot arise:
- a WMS takes over WES tasks “because it can”
- a WCS includes business logic “because it was faster and easier”
- a WES is introduced without adjusting the roles and responsibilities of the other systems
- interfaces are mistakenly used to shift responsibilities
Conclusion:
Currently, there is no one standard for WMS, WES or WCS. However, there is a set of established reference works to functionally differentiate the systems from each other.
Since there is a lot of room for interpretation, there are always overlaps of functionalities between systems. However, you should always avoid integrating functionalities into systems where they don’t belong.
The following table gives an overview of some functions and the systems in which they are typically classified.
Legend:
✅ = Function should be mapped here
⚠️ = Function will be partially mapped here
❌ = Function should not be handled by this system
| Functionality | WMS | WES | WCS |
|---|---|---|---|
| Order management (rough planning) | ✅ | ⚠️ | ❌ |
| Detail scheduling / sequencing | ⚠️ | ✅ | ❌ |
| Order processing (real time) | ❌ | ✅ | ⚠️ |
| Stock management / inventory authority | ✅ | ❌ | ❌ |
| Material flow system (logical) | ⚠️ | ✅ | ⚠️ |
| Material flow system (physical / real time) | ❌ | ⚠️ | ✅ |
| Resource management (system, personnel) | ⚠️ | ✅ | ⚠️ |
| Monitoring / status tracking | ✅ | ✅ | ✅ |
| Real time data processing | ❌ | ✅ | ✅ |
| Incident management (deviations) | ⚠️ | ✅ | ✅ |
| Optimization (strategic) | ✅ | ❌ | ❌ |
| Optimization (operational / real time) | ❌ | ✅ | ⚠️ |
| Tracking and traceability | ✅ | ✅ | ⚠️ |
| Quality checks (processes) | ⚠️ | ✅ | ⚠️ |
| Data acquisition (store floor) | ❌ | ✅ | ✅ |
| Document / process logic | ✅ | ✅ | ❌ |
If you keep these points in mind, you can clarify the responsibilities of the systems and avoid long-term discussions and expensive change requests during system changes. In addition, you avoid redundant functionalities and data storage and thus eliminate constant reconciliation between the systems. Hopefully, our take on defining these systems will help you to avoid playing responsibility ping-pong with suppliers.
If you would like to bring more clarity and accountability to your systems, please feel free to contact our experts.
The authors of this article:
Mario Berger
Product Marketing Manager
Is Product Communication Manager at KNAPP AG in the Product Management department. As an interface between technology and communication, he develops content around software solutions and digital systems for intralogistics and ensures that complex relationships are conveyed in an understandable and target group-oriented manner.
Nina Bäuchler
Online Marketing Managerin
In our blog, Nina deals with digital trends, content strategy and the use of artificial intelligence in logistics. Her focus is on classifying technological developments and making their significance tangible for companies, processes and communication.
