Application programming interfaces in the IIoT

Application programming interfaces (APIs) have been used for many years to enable computer programs to exchange information. A common example is websites, where one site will use data from another site, such as a LinkedIn or Twitter feed. However, they have not been commonly used in manufacturing systems. As more and more systems are connected through Industry 4.0 initiatives, APIs will be used more commonly. But what exactly are APIs? And how can they be used for smart manufacturing and Industrial Internet of Things (IIoT) applications?

What is an API?

An API is a set of definitions and protocols used to create and integrate different application software, so that they can communicate with each other. It can be seen as an agreement between an information provider and a consumer. The consumer will make a call or request (request information) and the supplier will provide a response (give information). The API defines how the question should be worded in order to get the desired answer. The API also defines how the response will be provided.

API types

There are many APIs that can be used, but RESTful (Representational State Transfer) or RESTful APIs are the most common. It is a defined structure using common web protocols and data formats. When a consumer application wants information, it makes an HTTP (Hypertext Transport Protocol) request to the provider, which responds with the formatted data. Like APIs, there are many data formats that can be used, but JavaScript Object Notation (JSON) is the most popular in most applications due to its simple data structure. It should be noted that although it has Java in its name, JSON is language independent, taking advantage of the way data is put together.

Another API sometimes used is a Simple Object Access Protocol (SOAP) API. Unlike REST, SOAP is much more structured and little needs to be known about the format of the request and response. When using SOAP, the information provider uses a Web Services Description Language (WSDL) file to facilitate data exchange. While it might sound easier, it has specific requirements that often make it slower and heavier.


In the context of Industry 4.0, many other manufacturing systems will be connected using APIs. For example, a supervisory control and data acquisition system (SCADA) will connect directly to a computerized maintenance management system (CMMS) for the creation and management of work orders. Quality information, such as instrument calibration data, will be logged with process data. Data from disparate systems will be easily visualized from a common platform.

A typical scenario would include a line operator and a downtime event. Traditionally, when the event occurs, the operator will attempt to resolve the problem. If this requires a maintenance person, contact is made by other means, such as a radio or telephone. The technician will arrive on the line, perform the repair, and the line will resume operation. Only downtime and line start time events are captured in real time. Other events (such as work order, shipping, line arrival) would not be known.

Using an API, the operator can generate a work order or a work order request, directly from the control system. The maintenance person will be dispatched through the maintenance system. The technician will connect to the control system, perform the repair, and then update the work order status on the line. In this case, the build, ship, and finish times of the work order are all captured along with the downtime and start-up events.

APIs are not limited to software systems. As more data becomes available from peripheral devices, such as instruments and sensors, the hardware used to connect these devices will use APIs. For example, using a similar scenario described above, a programmable logic controller (PLC) controlling a remote asset, such as a compressor, will use a PLC to send the request directly to the work control system based on conditions and states of functioning. The advantage is that APIs are used to connect disparate devices and systems so that they can operate more efficiently.

Moving forward

In the future, there will be an increased need to support the use of APIs on many devices. It will be essential that people who have not used them, such as engineers and control systems technicians, can make requests and analyze the responses. Knowledge of REST and JSON will be required for these roles. Similarly, more hardware will need to support this feature in order to be considered in smart manufacturing applications.

Although I mentioned manufacturing systems and devices, there are many other uses for APIs. Industries that have remote assets, like oil, gas, or water, will use APIs to obtain geolocation data. Weather data could be captured along with location data to display it in context. In the agricultural industry, APIs are used to display information such as commodity prices. It may be beneficial to consider including some of these in a manufacturing environment.

As managers seek to bridge what is known as the skills gap, they will need to consider these abilities when adding or replacing roles in a factory. It is strongly recommended that managers also learn these skills. When Industry 4.0 initiatives are planned and executed, the capabilities of new systems and equipment should be seen as part of the technology stack.

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