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Wed, 2011-Apr-13

Industrial REST

REST is the foundation of the Web, and is increasingly relevant to enterprise settings. I hail from a somewhat different context of industrial control systems. I have been thinking of putting together a series of articles about REST within this kind of setting to share a bit of experience and to contrast various approaches.

is an architectural style that lays down a set of design constraints that are intended to create various desirable properties in an architecture. It is geared towards the architecture of the Web, but has many other applications. REST makes and excellent starting point for the development of .

SCADA systems are usually built around SCADA protocols such as , , or . Exactly what protocol is used will depend on a variety of factors such as the particular control industry we happen to be working in, preferences of particular customers, and the existing installed base.

The SCADA protocol plays the same role in a SCADA system as HTTP plays on the Web. It is pitched at about the same level, and has many similar properties. If we are to reimagine the SCADA system as a REST-compliant architecture then the SCADA protocol would be the application protocol we would have in use.

SCADA protocols have been developed over a long period of time to be typically very bandwidth-efficient and to solve specific problems well. However, we have been seeing for a long time now across our industries the transition from slow serial connections to faster ethernet. We have been seeing the transition from modem communication to broadband between distant sites. Many of the benefits of existing protocols are being eaten away as they are shoehorned into internet-based environments and are needing to respond to new security challenges and the existence of more complex intermediary components such as firewalls and proxies. We see protocols such as OPC responding by adopting SOAP over HTTP as a foundation layer and then implementing a new SCADA protocol on top of this more complex stack.

I would like to make the case for a greater understanding of REST in the industrial communications world, a new vision of how industrial communications interacts with intranet environments, and to identify some of the areas where HTTP as the main REST protocol of today is not quite up to snuff for the needs of a modern control systems world.