OPC UA is an open and royalty free set of standards designed as a universal communication protocol. While there are numerous communication solutions available, OPC UA has key advantages:
A state of art security model (see OPC 10000-2).
A fault tolerant communication protocol.
An information modelling framework that allows application developers to represent their data in a way that makes sense to them.
OPC UA has a broad scope which delivers for economies of scale for application developers. This means that a larger number of high-quality applications at a reasonable cost are available. When combined with semantic models such as IEC61131-3, OPC UA makes it easier for end users to access data via generic commercial applications.
The OPC UA model is scalable from small devices to ERP systems. OPC UA Servers process information locally and then provides that data in a consistent format to any application requesting data - ERP, MES, PMS, Maintenance Systems, HMI, Smartphone or a standard Browser, for examples. For a more complete overview see OPC 10000-1.