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OPC Unified Architecture Introduction

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The existing OPC COM based specifications - called OPC Classic - have served the OPC Community well over the past 10 years, but as technology moves on so must the interoperability standards. Feedback from thousands of applications worldwide has provided a lot of experience that now can be used as a foundation for a new approach to systems interoperability.

This topic contains the following sections:

The main factors that influenced the OPC Foundation decision to propose a new architecture are summarized below:

  • Microsoft has deemphasized COM in favor of cross-platform capable Web Services and SOA (Service Oriented Architecture)

  • OPC Vendors want a single set of services to expose the OPC data models (DA, A&E, HDA ...)

  • OPC Vendors want to implement OPC on non-Microsoft operating systems, including embedded devices

  • Other collaborating organizations need a reliable, efficient way to move higher level structured data

OPC Unified Architecture is a set of specifications applicable to manufacturing software in application areas such as Field Devices, Control Systems, Manufacturing Execution Systems and Enterprise Resource Planning Systems. These systems are intended to exchange information and to use command and control for industrial processes. OPC Unified Architecture defines a common infrastructure model to facilitate this information exchange.

In January’2004 the OPC Foundation tasked a working group to create a new architecture that would take OPC to the forefront of technology and provide an interoperability framework that would be viable for the next 10 years and beyond. The first parts of this new "Unified Architecture" were released in June’2006.

Structure of the specifications collection

This section contains the following subsections:

The OPC Unified Architecture (OPC-UA) is described in a layered set of specifications broken into Parts. It is purposely described in abstract terms and in later parts married to existing technology on which software can be built. This layering is on purpose and helps isolate changes in OPC Unified Architecture from changes in the technology used to implement it. The structure and depth of material to absorb in learning is harder than the OPC COM Specifications. It is best to read the introductory articles and in-depth presentations before tackling the OPC Unified Architecture Specifications.

The OPC Unified Architecture specification is organized as a multi-part document combined in the following sets:

  • Core Specification Parts

  • Access Type Specification Parts

The first seven parts specify the core capabilities of the OPC Unified Architecture. These core capabilities define the structure of the Address Space and the services that operate on it. Parts 8 through 11 apply these core capabilities to specific models of data access previously addressed by separate OPC COM specifications, such as Data Access (DA), Alarms and Events (A&E) and Historical Data Access (HDA). Part 12 describes Discovery mechanisms for the OPC Unified Architecture. Readers are encouraged to read Parts 1 through 5 of the core specifications before reading Parts 8 through 12. For example, a reader interested in UA Data Access should read Parts 1 through 5 and 8. References in Part 8 may direct the reader to other parts of the specifications.

Core Specification Parts

This set contains the following specifications:

  • Part 1 – Overview and Concepts: presents the concepts and overview of OPC Unified Architecture.

  • Part 2 – Security Model: describes the model for securing interactions between OPC Unified Architecture Clients and Servers.

  • Part 3 – Address Space Model: describes the contents and structure of the Server Address Space.

  • Part 4 – Services: specifies the Services provided by OPC Unified Architecture Servers.

  • Part 5 – Information Model: specifies the types and their relationships defined for OPC Unified Architecture Servers.

  • Part 6 – Mappings: specifies the transport mappings and data encodings supported by OPC Unified Architecture.

  • Part 7 – Profiles: specifies the Profiles that are available for OPC Clients and Servers. These Profiles provide groups of Services or functionality that can be used for conformance level certification. Servers and Clients will be tested against the Profiles.

Access Type Specification Parts

This set contains the following specifications:

  • Part 8 – Data Access: specifies the use of OPC Unified Architecture for data access.

  • Part 9 – Alarms and Conditions: specifies the use of OPC Unified Architecture support for access to Alarms and Conditions. The base system includes support for simple Events; this specification extends that support to include support for Alarms and Conditions.

  • Part 10 – Programs: specifies OPC Unified Architecture support for access to Programs.

  • Part 11 – Historical Access: specifies the use of OPC Unified Architecture for historical access. This access includes both historical data and historical Events.

  • Part 12 – Discovery: specifies how Discovery Servers operate in different scenarios and describes how UA Clients and Servers should interact with them. It also defines how UA - related information should be accessed using common directory service protocols such as UDDI and LDAP.

See Also