These chapters explain how the most commonly used entities in OPC Unified Architecture, such as servers, nodes, and attributes, are identified in the application code.

Note: Some entities in OPC Unified Architecture are identified by URIs and URLs. .NET Framework has a System.Uri class that provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI. It is generally recommended that programs use this class for URI manipulation internally, instead of working with plain strings containing URIs. In OPC Unified Architecture, however, the URIs and URLs are used in such a way that they do not always have to fully conform to the specifications. For this reason, URI and URL arguments and properties in OPC Data Client-UA are also strings and not System.Uri (and are consistently named so they contain “UriString” or “UrlString”).