This namespace contains classes for OPC Unified Architecture (OPC-UA) discovery.

Classes

	Class	Description
	UAApplicationDescription	Contains OPC UA application description.
	UAApplicationDiscoveryQuery	Specifies an OPC UA application discovery query.
	UAApplicationElement	Contains OPC UA application registration information.
	UAApplicationTypesUtilities	Contains utility methods for the UAApplicationTypes class.
	UADiscoveryElement	Contains information gathered about an OPC application (typically, an OPC-UA server) or an endpoint.
	UADiscoveryElementCollection	A collection of application elements (servers, UADiscoveryElement).
	UADiscoveryQuery	Specifies a discovery query in OPC Unified Architecture.
	UAGlobalApplicationDiscoveryQuery	An OPC UA discovery query for searching the applications globally in the administrative domain.
	UALdsDiscoveryQuery	Specifies an OPC UA discovery query performed using a LDS or LDS-ME service.
	UALocalApplicationDiscoveryQuery	An OPC UA discovery query for applications on the specified discovery host or discovery endpoints.
	UALocalEndpointDiscoveryQuery	An OPC UA discovery query for local endpoints.
	UANetworkServerDiscoveryQuery	An OPC UA discovery query for applications on a network.
	UAQueryApplicationsFilter	A filter used to find servers that meet the specified criteria.
	UAServerOnNetwork	A DNS service record for OPC Unified Architecture (OPC UA).

Interfaces

	Interface	Description
	IUAReadOnlyApplicationElement	Contains read-only OPC UA application registration information.
	IUAReadOnlyDiscoveryElement	Contains read-only information gathered about an OPC application (typically, an OPC-UA server) or an endpoint.

Enumerations

	Enumeration	Description
	UAApplicationTypes	The type of application.

Remarks

OPC UA Discovery allows OPC Data Client to find available OPC UA servers, and determine how to make connections to them. There are several approaches to discovery, and they can be combined together to achieve the desired functionality. Clients and servers can be on the same host, on different hosts in the same subnet, or even on completely different locations in an administrative domain.

OPC Data Client provides following kinds of discovery:

OPC UA Local Discovery. Obtains information about the servers on a specified host using OPC UA Local Discovery Server (LDS) running on that host.
OPC UA Network Discovery. Also known as MulticastSubnet Discovery. The information is obtained from a Local Discovery Server with Multicast Extensions (LDS-ME), which uses the mDNS protocol to exchange the information about OPC UA servers with other LDS-ME-s on the network (or multiple networks).
OPC UA Global Discovery. Obtains information about applications available in an administrative domain by interrogating an OPC UA Global Discovery Server (GDS).

It is also possible to access the discovery functionality in a common way, using Generalized OPC UA Discovery.

Flattened and unflattened results

By default, the results (the application element collection) of many of the methods described in this chapter are returned flattened. This means that a single OPC UA application may appear multiple times in the resulting collection, and each time it will have precisely one DiscoveryUriString associated with it.

Alternatively, you can use method overloads with the additional 'flat' argument, and set it true, in order to receive unflattened result. In this case, each OPC UA application will be contained just once in the resulting collection, but it may have one or more discovery URL in its DiscoveryUriStrings property. In this case, do not use the DiscoveryUriString property, because it will contain an empty string if the application has more than one discovery URL.

Alarms & Conditions

Please refer to the “Discovering OPC UA Servers” chapter under “Imperative Programming Model for OPC Data (Class and UA)” for all necessary information. OPC Unified Architecture, as the name suggests, allows to treat multiple functionality areas commonly, and the same OPC Servers that provide Data Access functionality are (or can be) also Alarms & Conditions servers.

Reference

OpcLabs.EasyOpcUA Assembly