The various kinds of OPC UA discovery can be generalized into just one method, Discover. This method is given a discovery query argument (of UADiscoveryQuery type) that tells it the requirements for the discovery. The specific kinds of OPC UA discovery described earlier are, in fact, implemented by constructing the discovery query appropriately, and then calling the Discover method.

The UADiscoveryQuery type is an abstract class which is at the root of a structured class hierarchy, with several concrete subclasses:

• UAGlobalApplicationDiscoveryQuery is for searching the applications globally in the administrative domain. With this query, you need to specify the GDS endpoint, and optionally a filter (UAQueryServerFilter), used to find servers that meet the specified criteria.
• UALocalApplicationDiscoveryQuery is used when you know the LDS endpoints, and want to perform discovery on these endpoints (usually in parallel). This is a specialized kind of local discovery.
• UALocalApplicationDiscoveryQuery is for finding applications local to a specified host.
• UANetworkServerDiscoveryQuery is for finding servers on a multicast subnet (or more connected subnets) using LDS-ME (Local Discovery Server with Multicast Extensions).

This generalized discovery mechanism allows for flexibility both on the component and developer sides, and possible future expansion with other kinds of discovery, without a need to introduce new methods into the IEasyUAClient interface.