The OPC UA systems architecture models Clients and Servers as interacting partners. Each system may contain multiple Clients and Servers. Each Client may interact concurrently with one or more Servers, and each Server may interact concurrently with one or more Clients. This model enables Clients to access data, invoke Services, and receive Events from Servers. An application can embody both Server and Client functionalities, allowing it to exchange information with other Servers and Clients as described in 5.3.7.
Clients and Servers are described in 5.2 and 5.3. Figure 2 illustrates the architecture that includes a combined Server and Client.
