1.2 Problems Being Addressed

   The DAIS API is intended for transfer of process data on subscription basis as indicated in Figure 1-1 and Figure 1-2. Process data consists of quality tagged and time stamped scalar values. The API is intended to efficiently transfer large amounts of data simultaneously to many clients (subscribers). Clients and servers involved in data exchange can be of many kinds (for example, HMI or management systems as indicated in Figure 1-1). A client may also appear as a server (for example, aggregating data from other servers or performing calculations as indicated in Figure 1-3). This creates hierarchical structures of DAIS servers.

   Figure 1-3 Using DAIS as interface between multiple servers

    As an example the servers in the leftmost layer in Figure 1-3 might be OPC compliant RTUs (or IEDs), next right might be communication front ends, and the rightmost server may provide both telemetered and estimated data.

   The DAIS API is intended to be used for a wide range of industrial processes. For example:

• power transmission

• power generation

• power distribution

• water and sewage management• oil and gas

• district heating

• pulp and paper

• measurement data access

• alarms & events access

• food manufacturing

The kinds of data that can be reached through the DAIS API are:

   This data is typically available from hardware units in the process (for example, RTUs, PLCs, distributed controllers) or other control centers (for example, SCADA systems). Refined or calculated data, parameters, and alarms & events might also come from applications (for example, custom calculations, state estimation, optimization) in SCADA or Management systems. These data might be provided through the DAIS API as well.