Programming with the ALE and ALEPC APIs

Event Triggers

The following sections describe the use of event triggers with the RFID Edge Server:

Overview of Event Triggers

You can define event cycle specifications (ECSpecs) and programming cycle specifications (PCSpecs) where the beginning and/or end of each cycle is triggered by external events. BEA provides an extensible mechanism for connecting sources of external events to the ALE engine.

OLE for Process Control (OPC) Trigger Driver

Object Linking and Embedding (OLE) for OPC is a series of standards specifications that define a standard set of objects, interfaces, and methods for use in process control and manufacturing automation applications to facilitate interoperability. (For more information on OPC, see http://www.opcfoundation.org.)

WebLogic RFID Edge Server includes a driver for OPC triggers. An event or programming cycle in the Edge Server can be triggered by polling for a change in an OPC item. The Edge Server communicates with the OPC service using the OPC XML-DA protocol, which is a SOAP interface to an OPC Data Access provider. The OPC XML-DA implementation is provided by a third party.

The general form of the trigger URI is:

opcpoll:itemName=item;http://hostname/location

where:

item is the name of the OPC item that the driver polls for changes.
http://hostname/location is the URL that is used to create the connection to the OPC XML-DA server.

When an event cycle or programming cycle that uses an OPC trigger is first requested (that is, when the event cycle or programming cycle is invoked using the poll or immediate method or subscribed using subscribe), the Edge Server polls the OPC XML-DA server for the current value of the specified OPC item. Afterwards, each time the value of the OPC item changes, a trigger will be delivered to the event cycle or programming cycle.