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An agent is a named point of communication within a system. Communication within and between systems is accomplished by sending a message from one agent to another. A single system can have several different agents representing different communication alternatives. For example, a system may have different agents to support inbound and outbound communication, communication by different protocols, different propagation frequencies, or other alternatives.

You should define each agent that you will use to communicate events in the Event Manager. Each agent's name must be unique within its system. The agent can be referenced in code within Oracle Workflow by a compound name in the following format:

<agent_name>@<system_name>

For example, the agent WF_IN within the system HUB could be referenced as WF_IN@HUB.

After defining the agents on your local system, you should set them up for event message propagation by scheduling listeners for local inbound agents and propagation for local outbound agents. See: Scheduling Listeners for Local Inbound Agents, Oracle Workflow Administrator's Guide and Scheduling Propagation for Local Outbound Agents, Oracle Workflow Administrator's Guide.

Assigning a Direction to an Agent

When you define an agent in the Event Manager, you must specify the direction of communication that the agent supports on its local system.

Assigning a Protocol to an Agent

You must associate each agent with the protocol by which it communicates messages. The protocol specifies how the messages are encoded and transmitted. For a message to be successfully communicated, the sending and receiving agents must use the same protocol.

A protocol can represent a network standard, such as SQLNET. It can also represent a business-to-business standard that defines the higher-level message format and handshaking agreements between systems in addition to the network standard.

The Business Event System interacts with an agent through an AQ queue. You can use AQ to perform the propagation of messages by the SQLNET protocol which it supports. In Oracle9i Database and higher, AQ also includes Internet access functionality that lets you perform AQ operations over the Internet by using AQ's Internet Data Access Presentation (IDAP) for messages and transmitting the messages over the Internet using transport protocols such as HTTP or HTTPS. Additionally, the Messaging Gateway feature of AQ in Oracle9i Database and higher enables communication between applications based on non-Oracle messaging systems and AQ, letting you integrate with third party messaging solutions. You can also implement other services to propagate messages by different protocols. The following table shows which services you can use for various protocols, depending on your database version.

To implement a custom protocol, you must perform the following steps:

If an agent supports inbound communication, you must specify the address by which systems can communicate with it. The format of the address depends on the agent's protocol. For agents that use the SQLNET protocol, the address must be in the following format to enable AQ propagation:

<schema>.<queue>@<database link>

In this format, <schema> represents the schema that owns the queue, <queue> represents the queue name, and <database link> represents the name of the database link to the instance where the queue is located.

Note: You must enter the database link name exactly as the name was specified when the database link was created. For example, if a database link is named ORA816.US.ORACLE.COM, you must enter that complete name in the address of an agent on that database. You cannot abbreviate the name to ORA816.

The names of the database links that you want to use for the Business Event System should be fully qualified with the domain names. To confirm the names of your database links, use the following syntax:

                 SELECT db_link FROM all_db_links

See: Creating Database Links, Oracle Workflow Administrator's Guide.

Assigning a Queue to an Agent

You must associate each agent on a Workflow-enabled system with an AQ queue. The local system uses this queue to interact with the agent. To send messages, the system enqueues the messages on the queue and sets the recipient addresses. To receive messages, the system runs a queue listener on the queue. See:

Setting Up Queues, Oracle Workflow Administrator's Guide.

Event messages within the Oracle Workflow Business Event System are encoded in a standard format defined by the datatype WF_EVENT_T. You must assign each agent a PL/SQL package called a queue handler that translates between this standard Workflow format and the format required by the agent's queue. See: Event Message Structure, Oracle Workflow API Reference.

Note: Even if the agent's queue uses WF_EVENT_T as its payload type, a queue handler is still required in order to set native AQ message properties.

Oracle Workflow provides two standard queue handlers, called WF_EVENT_QH and WF_ERROR_QH, for queues that use SQLNET propagation and use the WF_EVENT_T datatype as their payload type. You can use WF_EVENT_QH with queues that handle normal Business Event System processing, while WF_ERROR_QH should be used exclusively with error queues.

Oracle Workflow also provides a standard queue handler called WF_EVENT_OJMSTEXT_QH for queues that use the SYS.AQ$_JMS_TEXT_MESSAGE datatype as their payload type. This queue handler enables communication of JMS Text messages through the Business Event System. See: Mapping Between WF_EVENT_T and SYS.AQ$_JMS_TEXT_MESSAGEE, Oracle Workflow API Reference.

Additionally, Oracle Workflow provides a queue handler called WF_EVENT_OMB_QH, which you can use if you implement Oracle Message Broker with Oracle8i Database to propagate messages between systems by another protocol such as HTTP. See: Setting Up the WF_EVENT_OMB_QH Queue Handler, Oracle Workflow Administrator's Guide and Mapping Between WF_EVENT_T and OMBAQ_TEXT_MSG, Oracle Workflow API Reference.

If you want to use queues that require a different format, create a custom queue handler for that format. Your custom queue handler must include a set of standard APIs to enqueue and dequeue messages in the custom format. See: Standard APIs for a Queue Handler.

Standard Agents

When you install Oracle Workflow, several standard agents are automatically defined for the Business Event System.

These agents use standard queues that are automatically defined when you install Oracle Workflow. See: Setting Up Queues, Oracle Workflow Administrator's Guide.

You can enable or disable the WF_IN, WF_JMS_IN, WF_OUT, and WF_JMS_OUT agents, but you must not make any other changes to their definitions. You must not make any changes to the definitions of the other agents.

Oracle Workflow automatically runs agent listener service components for the standard WF_DEFERRED, WF_ERROR, and WF_NOTIFICATION_IN agents in order to perform deferred subscription processing, error handling for the Business Event System, and inbound e-mail processing for notification mailers, respectively. If you want to use the WF_IN, WF_JMS_IN, WF_OUT, and WF_JMS_OUT agents for event message propagation, schedule listeners for WF_IN and WF_JMS_IN and propagation for WF_OUT and WF_JMS_OUT as well. You do not need to schedule propagation for the WF_CONTROL and WF_NOTIFICATION_OUT agents, however, because the middle tier processes that use WF_CONTROL dequeue messages directly from its queue, and notification mailers send messages placed on the WF_NOTIFICATION_OUT queue. See: Scheduling Listeners for Local Inbound Agents, Oracle Workflow Administrator's Guide and Scheduling Propagation for Local Outbound Agents, Oracle Workflow Administrator's Guide.

Note: Oracle Workflow also includes three additional agents named WF_REPLAY_IN, WF_REPLAY_OUT, and WF_SMTP_O_1_QUEUE, which are not currently used.

The following table lists the default properties for the standard WF_CONTROL agent. See: Cleaning Up the Workflow Control Queue, Oracle Workflow Administrator's Guide.

The following table lists the default properties for the standard WF_DEFERRED agent.

The following table lists the default properties for the standard WF_ERROR agent.

The following table lists the default properties for the standard WF_IN agent.

The following table lists the default properties for the standard WF_JMS_IN agent.

The following table lists the default properties for the standard WF_JMS_OUT agent.

The following table lists the default properties for the standard WF_NOTIFICATION_IN agent. See: Implementing Notification Mailers, Oracle Workflow Administrator's Guide.

The following table lists the default properties for the standard WF_NOTIFICATION_OUT agent. See: Implementing Notification Mailers, Oracle Workflow Administrator's Guide.

The following table lists the default properties for the standard WF_OUT agent.

See Also

To Find Agents

To Update or Delete an Agent

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