IBM BPM, V8.0.1, All platforms > Get started with IBM BPM > Key concepts > BPEL processes and human tasks > Human tasks overview

Scenarios for invoking tasks

Tasks can be invoked in various ways.

Invocation of task components using the Human Task Manager API

Tasks can be instantiated by using the Human Task Manager API. Human Task Manager API clients use the API to create and start task instances, and query and manipulate task instances. For task invocation, the API provides methods to create and start the following kinds of tasks:

• Stand-alone and inline invocation tasks
• Stand-alone to-do tasks
• Collaboration tasks

Administration tasks cannot be invoked using the API because they are invoked in the context of a BPEL process.

The API supports the following interaction styles for tasks:

• Synchronous invocation of the task and the associated service

  This interaction style uses the callTask method. For one-way operations, the invocation returns after triggering the execution of the task and the service component. For request-response operations, the invocation waits until the service and task are complete and the result of the invocation is returned.

  This style of interaction can be applied to invocation tasks only.

• Asynchronous invocation of the task and the associated service

  This interaction style uses the startTask method. For both one-way and request-response operations, the invocation returns after triggering the execution of the task and the service component. In addition, for request-response operations, the invocation returns a result asynchronously that is stored as an output or fault message in the context of the invocation task. The invoking API client must retrieve the result programmatically using the API methods. Alternatively, you can use a reply handler to ensure that the asynchronous response is returned to the client as soon as the response becomes available.

  This style of interaction can be applied to to-do, collaboration, and invocation tasks.

The Human Task Manager API is provided as an Enterprise JavaBeans (EJB) implementation, a web service implementation, a JMS message implementation, and a REST implementation. The API methods are similar for all implementations, but differ in their functional scope.

Invocation of to-do tasks as SCA service components

A stand-alone to-do task represents a SCA service component that can be invoked by an SCA client asynchronously. The mechanisms provided by SCA are available for connecting SCA clients and stand-alone to-do tasks. This includes the SCA means to define the following:

• Wires that connect an SCA client reference and the interface of a component representing a to-do task
• SCA qualifier settings for component references and interfaces that control aspects, such as interaction style, transaction behavior, and interaction reliability

In addition, a stand-alone to-do task can be invoked by an SCA client that is implemented as a BPEL process. In this case, the connection must be considered on both the SCA and process levels. Viewed on the SCA level, the SCA client reference is connecting to the interface of an SCA service. Viewed on the process level, the partner link of an invoke activity is connected to a to-do task.

Invocation of inline to-do tasks

A to-do task can be specified in the context of a human task activity in a long-running BPEL process. In this case, the task does not have a representation on the SCA level, instead it is part of the SCA component representing the BPEL process. The task acts as a service provider to the human task activity. Whenever the activity is reached during process navigation, the to-do task is invoked asynchronously.

Invocation of an SCA service with an invocation task

A stand-alone invocation task serves as an access component to an associated SCA service. The association with the service is defined on the SCA level: the task represents an SCA client that is wired to an SCA service component. The invocation of an invocation task involves both Human Task Manager and SCA levels. The invocation task itself is invoked by the Human Task Manager API, either synchronously or asynchronously. The task (SCA client) then invokes the associated SCA service component in the same way as the task was invoked.

The modeling of the association between the task and the service is done on the SCA level. The concepts and mechanisms provided by SCA are therefore available for connecting stand-alone invocation tasks and SCA service components. This includes the SCA means to define the following:

• Wires that connect an SCA client reference and the interface of a service component
• SCA qualifier settings for component references and interfaces that control aspects, such as interaction style, transaction behavior, and interaction reliability

In addition, a stand-alone invocation task can be connected to an SCA component that is implemented by a BPEL process.

Invoking a BPEL process through an inline invocation task

An inline invocation task can be specified in the context of a receive or pick activity, or an event handler in a BPEL process. The task does not get a representation on the SCA level, instead it is part of the SCA component that represents the BPEL process. Nonetheless, the task acts as a client to the BPEL process. Whenever the task is invoked by the Human Task Manager API, the task in turn invokes the BPEL process in the same way as it was invoked.

See

1. Factors affecting the behavior of stand-alone invocation tasks and their service components
   
2. Scenario: stand-alone invocation tasks that support the asynchronous invocations of services
   
3. Scenario: stand-alone invocation tasks that support asynchronous and synchronous invocations of services
   

Human tasks overview

Related concepts:
Service qualifiers
Factors affecting the behavior of stand-alone invocation tasks and their service components
Scenario: stand-alone invocation tasks that support the asynchronous invocations of services
Scenario: stand-alone invocation tasks that support asynchronous and synchronous invocations of services

Related information:
Create API event handlers