Package org.apache.commons.workflow

This package contains the core interfaces and classes that define the major components of the workflow management system.

See:
Description

Interface Summary

Activity	An Activity represents an ordered sequence of Steps that comprise the executable actions necessary to accomplish a business task.
Block	A Block is a Step that can include nested Steps.
Context	A Context represents the dynamic computational state of a workflow process that is currently being executed.
ContextListener	A ContextListener registers its interest in receiving ContextEvent notifications when the occur on a particular Context of interest.
Descriptor	A Descriptor is a description of the mechanism by which an arbitrary Java object (typically a JavaBean) is referenced.
Descriptors	Implementing Descriptors indicates that the corresponding object has an associated list of Descriptor objects associated with it, which can be manipulated through the methods defined in this interface.
Iterator	An Iterator is a Block that conditionally repeats the nested Steps associated with the Block more than once (such as a Block that implements "while" or "for" functionality).
Owner	Owner represents the common characteristics of Activities and Blocks (that is, Steps that allow nested Steps, such as those that implementat conditionals and iteration).
Registry	A Registry is a Singleton that provides registration and lookup facilities for Activity instances.
Scope	A Scope is a collection of arbitrary Java objects, keyed by String-valued names.
ScopeListener	A ScopeListener registers its interest in receiving ScopeEvent notifications when the occur on a particular Scope of interest.
Step	A Step represents a single executable action that can occur during the completion of an Activity.

Class Summary

BlockState	BlockState represents the current dynamic execution state of a Block that is executing nested Steps.
ContextEvent	A ContextEvent provides notification to a ContextListener that a specified event has occurred for the specified context.
ScopeEvent	A ScopeEvent provides notification to a ScopeListener that a specified event has occurred for the specified scope.

Exception Summary

StepException	A StepException is used to report problems encountered during the dynamic execution of a specific Step.
WorkflowException	A WorkflowException is the base class for exceptions related to the workflow engine framework.

Package org.apache.commons.workflow Description

This package contains the core interfaces and classes that define the major components of the workflow management system. There are divided into several categories, as follows.

The static representation of a set of possible workflows is represented internally as a tree of objects that implement the following interfaces. There is a one-to-many relationship between each component and the one immediately below it.

• Process - A "business process" that is composed of several independent activities, possibly executed by different individuals at different times. NOTE - not yet implemented.
• Activity - A particular "business task" that may be comprised of one or more discrete computations, typically involving interaction with a single individual in a manner that is outside the scope of the workflow system.
• Step - A discrete computation that can be performed as part of an Activity. Informally, the set of defined Steps can be considered to be the "instruction set" of a "workflow computer". Several sets of predefined Step implementations are included, and additional sets can be defined by workflow implementations layered on top of the basic classes (for example, the web-layer Steps are valid only within a web application, but such a workflow implementation can still use all of the core Steps).

The components described above are typically represented textually in an XML document whose format is not of interest to the core platform. However, the internal representation of these components is shared among concurrent users of those components, so the corresponding object tree (and the bean properties used to represent the linkages) should be considered read only after it is constructed.

The dynamic state of a computation is represented by the following components. Each "in progress" computation, whether executed by the same thread or different threads, must have its own Context to represent the current state.

• Context - The current execution state of a particular Activity. Each Context provides an evaluation stack for in-process computations, plus access to one or more Scopes for interacting with the object model of the surrounding application environment.
• Scope - An implementation of java.util.Map that provides a pluggable mechanism to attach the workflow engine to the object model of a surrounding application. Every Context provides at least one Scope (called "local"), and additional Scopes can be registered by the application. For example, a web application implementation of the workflow system would typically register Scope implementations that map to the attributes of servlet requests, HTTP sessions, and the servlet context. Implementations in other environments can provide Scope adapters to their own object storage mechanisms, without affecting how Step implementations interact with beans stored in those Scopes.