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Few basic concepts of business process management are briefly described below.

Business Process

A business process is typically a collection of related and structured activities or tasks, that depicts a business use case and produces a specific service or output. A process may have zero or more well-defined inputs and an output. During the execution of the business process, it executes its sub-processes synchronously or asynchronously for producing the final output. During the execution, it may interact with both humans or equipment.

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Final Output: Sends acknowledgement. This is the final output which is sent back to the client who initiated the business process.

Process Instance

An instance of a process is a specific example of a process workflow. For example, if a particular process defines a banking customer requesting a bank load, then an example instance of this process is Mr. Smith requesting for 50,000 USD and getting approval for it. Every time a banking customer makes a request for a loan, that request triggers a new process instance in the BPM system, which flows through the elements of the process workflow according to its design.

Business Process Execution Language (BPEL)

BPEL is the industry standard for business process orchestration. It is an XML-based language used for the definition and execution of business, as well as scientific workflows using Web services. In other words, BPEL is used to write business processes by composing Web services together with orchestration. The outcome is a composite Web service.

Although these business processes may interact with humans, the WS-BPEL standard does not specify human interactions. As a result, a business process defined by WS-BPEL alone can not have human interactions but only with Web services. The WSO2 BPS facilitates defining and using human tasks into business processes.

Orchestration Vs. Choreography

Web services can be composed using two approaches: orchestration and choreography. In orchestration, there is a central director to coordinate the services. In contrast, choreography contains no central director and each contributing service should have an understanding of participant services.

For composing Web services for a business process, orchestration is a better option for reasons such as simpler process management, loose-coupling between participating Web services, ease in error handling, standardization etc.

Abstract and Executable Processes

Based on the definition of the actual behavior required by a business process, it can be design in two ways using WS-BPEL: abstract and executable. Abstract processes are intended to hide some operational details of the process. As a result, they do not include executable details like process flows. Executable business processes are used to model the actual implementation of the business process.

An abstract process is denoted under the "http://docs.oasis-open.org/wsbpel/2.0/process/abstract" namespace and an executable process is denoted under the "http://docs.oasis-open.org/wsbpel/2.0/process/executable". Additionally, there are syntactical differences between an abstract and an executable BPEL process.

Asynchronous and Synchronous Communication

BPEL processes can also be categorized based on how it invokes an operation of a partner service: synchronous and asynchronous. It is not possible to use both methods when invoking a partner service's operation, as it is dependent on the type of the partner service operation also.

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Usually asynchronous services are used for long-lasting operations and synchronous services for operations that return a result in a relatively short time. Typically, when asynchronous Web services are used, the BPEL process is asynchronous.