Wikipedia defines the “Workflow Engine” as:
A software application that controls and executes simulated computer processes.
and from the same source, Business Process Management is defined as:
A holistic management approach to align the organization’s business processes with the needs and needs of customers
Consequently, these nouns should not be used interchangeably; A "workflow mechanism" is a general mechanism used to model any workflow, while a "business process management mechanism" is a concrete implementation of a "workflow mechanism" that models business process management.
So, you can make an analogy, "Workflow Engine" is a block of wood, because the "Business Process Management Mechanism" is a carved wooden cane.
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