Activiti is an open source, standalone workflow engine. OK, it is more than just a standalone workflow engine. Activiti calls itself a "a light-weight workflow and Business Process Management (BPM) Platform targeted at business people, developers and system admins". Workflow is one of several different domains that can be addressed with a graph-based execution language, but it is the only one this book concerns itself with.
The Activiti engine is responsible for managing deployed processes, instantiating and executing processes, persisting process state and metadata to a relational database and tracking task assignment and task lists.
Activiti is built on the idea that any process can be described as a graph or a set of connected nodes. Workflows are described with "process definitions" using an XML-based language called Business Process Model and Notation (BPMN). BPMN is a standard for modeling business processes. It's one example of a graph-based execution language...
