Cloud Foundry: Design and Architecture
Derek Collison discusses the goals, the design premises and patterns employed in creating the architecture of Cloud Foundry, VMware’s open source PaaS, unveiling internal architectural details.
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Posted by Josh Long on May 22, 2010
Alfresco Software, makers of the leading open source enterprise content managment (ECM) system announced Monday their open source Activiti Business Process Managment (BPM) project, led by jBPM creator, former JBoss jBPM lead and BPM authority Tom Baeyens. Joram Barrez, also a former jBPM team member, joins him as a core Activiti developer. Alfresco has long embedded jBPM in their product offering, and will continue to support it going forward. Ultimately, Alfresco will also include Activiti in future releases.
Activiti is a new, Apache 2 Licensed open source project that offers a light weight, embeddable BPM engine with BPMN 2.0 support. In the BPM market, there are many specifications that - arguably - never quite offered leadership on all the main problems solved by a BPM engine, or workflow engine. BPEL is often criticized for providing too limited a runtime model to build more complex processes. More confusingly, BPMN 1.0 emerged and specified a very rich set of symbols to describe processes, but did not specify execution semantics, as BPEL did. Many vendors clamored to build BPMN tools that round-tripped to BPEL, but this was untenable as BPEL could not describe many things that could be drawn in BPMN.
Many engines were content to offer alternatives, including jBPM. jBPM provides a simpler, proprietary XML syntax called jPDL that could be hand written, and easily embedded in applications.
Activiti takes a different tact, choosing instead to embrace BPMN 2.0, which specifies both execution semantics, as well as the visual description of a process. This enables a standard, straightforward, round-trip friendly environment for business analysts as well as engineers dealing with the runtime representation of a process. Like jBPM (and, indeed, any well engineered project) Activiti decouples the process model from the language, and so it is conceivably possible to write other process languages on top of the model. Unlike jBPM, Activiti has no proprietary format, requiring confusing translation to realize BPMN 2.0: BPMN 2.0 is the native format.
Activiti ships with a visual modeler (called Acitviti Modeler) that can be used to model very sophisticated diagrams. BPMN 2.0 is also fairly compact, and convenient. Some places are a bit more verbose than jPDL, however, and so support for "shortcuts" in the schema has been introduced. These "shortcuts" are ultimately translatable to valid BPMN 2.0, and so don't represent proprietary extensions.
Activiti is lightweight, and easily integrated with existing applications, which naturally dovetails with the goals of the Spring framework. Besides supporting BPMN 2.0 in of itself, one might speculate at other possible uses for a workflow engine: Spring Web Flow describes workflows in terms of a web page navigationl Spring Batch describes workflows for processing batch pipelines, Spring Integration "infers" process state from events, etc. SpringSource has positioned Dave Syer, lead of the Spring Batch project, to represent the Spring community in the Activiti team, with the intention of bringing BPMN to Spring users.
Developers who would like to get started should take a look at the 10 Minute Tutorial, and when they want to learn more, should consult the Activiti User Guide. The project is being run autonomously - a part of Alfresco, but geared up to build its own community.
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