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A workflow manager is a sequencer. That is the basic pattern. You find it in everything from workflow to musical composition to video editing to animation. The difference is the degree of coupling strength from loop to loop that ensures position. OTW, a real-time editing system, meaning, the human can open any sequence or set of sequences at any time and adjust. Two pieces workflow theories sometimes leave out are pace and transition. A system must be operable and comfortable. len -----Original Message----- From: Costello, Roger L. [mailto:costello@m...] Sent: Tuesday, April 28, 2009 8:43 AM To: 'xml-dev@l...' Subject: Here's what I've learned over the last several months about workflow, document-based designs, and system design Hi Folks, Over the last several months I've pored over these extraordinary articles, technology, and book: [Article] Building Workflow Applications by Michael Kay [Article] Business artifacts: An approach to operational specification by A. Nigam and N.S. Caswell [Technology] XProc (XML Pipeline Language) [Book] Workflow Management by Wil van der Aalst and Kees van Hee Here's what I've learned: 1. For years I've heard "Separate the data from the application" and "Separate the User Interface (UI) from the application." I've now learned of the importance of separating process management from applications. Check out this graphic: http://www.xfront.com/separate-process-management-from-applications.gif Here's what a workflow management system does: The management system ... ensures that no steps [in a process] are skipped, that they are carried out in the correct order, that tasks can be performed in parallel where possible, that the correct applications are called in to support a task, and so on. Separating management from applications has a number of important advantages, including: Applications no longer require any management functionality, and hence are simpler and completely independent of their context or place in the business process. This makes it possible to rearrange the business process at a later stage. (See p. 147-148 of van der Aalst's book for a complete list of advantages) 2. Process is important. It can make or break a system. 3. Recently it dawned on me that NVDL is a micro workflow management system. How so? Here's my (short) explanation: http://lists.dsdl.org/dsdl-comment/2009-04/0005.html 4. XProc is very cool: you create a .xpl file which defines a process (pipeline), hand it off to an XProc processor (such as Norm Walsh's Calabash) and the processor takes care of managing the pipeline. XProc can be used to manage interactions with Web services. Here's an example of an XProc pipeline interacting with multiple RSS feeds: http://lists.w3.org/Archives/Public/xproc-dev/2009Apr/0104.html 5. A workflow management system invokes a task, providing it with the appropriate information and resources. The task may be activated either by: - invoking an API, or - sending it a document "By API" means that you focus on creating a standard interface, i.e. specify a subroutine's name, parameters, and return value. Thus, you create an Interface Control Document (ICD). "By document" means that you focus on creating a standard XML vocabulary. Thus, you create a Data Specification. 6. There are benefits to having a workflow management system manage the flow of documents rather than managing API calls. The benefits particularly accrue when the documents are based on key business documents, i.e. the documents used in the actual running of a business. One benefit is that you have an operationally centered view of the business: the process definition mirrors the business process and the documents mirror the key business documents. This produces a model that is a rich representation for analyzing and managing the business. (See the Nigam/Caswell and Kay articles for further elaboration on the benefits) Based on what I've learned, here's my brief sketch of how to create systems: Step 1: Identify the process Step 2: Identify the key business documents needed by the process Step 3: Identify the data used by the workflow management system to route the business documents through the process (van der Aalst calls this "case attributes") Step 4: Create a data specification for the business documents, i.e. write prose that describes the data at an operational level Step 5: Derive implementations from the data specification, i.e. create an XML Schema, Schematron schema, and so forth Step 6: Create a process definition, e.g. create an XProc file and/or a BPEL file Step 7: Create your User Interfaces and databases Step 8: Deploy your workflow management system That's a snapshot of what I've learned. I hope that you've found it useful. I welcome your additional insights. /Roger [1] Michael Kay: http://www.stylusstudio.com/whitepapers/xml_workflow.pdf [2] Business Artifacts: http://findarticles.com/p/articles/mi_m0ISJ/is_3_42/ai_108049865/ [3] XProc Tutorial: http://www.xfront.com/xproc/ [4] Workflow Management: http://www.amazon.com/Workflow-Management-Methods-Cooperative-Information/dp /0262720469/ref=sr_1_1?ie=UTF8&s=books&qid=1239573871&sr=8-1 [5] NVDL tutorial: http://www.xfront.com/nvdl/ _______________________________________________________________________ XML-DEV is a publicly archived, unmoderated list hosted by OASIS to support XML implementation and development. To minimize spam in the archives, you must subscribe before posting. [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ Or unsubscribe: xml-dev-unsubscribe@l... subscribe: xml-dev-subscribe@l... List archive: http://lists.xml.org/archives/xml-dev/ List Guidelines: http://www.oasis-open.org/maillists/guidelines.php
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