Hi Kevin, On Fri, 22 Feb 2002 15:27:10 -0600, [EMAIL PROTECTED] wrote:
> Ovidiu and Stefano, > > First, I'm new to cocoon, but not the methodology. Welcome! One more head to think about problems and come up with a way to solve them ;-) > I'm in the process of prototyping a conversion from a home grown (Flow > based) framework to Cocoon 2. I was hoping to discover that it was > included. I had put a small amount of effort in defining an XML syntax, > because the existing syntax is compiled into java objects...but I decided > it would be in the best interest of the company to jump into a well > supported project such as Cocoon. > > Here are my thoughts and requirements for our system: > - web service or xml-rpc based interaction > - multiple web service invokations based on dynamic request parameters (per > request) > - web service request message creation (inline transformation) based on > request xml (I think I can already create xml inline for delivery as a > request to a web service) > - content aggregation and inline transformation (already in C2) for either > web service request delivery or response This sounds very similar with the work being done by the HP group I work in to use Cocoon as a SOAP server. I'm sure we can find a way to expose the same business logic as a Web application or a Web Service, and have Cocoon drive them both. > I have defined Flow and FlowOperation as the primary concepts in the > system. A Flow has one to many flow operations. A flow operation can do > anything you can do with java, as long as you create a Controller to handle > it. The flow is invoked as something like: > http://mycompany.com/RootController.jsp?flow=ViewPerson&id=128282722. > Forms post to flows, and all links reference flows. You can then add, > remove, or modify flowOperations without the tight coupling of the UI. If I understand this right, the model you describe (model-view-controller) is very similar with the model I described in the previous email. The controller is the flow layer, and it drives the pages to be presented to the client browser or the original requester, in case of a Web service. > With that said, since I'm very new to C2, I'll stick to just giving > feedback on how I want to use C2. I'm unclear on what is exactly already > present in the project, but I see a great deal of potential. > > I would be extremely interested in contributing to the development of a > Flow control layer with C2....because we are looking to convert our system > right now. I'm ready to start today, but I'll definitely need a guiding > light to get started. > > I will say that I'm interested only in an xml-based flow syntax, possibly a > much simpler version of one I was considering for the home grown version. > > Please let me know if I can help, or if you can point me in a direction > where Cocoon 2 already fulfills my needs. There was quite a bit of discussion on the topic of flow control, checkout the threads on Cocoon-dev: http://marc.theaimsgroup.com/?l=xml-cocoon-dev&w=2&r=1&s=flowmaps%3A+the+wrong+approach&q=t http://marc.theaimsgroup.com/?w=2&r=1&s=%5Brt%5D+Managing+Flow+and+Resources&q=t http://marc.theaimsgroup.com/?l=xml-cocoon-dev&m=100802231017059&w=2 I am currently investigation the use of so-called "continuations" to help in describing the flow as a program in a programming language, rather than as a finite state machine in XML. I believe this approach is much more powerful and easier to write applications in, than with the finite state machine approach. Check out these two papers to understand the difference: http://youpou.lip6.fr/queinnec/Papers/webcont.ps.gz http://www.cs.rice.edu/CS/PLT/Publications/esop2001-gkvf.ps.gz > ================== Flow Config ========================== > > <?xml version="1.0" encoding="UTF-8"?> > <site> > <flowOperationRegistry> > <flowOperation default="true" classname=" > com.iverticalleap.presentation.flow.FlowOperation"/> > <flowOperation name="loadSubjectListXML"> > <delegate>/jsp/FilterFormController.jsp</delegate> > </flowOperation> > <flowOperation name="xsltDisplayTransformation" classname=" > com.iverticalleap.presentation.flow.XsltTransformationDisplayFlowOperation > "> > <delegate>/jsp/TransformationController.jsp</delegate> > </flowOperation> > <flowOperation name="xsltContentTransformation" classname=" > com.iverticalleap.presentation.flow.XsltTransformationContentFlowOperation > "> > <delegate>/jsp/TransformationController.jsp</delegate> > </flowOperation> > <flowOperation name="reflectionContentFlowOperation" classname=" > com.iverticalleap.presentation.flow.ReflectionContentFlowOperation"> > <delegate>/jsp/ReflectionController.jsp</delegate> > </flowOperation> > </flowOperationRegistry> > <flowList> > <!-- the following are the ideas i've come up with --> > <!-- 1 (basic) --> > <flow name="DisplayCreateStudentFlow"> > <flowOperation refname="loadSubjectListXML"/> > <flowOperation refname="loadClassListXML"/> > <flowOperation refname="xsltDisplayTransformation"> > <propertyList> > <property name="xsltUrl">/jsp/admin/createPerson.xslt</property> > </propertyList> > </flowOperation> > </flow> > > <!-- 2 (same thing but with reflection so you don't have to create the > controller --> > <flow name="DisplayCreateStudentFlow"> > <reflectionFlowOperation name="loadSubjectListXML"> > <invoke methodName="getSomeObject" className=" > com.iverticalleap.service.SomeService"> > <parameter name="identity"> > <value><!-- value is dynamically derived from posted variables > --> > <invoke methodName="getParameter" className=" > java.servlet.http.HttpServletRequest"> <!-- also thought about calling this > an <implicitObjectInvokation name="request"> --> > <parameter name="parameterName"> > <value>PersonIdentity</value> <!-- html form variable > name --> > </parameter> > </invoke> > </value> > </parameter> > </invoke> > </reflectionFlowOperation> > <flowOperation refname="loadClassListXML"/> > <flowOperation refname="xsltDisplayTransformation"> > <propertyList> > <property name="xsltUrl">/jsp/admin/createPerson.xslt</property> > </propertyList> > </flowOperation> > </flow> > </flowList> > </site> If I understand the above description right, the flow is described as a finite state machine, where flow names are states (DisplayCreateStudentFlow for example), and the transition events are method names. For a given user, the application is in one possible state in any moment in time, and it transitions to a different state based on an event. I think the finite state machine approach is difficult to extend to complex sites. It is very difficult, and rather limiting, at least for me as a programmer, to think the application as a finite state machine only. Any time I need to introduce a new state in my application, I have to reconsider all the transitions to that state, and the impact it has on the existing system. I'd be more happy if I can describe the flow in a "normal" programming language, where I can express complex flow by writing a program. This is what I'm trying to do in the Schecoon sub-project. Using the Scheme language, and the fact that continuations are first class objects in it, I want to implement the ideas described in the resources I mentioned earlier. But the language to describe the flow will not be Scheme, but one with a more familiar syntax. Best regards, -- Ovidiu Predescu <[EMAIL PROTECTED]> http://www.geocities.com/SiliconValley/Monitor/7464/ (GNU, Emacs, other stuff) --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
