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From Reinhard Poetz <>
Subject Re: Spring "web flow" vs Cocoon Flow/Continuations
Date Fri, 13 May 2005 11:57:46 GMT
thomas wrote:

> --On Freitag, 13. Mai 2005 12:07 Uhr +0200 Sylvain Wallez 
> <> wrote:
>> 3 years ago, the cocoon devs were discussing "flow maps", and addition to
>> the sitemap to define page flow using an XML grammar. We always ended up
>> with verbose XML languages having control structures (the infamous "if"),
>> and then some people came with continuations, at first is Scheme (a Lisp
>> dialect - eck!) and then Javascript, and later pure Java.
>> Having a real programming language allow to *very easily* write complex
>> page flows, as you can use all the language's features for control
>> structures, and simply use regular variables to store the interaction
>> state. Amazingly easy and powerful.
>> The main advandage I see to a declarative approach is that it allows to
>> build visual tools (i.e. graphical editors) to design the flow. But the
>> underlying XML files are very likely to be a real mess in realworld
>> complex use cases.
>> Note however that Cocoon's flow engine is pluggable and that we have 3
>> versions of it today:
>> - flowscript, using Javascript to define the flow (business logic should
>> be kept in Java)
>> - javaflow, a pure java implementation
>> - apples, an experimental implementation (used in Daisy IIRC) which may
>> be actually closer to Spring's approach.
> as i understood it the results of a flowscript-operation don't generate 
> sax-events.

a flowscript (or any other alternative) invokes a pipeline

> so you can use flowscript only at the end of a pipeline. 

the sitemap connects a request with a flowscript call. The flowscript invokes a 
pipeline that produces SAX events.

> that true? and is it equally true for all 3 flow-implementations 
> mentioned above?

that what I said is equal for all 3 alterntaives

  in that case i would think that some logic within the
> sitemap (the infamous "if") wouldn't be so bad (for very comlex problems 
> one could still decide to leave the sax-stream and use flows). 

can't follow you here. what's your usecase?

> but i 
> might very well overlook something obvious or essential.

Reinhard Pötz           Independent Consultant, Trainer & (IT)-Coach 

{Software Engineering, Open Source, Web Applications, Apache Cocoon}


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