Hello, I just want to give my thoughts to unified pipeline and data conversion topic. In my opinion, the pipeline can't do the data conversion, because it has no information about how to do this. Let's take a simple example: We have a pipeline processing XML documents that describe images. The first components process this xml data while the rest of the components do operations on the actual image. Now is the question, who will transform the xml data to image data in the middle of the pipeline?
I believe the pipeline cannot do this, because it simply do not know how to transform, because thats a custom operation. You would need a component that is on the one hand a XML consumer and on the other hand an image producer. Providing some automatic data conversions directly in the pipeline may help developers that need exactly these default cases but I believe it would be harder for people requiring custom data conversions (and that are most of the cases). The actual architecture allows to fit any components into the pipeline, and only the components itself have to know if they can work with their predecessor or the component following them. That allow most flexibility when thinking about any possible conversions. If a pipeline should do this, you would need "plug-ins" for the pipeline that are registered and allow the pipeline to do the conversions. But then, it is the responsibility of the developer to register the right conversion plug-ins and you would have get new problems if a pipeline requires two different converters from the same to the same data type because the pipeline cannot have automatically the information which converter to use in which situation. The only thing cocoon can help here with is to provide as much "standard" converters for use as possible, but it is still the responsibility of the developer to use the right ones. Best Regards, Jakob -----Original Message----- From: Grzegorz Kossakowski [mailto:g...@tuffmail.com] Sent: Samstag, 10. Januar 2009 23:09 To: dev@cocoon.apache.org Subject: Re: [C3] StAX research reveiled! Sylvain Wallez pisze: > Again I doubt of the real value of a common unified pipeline if all the > responsibility of ensuring proper compatibility between components > (including possible data conversion) is delegated to components. This > leaves a lot of complexity to component implementers (except in the > simple straightforward push scenario), and the features of the pipeline > will be limited to linking the components together and caching. I've been having similar concerns thus I'm eagerly waiting for some non-XML examples that would change my mind. > Furthermore, people will have to take great care of choosing components > that fit together, or they will get exceptions at pipeline execution > time. Hmm... reminds me of some criticism about the StAX stream API :-D LOL! :-) > So let's agree that we disagree. I'll see what you guys come up with and > hope I'll change my mind then. I just wanted to say that I share many points with Sylvain even if it's still hard for me to say which option I prefer. This will require some more thinking... -- Best regards, Grzegorz Kossakowski
