Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Re: Where does the "nothing left but toolkits" myth come f
 On Sun, 6 Feb 2005 19:56:22 -0600, Kenneth Stephen <marvin.the.paranoid@g...> wrote: > > > I dont understand how PI's can reduce > portability. It seems to me that PI's are intended to achieve the > opposite effect : if additional knowledge (than is visible to a basic > XML processor) is visible to an XML application specific processor, > then the PI serves as a signal to activate the application level > processor. This doesnt change any the semantics of the data w.r.t. > non-application specific data. There are a couple of potential interop problems that PI's can open. One is that applications can ignore PI's that they don't understand (*processors* have to pass them on to an app, but apps may not round trip them). Or at least this was true in SGML days; apps tended to step on each others' PIs. I don't remember specifically why they were forbidden in SOAP, but I think it was to avoid the possibility of "secret handshakes" between a service requester and provider that aren't described by the schema/WSDL contract. One big use of PIs (again in SGML days, I haven't touched them for some time!) was for an app to communicate with itself or its partners some information that coudn't be put in elements or attributes without violating the schema. That's convenient for everyone, and not a problem if it is just describing some bit application state that is irrelevant in the greater scheme of things, but in Web services that could be mis-used in a way that inhibits interop. For example, if a service implemented a formal service contract but didn't understand a PI that the client used to specify something important, it would not respond the same way as another implementation of the same service contract did. SOAP nipped that scenario in the bud by forbidding PIs altogether. So, properly used a PI does not change the data semantics, but as with everything else, XML Doesn't Care. and PIs give people rope with when they have cheerfully hanged themselves. Of course, they also provide plenty of rope to tie up loose ends, e.g. letting an instance offer hints about what stylesheet to use to display it. 
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! 
Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|
|||||||||
