[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] loosely and tightly coupled systems and type annotation
If you don't want to read yet another rant against *imposing* type annotation in XML please delete... Thinking again and again on what's the difference between loosely and tightly coupled systems and how this apply to XML... In real life there is a clear distinction between loosely and tightly coupled systems: when I press on a power switch to put the light on it's a tightly coupled system but when I do a phone call to order a book it's a loosely coupled system. In a tightly coupled system, I have a direct control over the operation and if I had access to the button controling the printer which will print the book I order, this would be a tightly coupled system too. Tightly coupled systems are usually fast and safe in that the risk of transmission errors is very low. Loosely coupled systems are usually more error prone (the ISBN number of the book I want to order may be misunderstood by the clerk who will enter it) but usually much more flexible and subject to added value: if I don't remember the ISBN number I can still say I want the latest book on W3C XML Schema by a guy with a Dutch name and a publisher which puts animals on all its books and get a chance to be understood. In computer systems, the situation is not so clear: both tightly and loosely coupled do exchange sequences of 0 and 1s and the difference is more subtle. For instance, everyone agrees that XML enables loosely couple systems and that this is a Good Thing, but that doesn't mean that using XML is enough to build a loosely coupled system and using XML to reinvent Corba IMO doesn't make a system loosely coupled. The distinction is thus more subjective than this and lies in the ability to enable and facilitate different interpretations of the documents which are exchanged. Any feature which decreases the number of possible interpretations (such as type annotation) tighten the coupling between systems and if it is legitim and needed for some applications, this shouldn't be imposed to all the applications... Eric -- See you in San Diego. http://conferences.oreillynet.com/os2002/ ------------------------------------------------------------------------ Eric van der Vlist http://xmlfr.org http://dyomedea.com (W3C) XML Schema ISBN:0-596-00252-1 http://oreilly.com/catalog/xmlschema ------------------------------------------------------------------------
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