XML really that crucial for Web Services?

Question

No doubt Web Services are here to stay. I've tried to learn about them by reading different sites on the internet. But so far, I've only been able to read positive praises of XML. Such as the buck-a-car system. However, I'm interested in some of the negatives of XML. I want to know where XML will NOT work and is discouraged. Only be considering the negatives and limitations can I understand whether XML is appropriate for my system. (e.g., is XML good for database-to-database communications?)
When I look at the average XML file, there is so much overhead such as the DTD and descriptive XML tags. If one XML file was used to store a lot of information, it would be acceptable. But if I were to say, write a chat program, it doesn't seem wise to send an XML file for each sentence/letter typed.
And if I wanted to synchronize two databases through the internet, wouldn't it be faster to just send each record as a stream of bytes and have the other database parse that? Instead of converting the record to XML and back.
Or if I was communicating between the server and an applet, should I convert all requests into XML even though I am well aware of the format of the applet?
I personally see XML being used in only a small number of applications such as an initial handshaking process before communications.
I know it must be because I have a lack of understanding. If anyone has comments or even agrees, your feedback is more than welcome.

Answer 1

Well of course XML is crucial for Web Services, because the messages they pass back and forth are in XML format. (Of course that's only for the current buzzword "Web Services", some of us have been producing Web Services where the messages are in e-mail format for years now.) You're right, using XML for everything is stupid. And if you control both ends of the conversation, you can talk in any language you like, and you probably should. But if you want to talk to large numbers of people, and you don't want to limit what kind of data you might send, then you need a standard framework to do that, and XML is it. That doesn't mean that XML will replace SMTP or any other existing standard format, just that it's likely to be widely used in the future for sending generalized data between systems.