The internet works because
- there is a stack of protocols built to make things work. Each protocol solves one thing.
- all miraculously work together because these standards are open.
Tim takes the example of the network stack: Ethernet Packet, Internet Packet, TCP Packet, the port, and the email protocols.
Protocols and standards are everywhere. He takes more examples. When you publish a web page for example: it can be both human and machine-readable. It can be accessed through a URI and when someone follows a link to your web page, their browser opens a TCP/IP connection to TCP port 80 on the machine which is registered as serving the (www.whatever.com, etc) in question. All of that is because the URI specification says that what you can tell about a URI depends on the first bit, in this case HTTP. Tim explains in depth why these relationships exist.
An XML document is a less specified version of an HTML document. The namespace declaration gives a URI indicating the namespace used to interpret this XML though. And more...
An RDF document is based on XML and a triple: a value of some property of some object, or some relationship between some object and some other object. How to figure out what a triple means? A URI defines it, and its standard can be read while dereferencing it. The color example is great! So the stack for this document piles up from the Ethernet to the RDF MS 1.0 and RDF MS 1.0 definition of rdf:type.
A pattern is that each technology evolves into three stages: using numbers or strings, then using a URI, and then a dereferenceable URI. As we move on to later protocols, the protocols themselves become more diverse, so URIs were created instead of simple versions with numbers or strings. "The third stage of civilization is the one at which the identifiers can be looked up on the web.".
This stack prevents one from sending a nasty email to someone and then protesting that the message didn't mean anything. So if the stack is so strict, how does one send a nasty email message when one doesn't mean it? Many protocols have ways of breaking the chain, of including information that is not part of the meaning of the message.
For the email: an attachment. "So being able to refer to something without asserting it, whether you call it attachment, packaging, or quoting, is an important feature of a language. The fact that you can do this removes the last excuse for anyone claiming not to have meant whatever they did say in the main message!"