java - How do XML namespaces work without a working network connection?

Question

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context"

       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.1.xsd">

  <context:component-scan
      base-package="com.springinaction.chapter01.knight" />

</beans>

The above example shows an example of an XML file with several namespaces. What is the purpose of these namespaces and most importantly why do they work even where there is no Internet connection?

I think the second bit that starts with xsi:schemaLocation contains the XML schema files which are used to validate the structure of the XML document. How come these still work if I run the application that uses this configuration file on a machine that is not on a network? Are the URLs somehow aliases to JAR files?

Answer 1

Try to ignore the fact that many namespace names look like URLs that you might type into your browser. They are just random strings of characters, they aren't addresses of resources on the web. The reason people adopt this convention is that it shows who "owns" the name - it's clearer what http://www.w3.org/2001/XMLSchema refers to than if they had chosen "xsd1.0" as the namespace name, and it's less likely to conflict accidentally with a name chosen by someone else. Some people also like the fact that you can put documentation at the relevant location, but no XML software will go looking for the documentation automatically.