Apache Ivy: XML Namespace and Imported Properties

I was looking at an Ant build.xml file this morning and noticed an XML namspace delcaration in the root <project> element:

<project name="${project.name}" xmlns:ivy="antlib:org.apache.ivy.ant">

I figure this XML namespace is so that all of the Ivy tasks sprinkled throughout the buildscript know which resource to look inside for task definitions (<ivy:configure>, <ivy:resolve>, etc.), but was hoping for a more thorough explanation of the syntax of this statement.

What is the concept of a "namespace" in Ant world? Is this xmlns:ivy= attribute pointing towards a JAR?
Where would this org.apache.ivy.ant JAR/resources/whatever live?
What is antlib and where is it defined?

Also, just a fleeting thought here, do Ivy files (ivy.xml) have the ability to import properties files and use their property values? I looked in the Ivy documentation but couldn't find references to any import-type statements.

Thanks in advance!

Solution

The namespace is just like any other namespace as far as XML is concerned. But, Ant is using antlib: as a URL scheme to know that it should look for an org/apache.ivy/antlib.xml file in the classpath. See the antlib Type in the Ant manual.

Since it's looking for a classpath, the antlib.xml can be anywhere a classloader can find it. The default setup is to put the necessary jar file in the <ant install>/lib directory. You can also start ant with -lib to specify a different directory or just set the CLASSPATH (not recommended).

Yes, you can can import properties files. See the Ivy manual info on multi-projects. Ivy supports the ${property} syntax and you can use Ant's <property> task to load a file that Ivy can use. You can also use <property> elements in ivysettings.xml if you want to define 'global' values for Ivy.