Using '.' means 'current directory', and '..' means 'parent directory'. For a build.xml file, the directory in which the build.xml file resides is considered the current directory.
It is usually a standard practice that basedir is set to '.', and not to '..'. Also it is another standard practice that build.properties appears in the same directory as build.xml. And usually the build.xml file appears in the base directory of the project (in your case, move build.xml to where build.properties is located)
If you really do not want to move your build.xml or build.properties file, or change the basedir, use this: