Docbook - Using Entities to define a shared string

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book [
  <!ENTITY product-name "Docbook">
  <!ENTITY product-version "4.5">
]>
<book>
  <chapter>
    <title>Tutorial: Using Entities to define a shared string</title>
    <para>The latest version of <application>&product-name;</application> is &product-version;.</para>
    <para><application>&product-name;</application> is best used to write documentation.</para>
  </chapter>
</book>