File: Data.xml
title 1
author 1
title 2
author 1
title 3
author 1
title 4
author 1
author 2
author 3
author 4
File: Transform.xslt
version="2.0" xmlns:book="books.uri" exclude-result-prefixes="book">
Category:
Output:
title 1
Category:
Science
title 2
Category:
Children's Fiction
title 3
Category:
Children's Fiction
title 4
Category:
Computing