What's the difference between XSLT and XSL-FO?

Question

What's the difference between XSLT and XSL-FO ?

Every resource I've read deal with them as if they were 1, or at least very closely tied..

Answer 1

I was wondering about the basis of the question because I thought it was easy to answer, however as soon as you go here: http://www.w3.org/TR/xsl/ it becomes clear that its actually a good question - because pretty much the first thing on the page is this statement:

This specification defines the features and syntax for the Extensible Stylesheet Language (XSL), a language for expressing stylesheets. It consists of two parts:

1. a language for transforming XML documents (XSLT), and
2. an XML vocabulary for specifying formatting semantics.

However, back in the real world, XSLT (which is also what most people will assume you mean by XSL) is a means for transforming XML documents into something else - that something else more often than not being another well structured document probably also formatted as XML (though I've used XSLT to render XML to csv and plain(ish) text).

XSL-FO on the other hand is about formatting - about laying out content on a page or a sequence of pages in a fairly strict fashion. Its useful because it allows you to manage content that is spread across multiple pages, its relatively straightforward to specify the format of a page (or even and odd pages) including headers, footers, borders, columns, etc and have your content flow into that. One would therefore take a load of data in, say, an XML format and then use XSLT to convert that data into a document consisting of XSL-FO that in turn is rendered using an appropriate tool in say PDF for print or other means of distribution.

The use case I have is to take a pile of tabular data, export that data as XML, render that into XSL-FO and from there to PDF which goes to a printer who turns said PDF into a 500 page directory. One specifies in the XSL-FO that one wants page numbers, page breaks in specific circumstances, that there is a table of contents and an index (each based on particular elements) and the rendering process (to PDF) handles filling in the page numbers across the board.

Hopefully you're a bit less confused now..

Answer 2

Aside from the similarities in the acronyms the two technologies used to be part of the same W3C spec(in draft form). It was later decided to split XSL(XSL-fo) and XSLT out into two separate specifications.

Quote from W3Schools:

XSL-FO is Formally Named XSL

Why this confusion? Is XSL-FO and XSL the same thing?

Yes it is, but we will give you an explanation:

Styling is both about transforming and formatting information. When the World Wide Web Consortium (W3C) made their first XSL Working Draft, it contained the language syntax for both transforming and formatting XML documents.

Later, the Working Group at W3C split the original draft into separate Recommendations:

* XSLT, a language for transforming XML documents * XSL or XSL-FO, a language for formatting XML documents * XPath, a language for navigating in XML documents 

A detailed annotation of the chronology can be found on Dave Pawson's Home page: http://www.dpawson.co.uk/xsl/sect1/history.html