Monday, July 2, 2007

The end of PDF

This post echoes my 8 March 2007 post The end of JPEG, this time pointing to the standardization of print (or paper) specifications. I am reacting to last Friday's post on Andy Updegrove's Standards blog about Microsoft's submission of its XML Paper Specification (XPS) to ECMA International.

PDF is a direct descendant of Interpress, a device independent page description language originally designed at PARC and released in 1980. Although I am linking into Wikipedia, the information there is inaccurate: JaM was indeed based on Forth, and PostScript is a direct descendant of JaM, but Interpress is not really a direct descendant of JaM and PDF is not really a direct descendant of PostScript.

What do I mean by that? Although the same people where involved, JaM and PostScript are philosophically very different from Interpress and PDF. The former was a top notch and very elegant engineering effort by John Warnock to create a real world device independent page description language to replace the device dependent Press page description language.

After JaM was successful, PARC's computer language gurus that were behind Cedar did a clean-sheet design of a device independent page description language carried out with the methodology of specifying a computer language. Although is took advantage of the JaM experience it's author's collaboration, Interpress is much cleaner, more powerful, and more efficient. The main driving forces behind this effort were Butler Lampson and Bob Sproull.

In my view, PDF is more the sibling of Interpress than the son of Postscript, and I believe it is mostly the merit of Ed Taft that PDF has remained a pure and clean language to these days.

Those were the Seventies. If PDF would be specified today, it would very likely be as one of the XML languages. In fact, if one considers the evolution of PDF over the releases, one can say that it is somehow converging to XML.

When they were done with Interpress, what problem did PARC's computer language gurus tackle? In those days there where three computer systems in use at PARC — Cedar, Interlisp, and Smalltalk — and each had their own incompatible document preparation system. Therefore, there was a need for a system independent editable document description language, which would do for WYSIWG editors what Interpress did for printers. The outcome was Interscript and the main authors were Bob Ayers, Jim Horning, Butler Lampson, and Jim Mitchell.

Unfortunately, 1983, when Interscript was finished, was a very turbulent year at PARC and Interpress fell between the cracks. It lingered along in the Spinnaker project and at INRIA Sophia Antipolis, eventually strongly influencing ODA (Open Document Architecture), but there have not been pure-bred descendants with immaculate pedigree.

Although there was no "Ed Taft" for Interscript, through the years it has left its mark on SGML and XML. And this is where I would like to make my point. If a new standard language is proposed today, the inspiration should not come from Interpress but from Interscript.

Useful links: