An early look at Portable Web Publications

PDF is the most popular document presentation format, but it’s primarily visual, letting you view or print a document the way it would originally have been printed. EPub focuses more on content, reflowing documents to fit screens of all sizes. The developers of the Open Web Platform think the next step should be documents that are equally at home offline and online. They’ve provided an idea (not yet a spec) of how this would work with the first Public Working Draft of Portable Web Publications.

This isn’t about defining a new format. It may result in a new archive format for bundling files, or it may use an existing one. For the most part, Portable Web Publications will use existing standards like HTML. The main new concepts are having a URI that can refer to a “document” consisting of multiple files, which can be downloaded as a self-contained unit, and allowing easy switching between online and offline modes. External dependencies aren’t excluded, but their absence should result in only minor degradation, such as text being presented in a usable alternate font.

We aren’t online all the time, or at least we don’t always have the bandwidth we’d like. Viewing a document repeatedly on a phone might run up excessive data charges, and sometimes an Internet connection isn’t available at all. The idea that’s presented is that a document could be downloaded to a device in a self-sufficient form, and the device would check for updates when it could. The Working Draft gives the example of a cockpit. (Maybe they should pick another example; the idea of a manual in a cockpit not always being up to date makes me nervous.)

Section 3.7 mentions the archival advantage of the proposed approach. When you archive a Web page, it may refer to an open-ended set of linked resources, which are linked to other resources, possibly encompassing most of the Web if you follow them exhaustively. A Portable Web Publication would delimit the resources that are necessary to an archival copy. It’s common for Web sites these days to pull in JavaScript and CSS from dozens of places. If they really need all those resources, they’re poor candidates for Portable Web Publications. Documents which are designed to be usable with only a local set of resources are much better prospects for archiving.

The goals of Portable Web Publications are strongly in line with EPub 3’s, but there’s a certain amount of discord:

Whilst the concept of Portable Web Publication is close to, and has been inspired by, EPUB 3, it goes beyond it, insofar as it emphasizes the need for a convergence between the offline and online usages. It would be highly desirable to deliver on the requirements on Portable Web Publications in an evolutionary manner that would build on, and would be backwards compatible with, existing EPUB 3, since the latter is already widely deployed. However, this may not be possible. …

The current evolution of EPUB 3 towards EPUB 3.1 will address several compatibility and convergence issues with the Open Web Platform; this will make the evolution path towards Portable Web Publications easier.

We’ll have to watch and see what happens.