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June 3, 2008

Recently, Facebook has released a considerable size of its platform code as open source, using the Common Public Attribution License (CPAL) for their main license usage requirements.

This is most likely new to many Linux and open-source developers, and before they jump into CPAL there are some important points they need to read and fully understand. As with any open source code, it's smart to fully evaluate and assess your rights BEFORE you start depending on the new platform. There are parts of CPAL's licensing terms that some developers may not agree to.

CPAL was initially developed by social enterprise wiki company SocialText, and approved by the OSI in late 2007. Since then it has not seen wide adoption, although it is used by some prominent open-source projects, including the xTuple ERP applications and the Mule ESB.

CPAL is based on the familiar Mozilla Public License (used by Firefox, among other high-profile pieces of software) with two key modifications. First, CPAL includes an attribution requirement. Software licensed under the CPAL may include an exhibit with information about the original developer. This exhibit specifies that each time an Executable and Source Code or a Larger Work is launched or run, a prominent display of the Original Developer's Attribution Notice (as defined below) must occur on the graphic user interface (which may include display on a splash screen).

In the case of Facebook's open source code, the CPAL requires the display of this information:

Attribution Copyright Notice: Copyright © 2006-2008 Facebook, Inc.

Attribution Phrase: Based on Facebook Open Platform

Attribution URL: http://developers.facebook.com/fbopen

Graphic Image as provided in the Covered Code: http://developers.facebook.com/fbopen/image/logo.png

While to some people this may seem reasonable to recognize the work of Facebook developers, it does act as a sort of poison pill to prevent others from simply cloning Facebook on to their own sites, at least, others who don't want to give prominent credit to a rival.

The other difference between the MPL and the CPAL is in section 15, which closes the ASP loophole:

The term 'External Deployment' means the use, distribution, or communication of the Original Code or Modifications in any way such that the Original Code or Modifications may be used by anyone other than You, whether those works are distributed or communicated to those persons or made available as an application intended for use over a network.

This simply means that, if someone builds a web site based on the Facebook code, they must make the source code of their modifications available as soon as they let users into the site - whether or not they ship their own site code as a separate product!

One further note about CPAL: because it's based on the MPL, it is NOT compatible with the GPL. Facebook doesn't appear to have availed itself of the dual-licensing provisions of the CPAL, meaning that any of Facebook's CPAL-licensed code cannot legally be linked with GPL code.

Source: OS Tactic.

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