Re: definition of "unlinkable data" in the Compliance spec

Unlinkable data is data that cannot reasonably be associated with an identifiable person or user agent.

Lauren Gelman
BlurryEdge Strategies
415-627-8512

On Sep 18, 2012, at 8:05 AM, Ed Felten wrote:

> Sorry to repost this, but nobody has answered any of my questions about Option 1 for the unlinkability definition.   
> 
> Note to proponents of Option 1 (if any): If nobody can explain or clarify Option 1, that will presumably be used as an argument against Option 1 when decision time comes.
> 
> ---------- Forwarded message ----------
> From: Ed Felten <ed@felten.com>
> Date: Thu, Sep 13, 2012 at 5:03 PM
> Subject: definition of "unlinkable data" in the Compliance spec
> To: "<public-tracking@w3.org>" <public-tracking@w3.org>
> 
> 
> I have some questions about the Option 1 definition of "Unlinkable Data", section 3.6.1 in the Compliance spec editor's draft.   The definition is as follows [fixing typos]:
> 
> A party renders a dataset unlinkable when it: 
> 1. takes commercially reasonable steps to de-identify data such that there is confidence that it contains information which could not be linked to a specific user, user agent, or device in a production environment
> [2. and 3. aren't relevant to my questions]
> 
> I have several questions about what this means.
> (A) Why does the definition talk about a process of making data unlinkable, instead of directly defining what it means for data to be unlinkable?  Some data needs to be processed to make it unlinkable, but some data is unlinkable from the start.  The definition should speak to both, even though unlinkable-from-the-start data hasn't gone through any kind of process.  Suppose FirstCorp collects data X; SecondCorp collects X+Y but then runs a process that discards Y to leave it with only X; and ThirdCorp collects X+Y+Z but then minimizes away Y+Z to end up with X.  Shouldn't these three datasets be treated the same--because they are the same X--despite having been through different processes, or no process at all?  
> (B) Why "commercially reasonable" rather than just "reasonable"?  The term "reasonable" already takes into account all relevant factors.  Can somebody give an example of something that would qualify as "commercially reasonable" but not "reasonable", or vice versa?  If not, "commercially" only makes the definition harder to understand.  
> (C) "there is confidence" seems to raise two questions.  First, who is it that needs to be confident?  Second, can the confidence be just an unsupported gut feeling of optimism, or does there need to be some valid reason for confidence?  Presumably the intent is that the party holding the data has justified confidence that the data cannot be linked, but if so it might be better to spell that out.
> (D) Why "it contains information which could not be linked" rather than the simpler "it could not be linked"?  Do the extra words add any meaning?
> (E) What does "in a production environment" add?  If the goal is to rule out results demonstrated in a research environment, I doubt this language would accomplish that goal, because all of the re-identification research I know of required less than a production environment.  If the goal is to rule out linking approaches that aren't at all practical, some other language would probably be better.
> 
> (I don't have questions about the meaning of Option 2; which shouldn't be interpreted as a preference for or against Option 2.)
> 
>