Re: GetHistory API RFC

Thanks for the feedback, Andy.  My comments inline:


On Wed, Apr 9, 2014 at 1:06 PM, andy@cx3marketing.com <andy@cx3marketing.com
> wrote:

> While I'm on a roll :-) ...
>
> I don't disagree with the value of having history--it can be very useful,
> especially if there's a consistent way to provide access to it.
>
> My concern with GetHistory was always that it assumes the system is
> logging *everything*. That's an unreasonable load, IMHO, especially
> since some CAN parameters will require an active request, potentially
> leading to an implementation flooding the CAN bus to acquire data that may
> never be used.
>
>
If the data is only being read from the bus and then logged by the system
there should be no flooding.  In the case where data is logged in an EDR
(Event Data Recorder)[1] and then broadcast over the bus on request, there
could be a problem with flooding, but system integrators can mitigate that
issue with caching and throttling (ie only allowing a certain number of
requests within a certain time frame).  This API, IMHO, is more complete
and hopefully addresses the concern over the ambiguity of logged data.


> What about if the application informs the system layer which bits of
> history it cares about? The assumption can be that no data will be
> logged unless you call something like <myclass>.enableHistory() first. And
> of course you can later .disableHistory(). This addresses the concern
> of overloading the embedded system and CAN bus with collecting unneeded
> data.
>
>
There is the potential that a system that logs too much can become
overloaded.  I think we should include and document the assumption that
certain data will already be logged regardless of whether or not an
application wants it.  This may because an OEM wants the data, the dealer
wants it, or even because of legal reasons[2].  In the latter case, there
has even been proposed legislation that requires this data to be accessible
by 3rd parties.  This API would fulfill that requirement[3].  Therefore, a
enable() or disable() method would not be necessary since the data will be
logged regardless.

-Kevron

[1] - https://en.wikipedia.org/wiki/Event_data_recorder
[2] - http://www.wired.com/2012/05/congress-black-box/
[3] -
http://www.roadandtrack.com/go/news/new-technology/event-data-recorders



> --Andy
>
>
> ___________________________________________
> Andy Gryc | Co-founder
> M: +1 613.618.8730 | E: andy@cx3marketing.com <nyoung@cx3marketing.com>
> W: www.cx3marketing.com
>
> On Apr 9, 2014, at 3:52 PM, Rees, Kevron <kevron.m.rees@intel.com> wrote:
>
> The purpose of GetHistory is to allow application to get stored
> information from the system without having to perform logging
> themselves.  Having the system provide data logging avoids the problem
> of having multiple applications logging the same data.
>
> Being able to retrieve logged data allows for some interesting
> features.  There are a number of projects that log and do neat things
> with vehicle data[1].
>
> This API will come with the assumption that the system will determine
> what data is stored, how often and how far back in time data will be
> available.
>
> This API may have one flaw however in that it may be processor
> intensive to do huge queries and pass that data to web applications.
> If we want to avoid that, we may want change the API with that in
> mind.
>
> It is also possible we can offer this API as an appendix to our
> vehicle data specification.
>
> [1] - http://icculus.org/obdgpslogger/
>
> interface HistoryItem {
>  readonly attribute any value;
>  readonly attribute DOMTimeStamp timeStamp;
> }
>
> callback GetHistoryCallback = void callback(HistoryItem[] items);
>
> partial interface VehicleInterface {
>  Promise getHistory(Date begin, Date end, optional Zone zone);
>  readonly attribute boolean isLogged;
>  readonly attribute Date from;
>  readonly attribute Date to;
>  readonly attribute short rate; // µHz
> }
>
> //check if there is data being logged for vehicleSpeed:
> if(vehicle.vehicleSpeed.isLogged)
> {
>   /// get all vehicleSpeed from the beginning of time
>   vehicle.vehicleSpeed.getHistory(new Date(0), new Date).then(
> function ( data ) {
>    console.log(data.length);
>  });
>
>  /// get all vehicleSpeed since it was first logged:
>
>  vehicle.vehicleSpeed.getHistory(vehicle.vehicleSpeed.from,
> vehicle.vehicleSpeed.to).then( function ( data ) {
>    console.log(data.length);
>  });
> }
>
> -Kevron
>
>
>