Hi Xiangdong,
to your second question:
The use case ist he other way round.
We know that we measure e.g. a voltage between 3V and 4.2V with a precision of
0.01 or something.
Then its most efficient to store integers and a formula like a * x + b with
e.g. b = 3 and a = 1/100.
So 3V would be stored as x = 0, 3.01V -> x = 1, ... 4.2V as x = 1200.
So we only store 0 to 1200 and no decimals and stuff which would be very easily
compressable I thnk.
Julian
Am 29.10.19, 07:13 schrieb "Xiangdong Huang" <saint...@gmail.com>:
Hi,
> In Java we could model it as a variable Optional<> x which could be null,
Optional.empty(), Optional.of(true), Optional.of(false).
It make sense. And, using a new data type to achieve in IoTDB it is ok.
> Or scale formulas like a*x+b which allows to leverage the precision even
for “small” double values or even integers.
So, are you considering a use case like: the time series value should be
[1, 1, 0, 0, 1, 1, 1, 0, 0...] but actually we get [0.99, 0.99, 0.01, 0,
1, 1, 0.999, 0, 0.01] (because of the precision of sensors)?
And, what values do you want to save?
(1)save them as 1 and 0. Or,
(2) save them as 0.99, 0.01 indeed, but using a specific query API to
return data like 1 and 0?
My another question is, is there a general data type can support the above
cases?
Best,
-----------------------------------
Xiangdong Huang
School of Software, Tsinghua University
黄向东
清华大学 软件学院
Julian Feinauer <j.feina...@pragmaticminds.de> 于2019年10月29日周二 上午3:58写道：
> Hi all,
>
> I wanted to discuss a possible new feature I will call Rich Datatypes
> (RDT) API in the following.
> I worked a lot in the automotive industry and there is a broadly adopted
> open Standard called ASAM MDF (https://www.asam.net/standards/detail/mdf/
> ).
> It is a format which is targeted at the efficient storage but at the same
> time it supports VERY complex types (which are often used in automotive
> controllers).
>
> Take something as simple as a boolean. We could store it as a boolean (as
> java bool) in 1 bit.
> BUT we have overall 4 possibilities:
>
> * No value is available for a timestamp (NULL / nothing stored)
> * We had a successful request but the Controller does not know whether
> true or false (or had an internal error), this is a bit like
> Optional.isPresent() == false
> * True
> * False
> In Java we could model it as a variable Optional<> x which could be null,
> Optional.empty(), Optional.of(true), Optional.of(false).
>
> Other examples are discrete values like “ON”, “OFF” (which are handled as
> “lookup tables” on integer rows, internally).
> Or scale formulas like a*x+b which allows to leverage the precision even
> for “small” double values or even integers.
> A formula but also a “fallback” lookup value like “NV”.
>
> I think this could be a valuable extension to IoTDB as an additional API
> (not change anything below but just provide an API on top to do the
> calculation).
>
> What do others think?
>
> Julian
>
