Open hellais opened 2 months ago
Some work in progress on this front is being done on this branch: https://github.com/ooni/data/pull/85
In particular see the notebook which implements an early stage version of the bayes net: https://github.com/ooni/data/blob/bayes-net/oonipipeline/notebooks/web-analysis-bn.ipynb
There are still a few critical theoretical hurdles that need to be overcome, which are questions I would like to pose to people that have more experience about this, namely:
After more experimentation with the bayesian network approach and having a working PoC of it, I came to the conclusion that for the moment the performance of running this is not going to scale well to our use case without some significant work to re-engineer the analysis pipeline.
This lead to the conclusion that it was probably best for the time being to rollback to an approach that's simpler and closer to what we had done before, by using a fuzzy logic rule-based style classifier. Put in simpler terms this is just a list of IF THEN clauses that lead to the confidence estimates we have in a particular outcome being true. Through these we are effectively encoding the knowledge we have about certain signals in the measurements being a sign of blocking or not blocking.
In terms of implementation it's done directly as SQL queries which has the benefit of both being more performant than having to carry data in and out of python, but also allows to inspect and update the rules more easily as they all live in one place.
Work related to this is done inside of the following PR: https://github.com/ooni/data/pull/99, specifically the web_analysis.py
contains the mega-sql query to perform the analysis.
I will be following up with some more extensive documentation explaining how this whole system works.
Currently experiment results are semi-manually coded using bayesian style reasoning to come up with the weights.
It's however possible to do this using a more rigorous approach that makes use of well established graph based modeling systems such as bayesian networks.
Work on this has started already since a few months and had a very fruitful conversation about this topic with Joss who provided key insight.
As part of this activity the plan is to move this forward by doing some more modeling using bayes networks and see how it works.
Some sub-activities as part of this might include: