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Reduced Products of Abstract Domains for Fairness Certification of Neural Networks

Mazzucato, Denis; Urban, Caterina

The `16.tar.gz` archive represents the artifact submission for SAS 2021 tool-paper: Reduced Products of Abstract Domains for Fairness Certification of Neural Networks. It includes the compressed docker image `tool-16.tar.gz` alongside the `README.md` (reported below).

Reduced Products of Abstract Domains for Fairness Certification of Neural Networks

Nowadays, machine-learned software plays an increasingly important role in critical decision-making in our social, economic, and civic lives.

Libra is a static analyzer for certifying fairness of feed-forward neural networks used for classification of tabular data. Specifically, given a choice (e.g., driven by a causal model) of input features that are considered (directly or indirectly) sensitive to bias, a neural network is fair if the classification is not affected by different values of the chosen features.

When certification succeeds, Libra provides definite guarantees, otherwise, it describes and quantifies the biased behaviour. A preliminary version of Libra was developed to implement and test the analysis method described in:

  • C. Urban, M. Christakis, V. Wüstholz, F. Zhang - Perfectly Parallel Fairness Certification of Neural Networks. In Proceedings of the ACM on Programming Languages (OOPSLA), 2020.

Libra now additionally includes new abstract domains including a generic reduced product domain construction, a new auto-tuning mechanism for finding the optimal configuration for Libra’s forward pre-analysis, and a tasks scheduling optimization to leverage all the available CPUs for Libra’s backward analysis. These new features are described in:

  • D. Mazzucato, C. Urban - Reduced Products of Abstract Domains for Fairness Certification of Neural Networks. SAS2021 Proceedings, 2021.

# Getting Started

Please, note that inside the docker terminal Libra is ran by the `tool` command, this is due to double-blinded restrictions during the artifact submission. Libra is properly called `libra` whenever the tool is downloaded from the Libra repository.

## Docker Container

Here we show the instructions to run our container in Unix-based systems. In order to try Libra, `docker` is required.

First load the compressed docker image `tool-16.tar.gz` as follows (from within `tool-16.tar.gz` location):

docker load < tool-16.tar.gz

This command create the docker image `tool-16`. See all the docker images available in your host using

docker image ls

Then, run the container in an interactive session using

docker run -it tool-16

Note that, as soon as the process is finished, the container stops and everything inside of it is removed. Additionally, we already installed `nano` and `vim` inside the container to inspect and modify files.

Inside, the docker container is organized as follow:

/home # tool repository
├── src
│ └── tool
│ ├── abstract_domains # code
│ ├── core # code
│ ├── engine # code
│ ├── frontend # code
│ ├── semantics # code
│ ├── tests
│ │ ├── census
│ │ │ ├── logs1 # logs for experiment A
│ │ │ │ └── fetch.py # log fetch script
│ │ │ ├── logs2 # logs for experiment B
│ │ │ │ └── fetch.py # log fetch script
│ │ │ ├── logs3 # logs for experiment C
│ │ │ │ └── fetch.py # log fetch script
│ │ │ ├── 10.py # network with 10 ReLU
│ │ │ ├── 12.py # network with 12 ReLU
│ │ │ ├── 20.py # network with 20 ReLU
│ │ │ ├── 40.py # network with 40 ReLU
│ │ │ ├── 45.py # network with 45 ReLU
│ │ │ ├── census.txt # experiments specification file
│ │ │ ├── census.csv # original dataset
│ │ │ └── ...
│ │ ├── example.py # simple example network
│ │ ├── example.txt
│ │ ├── toy.py # another simple example network
│ │ ├── toy.txt
│ │ └── ...
│ ├── configurations.sh # experiment B
│ ├── cpus.sh # experiment C
│ ├── keras2python.py # keras to python conversion script
│ ├── models.sh # experiment A
│ └── ...
├── README.md # this file
└── ...

The code directories (cf. `abstract_domains`, `core`, `engine`, `frontend`, and `semantic`) contain the python code modules. The architecture of Libra is explained in Section 2 in the SAS2021 paper.

## Command Line Usage

Libra expects as input a ReLU-based feed-forward neural network in Python program format. This can be obtained from a Keras model using the script `keras2python.py` (within Libra's `src/tool/` folder) as follows:

python3.7 keras2python.py <model>.h5

The script will produce the corresponding `<model>.py` file. In the file, the inputs are named `x00`, `x01`, `x02`, etc.

A specification of the input features is also necessary for the analysis. This has the following format, depending on whether the chosen sensitive feature for the analysis is categorical or continuous:

| Categorical                      | Continuous                                                 |
| -------------------------------- | ---------------------------------------------------------- |
| number of sensitive features     | 1                                                          |
| list of the inputs, one per line | value at which to split the range of the sensitive feature |

The rest of the file should specify the other (non-sensitive) categorical features. The (non-sensitive) features left unspecified are assumed to be continuous.

For instance, these are two examples of valid specification files:

| Categorical | Continuous |
| ----------- | ---------- |
| 2           | 1          |
| x03         | x00        |
| x04         | 0.5        |
| 2           | 2          |
| x00         | x01        |
| x01         | x02        |

In the case on the left there is one unspecified non-sensitive continuous feature (`x02`).

To analyze a specific neural network run:

tool <specification> <neural-network>.py [OPTIONS]

The following command line options are recognized:

--domain [ABSTRACT DOMAIN]

Sets the abstract domain to be used for the forward pre-analysis.

Possible options for [ABSTRACT DOMAIN] are:

  •  boxes (interval abstract domain)
  •  symbolic (combination of interval abstract domain with symbolic constant propagation [Li et al. - Analyzing Deep Neural Networks with Symbolic Propagation: Towards Higher Precision and Faster Verification (SAS 2019)])
  • deeppoly (deeppoly abstract domain [Singh et al. - An Abstract Domain for Certifying Neural Networks (POPL 2019)])
  •  neurify (neurify symbolic relaxation [Wang et al. - Efficient Formal Safety Analysis of Neural Networks (NeurIPS 2018)])
  • boxes_deeppoly (product of boxes and deeppoly)
  • boxes_neurify (product of boxes and neurify)
  • deeppoly_symbolic (product of deeppoly and symbolic)
  • neurify_symbolic (product of neurify and symbolic)
  • deeppoly_neurify (product of deeppoly and neurify)
  • boxes_deeppoly_neurify (product of boxes, deeppoly, and neurify)
  • deeppoly_neurify_symbolic (product of deeppoly, neurify, and symbolic)

Default: symbolic

--lower [LOWER BOUND]

Sets the lower bound for the forward pre-analysis.

Default: 0.25

--min_lower [LOWER BOUND]

Sets the minimum lower bound for the (auto-tuning of the) forward pre-analysis.

Default: the value of the lower bound

--upper [UPPER BOUND]

Sets the upper bound for the forward pre-analysis.

Default: 2

--max_upper [UPPER BOUND]

Sets the maximum upper bound for the (auto-tuning of the) forward pre-analysis.

Default: the value of the upper bound

--cpu [CPUs]

Sets the number of CPUs to be used for the analysis.

Default: the value returned by cpu_count()

During the analysis, Libra prints on standard output which regions of the input space are certified to be fair, which regions are found to be biased, and which regions are instead excluded from the analysis due to budget constraints.

The analysis of the running example from the OOPSLA paper can be run as follows (from within Libra's `src/tool/` folder):

tool tests/toy.txt tests/toy.py --domain boxes --lower 0.25 --upper 2

Another small example can be run as follows (again from within Libra's `src/tool/` folder):

tool tests/example.txt tests/example.py --domain boxes --lower 0.015625 --upper 4

The `tests/example.py` file represents a small neural network with three inputs representing two input features (one, represented by `x`, is continuous and one, represented by `y0` and `y1`, is categorical). The specification `tests/example.txt` tells the analysis to consider the categorical feature sensitive to bias. In this case the analysis should be able to certify 23.4375% of the input space, find bias in 71.875% of the input space, and leave 4.6875% of the input space unanalyzed. Changing the domain to any of the other options should analyze the entire input space finding bias in 73.44797685362308% of it. The input regions in which bias is found are reported on standard output.

# Step-by-Step Experiment Reproducibility

The experimental evaluation in the SAS paper was conducted on the CLEPS, a cluster machine with two 16-core Intel ® Xeon ® 5218 CPU @ 2.4GHz, 192GB of RAM, and running CentOS 7.7. with linux kernel 3.10.0.

## Experiment 1: Effect of Neural Network Structure on Precision and Scalability

To reproduce the results shown in Table 1 one can use the script `models.sh` within Libra's `src/tool/` folder.

./models.sh

The script will generate the corresponding log files in Libra's `src/tool/tests/census/logs1`. These can be manually inspected or a table summary of them can be generated using the script `fetch.py` in Libra's `src/tool/tests/census/logs1` folder.

Please take note of the expected execution times before launching the script. On a less powerful machine than that used for our evaluation it might be preferable to comment out the most time consuming lines from the script before launching it.

## Experiment 2: Scalability-vs-Precision Tradeoff

To reproduce the results shown in Table 2 one can use the script `configurations.sh` within Libra's `src/tool/` folder.

./configurations.sh

The script will generate the corresponding log files in Libra's `src/tool/tests/census/logs2`. These can be manually inspected or a table summary of them can be generated using the script `fetch.py` in Libra's `src/tool/tests/census/logs2` folder.

Please take note of the expected execution times before launching the script. On a less powerful machine than that used for our evaluation it might be preferable to comment out the most time consuming lines from the script before launching it.

## Experiment 3: Leveraging Multiple CPUs

To reproduce the results shown in Table 3 one can use the script `cpus.sh` within Libra's `src/tool/` folder.

./cpus.sh

The script will generate the corresponding log files in Libra's `src/tool/tests/census/logs3`. These can be manually inspected or a table summary of them can be generated using the script `fetch.py` in Libra's `src/tool/tests/census/logs3` folder.

Please take note of the expected execution times before launching the script. On a less powerful machine than that used for our evaluation it might be preferable to comment out the most time consuming lines from the script before launching it. Note also that this script requires 64 CPUs, modify the script to fit your available resources before running it.

In the `src/tool/tests/census` folder is also present the original dataset `census.csv` as well as the 5 trained neural networks (`10`, `12`, `20`, `40`, `45`).

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