# Package Structure Overview

Tribuo has a modular structure to allow minimal dependencies for any specific deployment. We describe the overall package structure below.

## Package Description

The top level project has core modules which define the API, data interactions, a math library, and common modules shared across prediction types.

• Core - (artifactID: tribuo-core, package root: org.tribuo) Provides the main classes and interfaces:
• Dataset - A list of Examples plus associated feature information, such as the number of categories for categorical features, or the mean and variance in the case of real-valued features.
• DataSource - A list of Examples processed from some other format and accompanied by the provenance describing the source and processing of these Examples.
• Example - An array or list of String and value pairs. The Example is typed with a subclass of Output that represents the appropriate type of response.
• Feature - An immutable tuple of String and value. The String is the feature name, which is used as the feature’s unique identifier.
• FeatureMap - A map from String to VariableInfo objects. When immutable, it also contains feature id numbers, although these should be treated as an implementation detail and not relied upon.
• Model - A class that can make predictions of a specific Output type.
• Output - An interface denoting the type of output: regression, multi-label, multi-class, clustering, or anomaly detection.
• OutputInfo - An interface representing information about the output.
• Trainer - A class that generates Models based on a Dataset of a specific output type.
• Prediction - A class that stores the output of a Model when presented with an Example for labeling. It contains scores for each of the predicted labels. These scores may optionally be a probability distribution.
• VariableInfo - A class representing information about the feature, e.g., the number of times it occurred in the dataset.
• Core contains several other packages.
• dataset - Datasets which provide a view on another dataset, either subsampling it or excluding features below a threshold.
• datasource - Implementations of DataSource which operate on in-memory or simple on-disk formats.
• ensemble - Base classes and interfaces for ensemble models.
• evaluation - Base evaluation classes for all output types. This package also includes evaluation-related classes for cross-validation and train-test splitting.
• hash - An implementation of feature hashing which obfuscates any feature names that are stored in a Model. Hashing prevents feature names from leaking out of the training data.
• provenance - Provenance classes for Tribuo. Provenance tracks the location and transformations of datasets, the parameters of trainers, and other useful information.
• sequence - A sequence prediction API.
• transform - A feature transformation package that can be applied to a full dataset or to individual features matched via regexes. It also contains wrapping trainers (trainers that wrap another trainer to provide additional functionality) and wrapping models to ensure that the same transformations are always applied at prediction time.
• util - Utilities for basic operations such as for working with arrays and random samples.
• Data - (artifactID tribuo-data, package root: org.tribuo.data) provides classes which deal with sampled data, columnar data, csv files and text inputs. The user is encouraged to provide their own text processing infrastructure implementation, as the one here is fairly basic.
• columnar - The columnar package provides many useful base classes for extracting features from columnar data.
• csv - Builds on the columnar package and supplies infrastructure for working with CSV and other delimiter separated data.
• sql - Builds on the columnar package and supplies infrastructure for working with JDBC sources.
• text - Text processsing infrastructure interfaces and an example implementation.
• Json - (artifactID tribuo-json, package root: org.tribuo.json) provides functionality for loading from json data sources, and for stripping provenance out of a model.
• Math - (artifactID tribuo-math, package root: org.tribuo.math) provides a linear algebra library for working with both sparse and dense vectors and matrices.
• kernel - a set of kernel functions for use in the SGD package (and elsewhere).
• la - a linear algebra library containing functions used in the SGD implementation. It is not a full BLAS.
• optimisers - a set of stochastic gradient descent algorithms, including SGD with Momentum, AdaGrad, AdaDelta, RMSProp and several others. AdaGrad should be considered the default algorithm since it works best across the widest range of linear SGD problems.
• util - various util classes for working with arrays, vectors and matrices.

## Multi-class Classification

Multi-class classification is the act of assigning a single label from a set of labels to a test example. The classification module has several submodules:

Folder ArtifactID Package root Description
Core tribuo-classification-core org.tribuo.classification Contains an Output subclass for use with multi-class classification tasks, evaluation code for checking model performance, and an implementation of Adaboost.SAMME. It also contains simple baseline classifiers.
DecisionTree tribuo-classification-tree org.tribuo.classification.dtree An implementation of CART decision trees.
Experiments tribuo-classification-experiments org.tribuo.classification.experiments A set of main functions for training & testing models on any supported dataset. This submodule depends on all the classifiers and allows easy comparison between them. It should not be imported into other projects since it is intended purely for development and testing.
Explanations tribuo-classification-experiments org.tribuo.classification.explanations An implementation of LIME for classification tasks. If you use the columnar data loader, LIME can extract more information about the feature domain and provide better explanations.
LibLinear tribuo-classification-liblinear org.tribuo.classification.liblinear A wrapper around the LibLinear-java library. This provides linear-SVMs and other l1 or l2 regularised linear classifiers.
LibSVM tribuo-classification-libsvm org.tribuo.classification.libsvm A wrapper around the Java version of LibSVM. This provides linear & kernel SVMs with sigmoid, gaussian and polynomial kernels.
Multinomial Naive Bayes tribuo-classification-mnnaivebayes org.tribuo.classification.mnb An implementation of a multinomial naive bayes classifier. Since it aims to store a compact in-memory representation of the model, it only keeps track of weights for observed feature/class pairs.
SGD tribuo-classification-sgd org.tribuo.classification.sgd An implementation of stochastic gradient descent based classifiers. It includes a linear package for logistic regression and linear-SVM (using log and hinge losses, respectively), a kernel package for training a kernel-SVM using the Pegasos algorithm, and a crf package for training a linear-chain CRF. These implementations depend upon the stochastic gradient optimisers in the main Math package. The linear and crf packages can use any of the provided gradient optimisers, which enforce various different kinds of regularisation or convergence metrics. This is the preferred package for linear classification and for sequence classification due to the speed and scalability of the SGD approach.
XGBoost tribuo-classification-xgboost org.tribuo.classification.xgboost A wrapper around the XGBoost Java API. XGBoost requires a C library accessed via JNI. XGBoost is a scalable implementation of gradient boosted trees.

## Multi-label Classification

Multi-label classification is the task of predicting a set of labels for a test example rather than just a single label.

The independent binary predictor breaks each multi-label prediction into n binary predictions, one for each possible label. To achieve this, the supplied trainer takes a classification trainer and uses it to build n models, one per label, which are then run in sequence on a test example to produce the final multi-label output.

Folder ArtifactID Package root Description
Core tribuo-multilabel-core org.tribuo.multilabel Contains an Output subclass for multi-label prediction, evaluation code for checking the performance of a multi-label model, and a basic implementation of independent binary predictions.
SGD tribuo-multilabel-sgd org.tribuo.multilabel.sgd An implementation of stochastic gradient descent based classifiers. It includes a linear package for independent logistic regression and linear-SVM (using log and hinge losses, respectively) for each output label. These implementations depend upon the stochastic gradient optimisers in the main Math package. The linear package can use any of the provided gradient optimisers, which enforce various different kinds of regularisation or convergence metrics.

## Regression

Regression is the task of predicting real-valued outputs for a test example. This package provides several modules:

Folder ArtifactID Package root Description
Core tribuo-regression-core org.tribuo.regression contains an Output subclass for use with regression data, as well as evaluation code for checking model performance using standard regression metrics (R^2, explained variance, RMSE, and mean absolute error). The module also contains simple baseline regressions.
LibLinear tribuo-regression-liblinear org.tribuo.regression.liblinear A wrapper around the LibLinear-java library. This provides linear-SVMs and other l1 or l2 regularised linear regressions.
LibSVM tribuo-regression-libsvm org.tribuo.regression.libsvm A wrapper around the Java version of LibSVM. This provides linear & kernel SVRs with sigmoid, gaussian and polynomial kernels.
RegressionTrees tribuo-regression-tree org.tribuo.regression.rtree An implementation of two types of CART regression trees. The first type builds a separate tree per output dimension, while the second type builds a single tree for all outputs.
SGD tribuo-regression-sgd org.tribuo.regression.sgd An implementation of stochastic gradient descent for linear regression. It uses the main Math package’s set of gradient optimisers, which allow for various regularisation and descent algorithms.
SLM tribuo-regression-slm org.tribuo.regression.slm An implementation of sparse linear models. It includes a co-ordinate descent implementation of ElasticNet, a LARS implementation, a LASSO implementation using LARS, and a couple of sequential forward selection algorithms.
XGBoost tribuo-regression-xgboost org.tribuo.regression.xgboost A wrapper around the XGBoost Java API. XGBoost requires a C library accessed via JNI.

## Clustering

Clustering is the task of grouping input data. The clustering system implemented is single membership – each datapoint is assigned to one and only one cluster. This package provides two modules:

Folder ArtifactID Package root Description
Core tribuo-clustering-core org.tribuo.clustering Contains the Output subclass for use with clustering data, as well as the evaluation code for measuring clustering performance.
KMeans tribuo-clustering-kmeans org.tribuo.clustering.kmeans An implementation of K-Means using the Java 8 Stream API for parallelisation, along with the K-Means++ initialization algorithm.

## Anomaly Detection

Anomaly detection is the task of finding outliers or anomalies at prediction time using a model trained on non-anomalous data. This package provides two modules:

Folder ArtifactID Package root Description
Core tribuo-anomaly-core org.tribuo.anomaly Contains the Output subclass for use with anomaly detection data.
LibLinear tribuo-anomaly-liblinear org.tribuo.anomaly.liblinear A wrapper around the Java version of LibLinear, which provides a one-class SVM.
LibSVM tribuo-anomaly-libsvm org.tribuo.anomaly.libsvm A wrapper around the Java version of LibSVM, which provides a one-class SVM.

## Common

The common module shares code across multiple prediction types. It provides the base support for LibLinear, LibSVM, nearest neighbour, tree, and XGBoost models. The nearest neighbour submodule is standalone, however the rest of the submodules require the prediction specific implementation modules. The common tree package contains the implementations of Random Forests and Extremely Randomized Trees (ExtraTrees).

## Third party models

Tribuo supports loading a number of third party models which were trained outside the system (even in other programming languages) and scoring them from Java using Tribuo’s infrastructure. Currently, we support loading ONNX, TensorFlow and XGBoost models.

• ONNX - ONNX (Open Neural Network eXchange) format is used by several deep learning systems as an export format, and there are converters from systems like scikit-learn to the ONNX format. Tribuo provides a wrapper around Microsoft’s ONNX Runtime that can score ONNX models on both CPU and GPU platforms. ONNX support is found in the tribuo-onnx artifact in the org.tribuo.interop.onnx package which also provides a feature extractor that uses BERT embedding models.
• TensorFlow - Tribuo supports loading TensorFlow’s frozen graphs and saved models and scoring them.
Tribuo includes experimental support for TensorFlow-Java 0.3.1 (using TensorFlow 2.4.1) in the tribuo-tensorflow artifact in the org.tribuo.interop.tensorflow package. Models can be defined using TensorFlow-Java’s graph construction mechanisms, and Tribuo will manage the gradient optimizer output function and loss function. It includes a Java serialisation system so that all TensorFlow models can be serialised and deserialised in the same way as other Tribuo models. TensorFlow models run by default on GPU if one is available and the appropriate GPU jar is on the classpath.