Safe Semi-Supervised Learning of Sum-Product Networks

TL;DR

This paper introduces a safe semi-supervised learning method for Sum-Product Networks, enabling efficient, non-restrictive, and improved generative and discriminative modeling with unlabelled data.

Contribution

It presents the first semi-supervised learning approach for SPNs that guarantees performance improvement and combines generative and discriminative capabilities.

Findings

Safe semi-supervised learning with SPNs is competitive with state-of-the-art methods.

The approach can improve both generative and discriminative objectives.

It is computationally efficient and does not impose restrictive data assumptions.

Abstract

In several domains obtaining class annotations is expensive while at the same time unlabelled data are abundant. While most semi-supervised approaches enforce restrictive assumptions on the data distribution, recent work has managed to learn semi-supervised models in a non-restrictive regime. However, so far such approaches have only been proposed for linear models. In this work, we introduce semi-supervised parameter learning for Sum-Product Networks (SPNs). SPNs are deep probabilistic models admitting inference in linear time in number of network edges. Our approach has several advantages, as it (1) allows generative and discriminative semi-supervised learning, (2) guarantees that adding unlabelled data can increase, but not degrade, the performance (safe), and (3) is computationally efficient and does not enforce restrictive assumptions on the data distribution. We show on a variety of data sets that safe semi-supervised learning with SPNs is competitive compared to state-of-the-art and can lead to a better generative and discriminative objective value than a purely supervised approach.