Classifier chains for multi-label classification
J. ReadBernhard PfahringerG. HolmesE. Frank
Proposes classifier chains and ensemble extensions that model label correlations in multi-label classification while retaining the computational efficiency and linear scalability of binary relevance across large datasets.
Multi-label classification assigns multiple labels to each instance and arises in text categorization, scene analysis, and bioinformatics. The binary relevance method treats each label independently and scales linearly with the number of labels, yet it is widely dismissed because it ignores correlations among labels. More elaborate methods that attempt to capture those correlations incur quadratic or exponential costs and often become intractable once the number of labels or training examples grows large.
The article introduces classifier chains, a problem-transformation technique that retains the linear complexity of binary relevance while propagating label information along an ordered sequence of binary classifiers. Each classifier receives the original features plus the 0/1 predictions of all preceding classifiers in the chain, thereby modeling label dependence at modest extra cost. An ensemble of such chains, each with a random label order and trained on bootstrap samples, further improves robustness; a lightweight variant that randomly subsamples both attributes and instances makes the ensemble practical for very large data.
Extensive experiments on fifteen datasets ranging from a few hundred to more than one hundred thousand examples and up to nearly one thousand labels show that the single-chain method already surpasses binary relevance and related stacking approaches on most accuracy-oriented measures. The full ensemble matches or exceeds the predictive performance of far more complex state-of-the-art algorithms while finishing training and testing in a fraction of the time; on the largest collections only the binary-relevance family completes within reasonable resource limits. Subsampling reduces running time dramatically with negligible loss in accuracy.
These results indicate that carefully designed binary-relevance methods can deliver high accuracy at low cost and therefore deserve renewed consideration for production-scale multi-label tasks. Practitioners facing large label sets or streaming data should therefore prototype an ensemble of classifier chains, optionally with attribute and instance subsampling, before investing in more elaborate correlation-modeling schemes. Further work is warranted on adaptive chain ordering and on threshold calibration when label cardinality differs markedly between training and test distributions.
- Paper: In Defense of One-Vs-All Classification, Ryan Rifkin et al. (2004). This paper provides foundational empirical justification for one-vs-all binary decomposition, which serves as the core baseline and structural building block that classifier chains directly adapt and extend.
- Paper: BoosTexter: A Boosting-based System for Text Categorization, ROBERT E. SCHAPIRE et al. (2000). BoosTexter establishes the formal formulation and benchmark evaluation standards for multi-label text categorization problems addressed by classifier chains.
- Paper: Large Margin Methods for Structured and Interdependent Output Variables, Ioannis Tsochantaridis et al. (2005). This work introduces structured output learning to model interdependencies among outputs, providing the theoretical context for modeling label correlations that classifier chains solve with lower computational complexity.
- Paper: The Random Subspace Method for Constructing Decision Forests, Tin Kam Ho (1998). Tin Kam Ho introduces feature-subspace randomization in ensemble learning, which directly underlies the random attribute and instance subsampling strategies used in ensembles of classifier chains.
- Paper: Random Forests, Leo Breiman (2001). Breiman's bagging and feature-subspace ensemble principles form the methodological foundation for constructing robust ensembles of classifier chains.
- Paper: On Combining Classifiers, Josef Kittler et al. (1998). This paper establishes formal Bayesian fusion and voting rules for combining outputs from multiple diverse classifiers, which ensembles of classifier chains leverage during inference.
- Paper: Solving Multiclass Learning Problems via Error-Correcting Output Codes, Thomas G. Dietterich et al. (1994). Dietterich and Bakiri present output coding transformations that decompose multi-output problems into binary learners, serving as an important conceptual precursor to chain transformations.
- Paper: A Review on Multi-Label Learning Algorithms, Min-Ling Zhang et al. (2014). This comprehensive review places classifier chains within the broader taxonomy of high-order problem-transformation methods and evaluates their algorithmic complexity against subsequent multi-label learning paradigms.
