Anomaly Detection in Multi-Level Model Space

Anomaly detection (AD) is gaining prominence, especially in situations with limited labeled data or unknown anomalies, demanding an efficient approach with minimal reliance on labeled data or prior knowledge. Building upon the framework of Learning in the Model Space (LMS), this paper proposes conducting AD through Learning in the Multi-Level Model Spaces (MLMS). LMS transforms the data from the data space to the model space by representing each data instance with a fitted model. In MLMS, to fully capture the dynamic characteristics within the data, multi-level details of the original data instance are decomposed. These details are individually fitted, resulting in a set of fitted models that capture the multi-level dynamic characteristics of the original instance. Representing each data instance with a set of fitted models, rather than a single one, transforms it from the data space into the multi-level model spaces. The pairwise difference measurement between model sets is introduced, fully considering the distance between fitted models and the intra-class aggregation of similar models at each level of detail. Subsequently, effective AD can be implemented in the multi-level model spaces, with or without sufficient multi-class labeled data. Experiments on multiple AD datasets demonstrate the effectiveness of the proposed method.