This hierarchy provides the code structure of the MetricOverlay plugin for Eclipse. It is designed to provide an extensible model that can provide augmentations into the Eclipse's Java Editor (JDT). The data from these augmentations is derived from metrics, which are mapped onto augmentations using an interpolation mechanism. The system supports an API and XML input. The system utilises existing Eclipse functionality by providing a table view of mappings and a set of preference pages to allow user specifications to be changed.