Resource map. Each data model (i.e. 'Precursor') in miRMaid has resource URLs for listing all objects (/precursors) or a single object (/precursors/hsa-mir-21). Relationships (denoted by edges in the figure) between models are captured by nested resource URLs (/matures/hsa-miR-21/papers). A solid circle at the end of an edge denotes a 'many' relationship. For example, a species 'has many' precursors (/species/hsa/precursors), while a precursor is related to only 'one' species (/precursors/hsa-mir-21/species).