What are PDS archives? What is a data set?

Planetary science data stored in PDS are organized by data sets. A data set is a collection of related data products, usually data products acquired by a particular instrument and processed in a certain way. Each data product within a data set is of a given product type and has a unique Product ID. The data set also includes all documentation and supporting materials needed to understand and use the data products. Data sets are stored in volumes.