Often it is desirable to treat a collection of data files as if they were a single dataset. Hyrax provides two different ways to do this: it enables data providers to define aggregations of files so those appear as a single dataset and it provides a way for users to send the server a list of files along with processing operations and receive a single amalgamated response.
In the first half of this appendix, we discuss aggregations defined by data providers. These aggregations use a simple mark-up language called NCML, first defined by Unidata as a way to work with NetCDF files. Both Hyrax and the THREDDS Data Server use NCML as a tool to describe how data files can be combined to aggregated data sets. In the second part of this appendix, we discuss user-specified aggregations. These aggregations currently use a new interface to the Hyrax server.