The HDF5 library stores data in individual "data sets" that can be single values, arrays, bitstreams, or tables. We will refer to these HDF5 data sets as "variables" to avoid confusion with the term "data set" as it applies to a numerical solution. Each variable has its own identifying name. The variables can be organized into "groups" to define a directory-like structure. Attributes can be created and associated with individual variables or groups. Attributes are generally used to explain the use of the array in question. HDF5 files are random access and have optional compression algorithms.

The generic data format will be referred to as XMDF (the Generic Modeling Data Format). The geometry formats (or types) supported will include 1D cross-sections, 1D meshes, 2D meshes, 2D grids, 3D meshes, and 3D grids. For the grids, we will support both cell-centered and mesh-centered grids and both Cartesian and curvilinear grids.