ribed by
one or more chunk(s). The current model allows for a linear sequence of named parts within an
artifact; this works for some aggregations (e.g. flat tar or zip files) and linear data file formats 
(e.g. FITS) but is not well-suited to hierarchical structures (e.g. directory structures, HDF). 
A chunk is able to describe astronomical data arrays (e.g. spectra, images, cubes), but
cannot describe arbitrary data structures like lists of data objects or tabular data.</p>

<p>The data access parts of the