The concept of a standard flexible format for the transfer of astronomical data was so appealing that astronomical software designers sought to apply the format to data and information structures other than simple arrays. For example, astronomers make extensive use of catalogs. Such information would most naturally be stored as a table. The wide variety of tabular information led to the development of the ASCII table extension. The following three main classes of potential applications were envisioned:
The ASCII table FITS extension (Harten et al. 1988; hereafter FITS Paper IV) conforms to the standard FITS rules and to the generalized rules for FITS extensions. The column headings are provided in an extension header that describes the contents of the table. The table data are stored as a large character array. Each row of the table consists of a sequence of fields. Each field is described by a series of keywords specifying the field format using FORTRAN-77 notation, the location in the row where it begins, and possibly a column heading or other information about the field.