Input and output data is processed in the form of data sets, usually saved on disk as a FITS file. A data set can contain several blocks, such as tables and arrays (FITS's HDU).
Traditionally blocks in a data set have been addressed by number (their position in the data set). However the DAL allows the task programmer to address blocks by name, so that it would seem appropriate to ask that all blocks (extensions) have a name (that means the EXTNAME FITS key word is set), and that in a data set block names should be unique.
The OGIP conventions for data products all have the block name set, so it is a matter of extending this concept also to utility tasks that normally wouldn't bother with the extension name.
The OGIP HDUCLASS set of key words will be used. Possibly it will be necessary to extend the OGIP conventions to describe some other intermediate data set that may be produced during the interactive analysis.
