Section 5.3.5.1.4.1. Treatment of missing data

When a requested data item is absent from the CIF, QUASAR will nevertheless emit a data name with a corresponding value of ` ?', the conventional CIF value of null type for `unknown quantity'. A CIF comment is also generated by QUASAR to indicate that the entry was missing from the input CIF. If the missing data name is found between data names that have multiple values and that occur in the same looped list, it is assumed that the missing data name should be associated with the same looped list, and it will be emitted in the loop header; the integrity of the list is then satisfied by emitting a column of unknown values. Note how this behaviour differs from that of the generic STAR File extraction utility Star_Base (Spadaccini & Hall, 1994), which silently ignores missing data items. However, it is a useful behaviour for applications that depend on finding a specific data item in their processing stream, even where its value is unknown.