When a date value is converted between internal binary format and display or entry format, a pattern directs the conversion. When conversion is done automatically, the pattern comes from the environment variable DBDATE. When it is done with an explicit call to the rfmtdate(), rdefmtdate(), or USING functions, a pattern string is passed as a parameter. In any case, the pattern string (the format of the message) must include letters that show the location of the three parts of the date: 2 or 3 letters d; 2 or 3 letters m; and either 2 or 4 letters y.