An important characteristic of a fractional design is the defining relation, which gives the set of interaction columns equal in the design matrix to a column of plus signs, denoted by "I". For the above example, since "D" = "AB" and "E" = "AC", then "ABD" and "ACE" are both columns of plus signs, and consequently so is "BDCE". In this case the defining relation of the fractional design is "I" = "ABD" = "ACE" = "BCDE". The defining relation allows the alias pattern of the design to be determined.