What is an EDT, Base Enum, how can we use array elements of an EDT?

            EDT - To reuse its properties. The properties of many fields can change at one time by changing the properties on the EDT. Relations can be assigned to an edt are known as Dynamic relations.
EDT relations are Normal and Related field fixed.Why not field fixed – field fixed works on only between two tables 1- 1 relation. And Related field fixed works on 1- many tables.so edt uses related field fixed.

            BaseEnum - which is a list of literals. Enum values are represented internally as integers. you can declare up to 251 (0 to 250) literals in a single enum type. To reference an enum in X++, use the name of the enum, followed by the name of the literal, separated by two colons . ex -NoYes::No.