There is little need for all of this (sets, set notation, set membership, complements of sets,
set union, set intersection, cartesian products, cardinality of sets, and Venn Diagrams)
in most programming situations.
However, when working with a database, using SQL (Structured Query Language),
this material forms the basis for what one can do and for what one usually wants to do
with the database.
It is important to note the difference between a mathematical set
(duplicate values are not allowed and there is no importance to the position of an item
in the listing of a set)
and a list (duplicate values are allowed
and the position of the item in the list may be important).
Do not be "fooled" by someone calling something a data set, they almost certainly
mean a data list.