Learn about 4NF and how it deals with multi-valued dependencies.
Fourth Normal Form (4NF) is a level of database normalization that goes beyond BCNF to address a different type of dependency called a multi-valued dependency. A table is in 4NF if it is in BCNF and has no multi-valued dependencies. A multi-valued dependency occurs when the presence of one row in a table implies the presence of one or more other rows in that same table. Specifically, for a dependency A →→ B (read as 'A multi-determines B'), it means that for each value of A, there is a well-defined set of values for B, and that set of values for B is independent of any other attributes in the table. This typically happens when a table tries to represent two independent many-to-many relationships in a single table. For example, imagine a table `Student_Club_Sport` with columns (`student_id`, `club`, `sport`). A student can join multiple clubs and play multiple sports. The clubs they are in are independent of the sports they play. This leads to redundancy, as you would need a row for every combination of that student's clubs and sports. For instance, if student 1 is in the Chess Club and Debate Club and plays Tennis and Soccer, you would need four rows: (1, Chess, Tennis), (1, Chess, Soccer), (1, Debate, Tennis), (1, Debate, Soccer). To bring this to 4NF, you would decompose it into two tables: `Student_Clubs` (`student_id`, `club`) and `Student_Sports` (`student_id`, `sport`), eliminating the multi-valued dependency.