<database> Any attribute that can have multiple values
associated with a single instance of some entity. For
example, a book might have multiple authors.
Such a "-to-many" relationship might be represented in an
unnormalised relational database as multiple author columns
in the book table or a single author(s) column containing a
string which was a list of authors. Converting this to "first
normal form" is the first step in database normalisation.
Each author of the book would appear in a separate row along
with the book's primary key. Later nomalisation stages
would move the book-author relationship into a separate table
to avoid repeating other book attibutes (e.g. title,
publisher) for each author.
