DBMS: Second Normal Form (Definitions)

"The second normal form (2NF) requires that all attributes be dependent on the whole key. To attain 2NF, the entity must be in 1NF and every nonprimary attribute must be dependent on the entire primary key for its existence. 2NF further reduces possible redundancy in the data model by removing attributes that are dependent on part of the key and placing them in their own entity." (Claudia Imhoff et al, "Mastering Data Warehouse Design", 2003)

"A relation schema R is in 2NF if every nonprime attribute A in R is fully functionally dependent on the primary key of R." (S. Sumathi & S. Esakkirajan, "Fundamentals of Relational Database Management Systems", 2007)

"A table is in 2NF if it is in 1NF and every field that is not part of the primary key depends on every part of the primary key." (Rod Stephens, "Beginning Database Design Solutions", 2008)

"Data is said to be in the second normal form if it complies with the first normal form and has one or more columns in a table that uniquely identify each row." (Robert D. Schneider and Darril Gibson, "Microsoft SQL Server 2008 All-In-One Desk Reference For Dummies", 2008)

"A table is in second normal form (2NF) if and only if each non-key attribute (data item) is fully dependent on the primary key, that is either the left side of every functional dependency (FD) is a primary key or can be derived from a primary key." (Toby J Teorey, ", Database Modeling and Design" 4th Ed, 2010)

"In relational theory, the second of Dr. Codd’s constraints on a relational design: Each attribute must depend on the entire primary key." (David C Hay, "Data Model Patterns: A Metadata Map", 2010)

"The second stage in the normalization process in which a relation is in 1NF and there are no partial dependencies (dependencies in only part of the primary key)." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management" 9th Ed., 2011)

"An entity is in second normal form if and only if it is in first normal form and every non-key attribute is fully dependent on the key." (Craig S Mullins, "Database Administration", 2012)

"The second level of normalization for a table in a relational database. A table is in 2NF if:" (Rod Stephens, "Beginning Software Engineering", 2015)