1^st normal form rule: In the relational model, a column of a table must contain a single unstructured value.

students sid name class telephone enrollment lname fname cno major 1 Jones Allan 2 555-1234 101 No 108 Yes 2 Smith John 3 555-4321 105 No 3 Brown Harry 2 555-1122 101 Yes 108 No 5 White Edward 3 555-3344 102 No 105 No

• TABLE: Nested tables are singly dimensioned, unbounded collections of homogeneous elements.
• VARRAY: Varying length arrays like nested tables are also singly dimensioned collections of homogeneous elements. However, when you store and retrieve a VARRAY, its element order is preserved.

• natural modeling of one-to-many relationships,
• supporting aggregation as a type in the database, and
• supporting for ordered and unordered collections.

• Built-in datatypes,
• User-defined types, and
• References (REFs) to object types.