Databases Ch 3

• Rows contain data about an entity
• Columns contain data about attributes of the entities
• All entries in a column are of the same kind
• Each column has a unique name
• Cells of the table hold a single value
• The order of the columns is unimportant
• The order of the rows is unimportant
• No two rows may be identical

some identifiable thing

• existing data
• development of new information systems
• redesign of existing databases

Attributes

Tuples (rhymes with "couples")

Table, Relation

Column, Attribute

Row, Tuple

the value of one or more attributes determines the value of another attribute

two or more attributes determine the value of another

the attribute that determines the value of another attribute or set of attributes

a determinant that determines all of the other columns in a relation

one of the candidate keys that is selected to as the primary means for finding rows in a table - one per table - can have one column or be composite

artificial column that is added to a table to serve as the primary key

a column or composite of columns that is the pirmary key of a table other than the one in which it appears

a statement that limits the values of the foreign key (ensures that the values of a foreign key match a valid value of a primary key)

• Deletion anomaly
• Insertion anomaly
• Update anomaly

Data Integrity Problems

when one row is deleted, then the structure of the table forces facts about multiple things to be lost

the structure of the table forces us to enter facts about two or more entities when we just want to enter facts about one

updating a table may create data inconsistency