Alex Swan
Mr. Davis
9/18/12
Homework Review Questions
3.1 Define the following terms as they apply to the relational model of data: Domain – Set of atomic (indivisible) values. Attribute – it describes a component of the database, such as a table or a field. N-tuple – in mathematics, an ordered set of n elements called its components or coordinates. Relation Schema – It is representation of database highlighting relationships that we have created. Relation State – set of tuples that have the same attributes. Degree of a relation – number of attributes n of its relation schema. Relational Database Schema – Tables, columns and relationships that make up a relational database. Relational database state – is a union of
Values can also be not available presently. It is possible to devise different codes for different meanings of NULL values. For all these reasons, the value are generally written as NULL values in relations.
3.8 Discuss the entity integrity and referential integrity constraints. Why is each considered important? - The entity integrity constraint states that no primary key value can be NULL and is considered to be very important. This is because the primary key value is used to identify individual tuples in a relation. Having NULL values for the primary key implies that we cannot identify some tuples. - The referential integrity constraint is specified between two relations and is used to maintain the consistency among the tuples in the two relations. Informally, it states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation. Example of a referential integrity constraint is a foreign key . If the referenced relation does not exist, it will lead in an invalid state of the database. It is considered equally important.
3.9 Define foreign key. What is this concept used for? - The concept of foreign key is mainly used to identify the different relationships between relations in a Relational Database Schema. By referencing, each relation in a database schema actually links itself to other relations through the referenced relation’s primary