Chapter 5

Define Foreign key. What is this concept used for?

A primary key of one table that appears as an attribute in another table and acts to provide a logical relationship between the two tables

Why are tuples not ordered

A relation is defined as a set of tuples. In set theory, elements in a set has no order. Following this logic, tuples do not need to be ordered.

Why are duplicate tuples not allowed in a relation

A relation is defined as a set of tuples. Mathematically, elements of a set have no order among them; hence, tuples in a relation do not have any particular order.

Domain

A set of atomic values

What is the difference between a key and a superkey

A superkey is a set of attributes that are used to uniquely define each tuple in a relation. A key is a minimalistic superkey, meaning that removing any attribute in the key renders the attributes of the key not unique.

What is a transaction? How does it differ from an update operation?

A transaction is a program that deals database operations such as reading, deleting or updating the DB. An update solely is used to modify the database.

Discuss the entity integrity and referential integrity constraints. Why is each important?

Entity Integrity- no primary key can be NULL. Having this property enables us to correctly distinguish between tuples. Referential Integrity ensures consistency among tuples. This says that one tuple in a relation that refers to another relation refer to an existing tuple in that relation.

Why do we designate one of the candidate key to be a primary key?:

It becomes easier to deal with a database when we can have a single distinct key for a particular relation instead of having more than one key.

Discuss the characteristics of relations that make them different from ordinary tables and files

Ordering of tuples in a Relation -The tuples are not considered to be ordered, even though they appear to be in the tabular form. Ordering of attributes in a relation schema R and of values within each tuples - We consider the attributes in R(A1, A2, .., An) and the values in t=<v1, v2, .., vn> to be ordered. Values in a tuple - All values are considered to be indivisible(atomic). A special null value is used to represent values that are unknown or inapplicable to certain tuples.

relational schema

R(A1, A2, A3). Defines the Relation and attributes

relational database schema

Tables, columns, and relations that make up a relational database

Attribute

name of the role played by some domain D in the relation of R.

n Tuple

ordered list of values, where t= <v1, v2.. vi>, and each vi is an element of the Dom(Ai)

relational database state

set of relational states that satisfy the integrity constraints

degree of a relationship

the number of attributes in the relational schema

relation state

the relation state is a set of n tuples