ERD

What are the Properties of Candidate key:

* It must contain unique values * Candidate key may have multiple attributes * Must not contain null values * It should contain minimum fields to ensure uniqueness * Uniquely identify each record in a table

What are the Rules for defining Primary key:

* Two rows can't have the same primary key value * It must for every row to have a primary key value. * The primary key field cannot be null. * The value in a primary key column can never be modified or updated if any foreign key refers to that primary key.

What are the properties of a foreign key?

* When more than one combination of attributes uniquely identify a row, they are called candidate keys e.g. I have a PPS# and CITStaffId * One candidate key is designated the primary key, others are termed alternate keys. Candidate keys are unique but also minimal in that they cannot be reduced. * If we find a candidate key occurring somewhere else in the database then it can be used as a relationship. We call this a candidate to foreign key link

Define the two principal integrity rules for the relational model.

1. Entity Integrity: (Applies Primary Key)in a base relation, no attribute of a primary key can be null. 2. Referential Integrity: The control of relationships in a database. There can be no unmatched foreign key values.

What is a Primary Key?

A column or group of columns in a table which helps us to uniquely identifies every row in that table is called a primary key. This DBMS can't be a duplicate. The same value can't appear more than once in the table.

What is a Foreign Key?

A foreign key is a column which is added to create a relationship with another table. Foreign keys help us to maintain data integrity and also allows navigation between two different instances of an entity. Every relationship in the model needs to be supported by a foreign key.

What is a Candidate Key?

A super key with no repeated attribute is called candidate key. The Primary key should be selected from the candidate keys. Every table must have at least a single candidate key.

What is the Alternate key?

All the keys which are not primary key are called an alternate key. It is a candidate key which is currently not the primary key. However, A table may have single or multiple choices for the primary key.