SQL SERVER Questions And Answers 1. What is an Entity? The basic data item stored in database is called entity. An entity can be any object, item, place, person, concept, or activity about which data is stored. 2. What is an attribute? An attribute is a property of an entity. It describes a part of an entity. Entity could have one or more attributes. 3. What is ER diagram? An Entity Relationship Diagram is diagrammatic representation of the logical structure of a database system. 4. Describe the concept of keys. Candidate key An attribute that uniquely identifies a row is called candidate key. It is also called das surrogate key. Primary key A candidate key that you choose to identify rows uniquely is called a primary key. Alternate key If there are multiple candidate keys in a table, the candidate keys that are chosen as primary key are called the alternate keys. Composite key When the key that uniquely identifies the rows of a table is made up of more than one attribute, it is ca...