DBMS Database Management System - Technical Questions and Answers

DBMS - Database Management System
DBMS - Basics

21.	Explain the relationship between entity, entity class, and entity instance.
	Answer: An entity is something that can be identified in the users' work environment, something that the users want to track. Entities of a given type are grouped into entity classes. An entity instance is the representation of a particular entity. Workspace Report errors ... Name : Email: View Answer

22.	Explain the difference between attributes and identifiers.
	Answer: Entities have attributes. Attributes are properties that describe the entity's characteristics. Entity instances have identifiers. Identifiers are attributes that name, or identify, entity instances. Workspace Report errors ... Name : Email: View Answer

23.	Name and describe three types of binary relationships.
	Answer: 1:1 - a single entity instance of one type is related to a single-entity instance of another type. 1:N - a single entity instance of one type is related to many-entity instances of another type. M:N - many-entity instances of one type relate to many-entity instances of another type. Workspace Report errors ... Name : Email: View Answer

24.	What is the archtetype/instance pattern?
	Answer: The archetype/instance pattern occurs when one entity tracks occurrences of another entity. A common example is the relationship between CLASS and SECTION, where the actual occurrence of a class happens when students register for a SECTION of that CLASS. The archetype/instance pattern is implemented as an ID-dependent relationship. Workspace Report errors ... Name : Email: View Answer

25.	What is a recursive relationship? Give an example not used in the text.
	Answer: A recursive relationship is a relationship between an entity and itself. For example, given the entity PERSON, a recursive relationship could be used to show a PERSON and his or her SIBLINGs (brothers and sisters). Workspace Report errors ... Name : Email: View Answer

26.	What are the steps for transforming an entity into a table?
	Answer: The steps are: (1) specify the primary key, (2) specify candidate keys, (3) specify column properties including null status, data type, default value (if any), and data constraints (if any), and (4) verifying normalization. Workspace Report errors ... Name : Email: View Answer

27.

Define a surrogate key, describe the ideal primary key and explain how surrogate keys meet this ideal.

28.

Define and discuss data constraints.

29.

In general, how are recursive relationships handled in a database design?

30.

What is a cascading update?