Exam

Question 1

Data Redundancy

Answer 1

when data is stored in different places unnecessarily. E.g when you record names & numbers different places.

Question 2

Data Independance

Answer 2

Making changes to the way file characteristics are stored without affecting the programs ability to access data. e.g Usually lacking in file systems coz most programs change when data characteristics change.

Question 3

DBMS

Answer 3

Database Management System

Question 4

DBMS Functions

Answer 4

Eliminate data inconsistency, stop data anormaly, Data Dictionary Management, Data transformation, Security Management etc

Question 5

Structural Independance

Answer 5

When you can change the file structure without affecting the data access.

Question 6

Data

Answer 6

raw facts

Question 7

Information

Answer 7

Result of processing data to reveal meaning

Question 8

DBMS Role

Answer 8

A link between the user & the Database.
+s promotes data sharing, Eliminates problems islands of info, enforces data integrity,stops redundancy,promotes security

Question 9

Metadata

Answer 9

Data about data

Question 10

Spreadsheets cannot

Answer 10

Support self-doccumentation through metadata,enforcement of data types or domains to ensure consistency in columns, define relationships among tables, or constraints to make consistent on related tables.

Question 11

Data Modelling is important because

Answer 11

Designers use to communicate with programmers and end users of a database. Main function is understanding complexities of real world environment.

Question 12

A Business Rule

Answer 12

A short,precise and unambiguous description of a policy, procedure or principal that applies to an organization.

Question 13

Business Rule purpose

Answer 13

To define entities,attributes, relationships and constraints.

Question 14

Translating business rules

Answer 14

noun= entity verb= relationship between entities

Question 15

Relationship

Answer 15

Describes and association between entities

Question 16

Three types of relationships

Answer 16

1:M 1 to many, M:N Many to many, 1:1 one to one

Question 17

A Weak Entity must

Answer 17

1. Be existence dependant

2. The entity must have a PK that is partially or totally from the parent entity.

Question 18

Strong(or identifying) relationship

Answer 18

PK of related entities contains a PK component of parent entity. Shown bold line ERD

Question 19

Composite Entity

Answer 19

Is in a 1:M relationship with the parent entities and is made up of the pk attributes of the parent entity.
Used to represent/solve a M:N relationship between 2 or more entities.

Question 20

Recursive Relationship

Answer 20

when a relationship can exist between occurances of the same entity set. eg an employee is a manager of a store.

Question 21

Entity Supertype

Answer 21

A generic entity type that is related to one or more entity subtypes. Used to: avoid nulls when one supertype might have different characteristics than another.

Question 22

Example of 1:M Relationship

Answer 22

One cook can make many burgers and each burger can be made by many cooks.

Question 23

Example of M:N realtionship

Answer 23

A student can take many classes and each class can have many students.

Question 24

Example of 1:1 relationshiop

Answer 24

Each store is managed by one employee and each manager manages only one store.

Question 25

Logical independence

Answer 25

when you can change the internal model without affecting the conceptual model

Question 26

Physical independance

Answer 26

when you can change the physical model without affecting the internal model

Question 27

Difference between a database and a table

Answer 27

A database is made up of/holds tables and a table resembles a file conceptually.

Question 28

Entity Integrity

Answer 28

Each row (entity) in the table has its own unique identity(PK)

Question 29

referential Integrity

Answer 29

When the FK consists of a value that refers to an existing valid row in another relation.

Question 30

What subtypes store:

Answer 30

Unique attributes e.g if a supertype is employee subtypes could be cook,waitress bar man etc

Question 31

Specialization Hierachy

Answer 31

Shows the arrangment and relationships between entity supertypes and subtypes.

Question 32

Subtype Discriminator

Answer 32

The attribute in the supertype entity that detirmines which subtype the supertype is related to. E.g Employee type

Question 33

Overlapping subtypes

Answer 33

Contain nonunique subsets of the supertype entity each instance appearing in more than one subtype. e.g tech an employee can also be a student.

Question 34

Partial Completeness

Answer 34

Not every supertype occurance is a member of a subtype.

Question 35

Total Completeness

Answer 35

Every supertype occurance must be part of at least one subtype.

Question 36

Entity Cluster

Answer 36

a “virtual” entity type used to represent multiple entities and relationships in a erd. Simplifies erd and makes more readable.

Question 37

Surrogate PK

Answer 37

A Pk created by designer to simplify figuring out entities. Used when there is no natural suitable PK , when it is composite or too long to use.

Question 38

Fan Trap

Answer 38

Most common design trap. Happens when you have 1 entity in 2 1:M relationships and there is an association that is not expressed in the model. Doesn’t show relationship properly.

Question 39

Normalization

Answer 39

The process of evaluating and correcting table structures to minimize data redundancy and in turn reducing anomalies.

Question 40

1NF

Answer 40

Table format, no repeating groups, Pk identified, attributes dependent to PK still has partial dependencies.

Question 41

2NF

Answer 41

1NF and with no partial dependencies still might have transitive dependencies.

Question 42

Partial Dependancy

Answer 42

When an attribute is functionally dependant on only one part of a composite primary key. Associated with 1NF.