Appendix C

Question 1

Entity Relationship Diagram ERD

Answer 1

A technique for documenting the relationship between entities in a database environment.

Question 2

Entity- Also called a table

Answer 2

Stores information about a person, place, thing, transaction, or event
–a customer is an entity and so is a merchandise item

Question 3

Attribute

Answer 3

Data elements associated with an entity.

–A customer entity can be described by attributes such as: customer number, first name, last name, street, city, state, zip, phone number

Question 4

There Are Several categories of attributes including: 4 total

Answer 4

1) Simple versus composite
2) Single-Valued versus multi-valued
3) Stored Values derived
4) Null-Valued

Question 5

Composite Attributes **

Answer 5

Can Be Divided into smaller sub parts, which represent more basic attributes that have their own meanings.

Example: Address – broken down into a number of sub parts, such as number, street, city, & state.

Question 6

Attributes that are not divisible into sub parts are called simple attributes. Such as age, gender,

Question 7

Single Valued Attribute

Answer 7

Means only having only a single value of each attribute of an entity at any given time.

Example: A CUSTOMER entity allows only once Telephone Number for each CUSTOMER.

Question 8

Multi-Valued Attribute

Answer 8

Means having the potential to contain more than one value for an attribute at any given time.

Question 9

TEST QUESTION****

An entity in a relational database cannot have multi-valued attributes. ***

Question 10

Relational Databases do not allow multi-valued attributes because the can cause problems:

Answer 10

1) Confuses the meaning of data
2) Significantly slow down searching
3) Place unnecessary restrictions on the amount of data that can be stored.

Question 11

Derived Attributes

Answer 11

Can be calculated using the value of another attribute (attribute that is used to derive the attribute is called a stored attribute)

-Derived attributes are not stored, but can be derived when needed from stored attributes.

Question 12

Null-Valued-Attribute

Answer 12

Assigned to an attribute when no other value applies or when a value is unknown.

Question 13

ONce the basic entities and attributes have been defined, the next task is to identify the relationships among entities.

Question 14

The Three Basic Types of relationships:

Answer 14

1) one-to-one
2) one-to-many
3) many-to-many

Question 15

Composite Entities

Answer 15

Entities that exist to represent the relationship between two other entities.

Example: There is a many-to-many relationship between an ITEM and ORDER. *An order can contain many items and over time, the same item can appear on many ORDERs.

Question 16

Most database installations are based on the relational data models.

Answer 16

**8

Question 17

The word “table” is used synonymously with “entity”.

Question 18

A row and a relation has the following properties:

1) only one value at the intersection of a column and row- a relation does not allow multi-valued attributes.
2) Uniqueness-There are no duplicate rows in a relation
3) Primary Key - A field that uniquely identifies a given entity in a table

Question 19

Foreign Key

Answer 19

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