lec 2

Question 1

database schema

Answer 1

the set of all schema for a given database

Question 2

Relational database naming properties

Answer 2

• tables get names distinct from other names in database’s schema
• within a table each attribute has distinct name
• across tables, same attribute names should refer to the same thing

Question 3

Relational database ordering properties

Answer 3

tables not indexed arrays

• ordering of attributes has no significance
• ordering or records has no significance

Question 4

R. database content properties

Answer 4

• each record distnct(could never get to duplicate records)
• each cell of a table has exactly one atomic value
• the values of an attribute must all be from the same domain and of the same data type

Question 5

key

Answer 5

attribute or set of attributes that uniquely identifies records within a table

Question 6

candidate key

Answer 6

a key such that no proper subset is a key within the table

Question 7

primary key

Answer 7

attribute or set of attributes that is selected to identify records uniquely within a table

Question 8

alternate key

Answer 8

a candidate key that has not been selected as the primary key

Question 9

foreign key

Answer 9

an attribute or set of attributes within one table that matches the candidate key of some relation

Question 10

Nulls

Answer 10

represent a value for the record that is currently unknown or not applicable to this record, different from 0 or space

Question 11

entity integrity

Answer 11

no part of a primary key can be null

Question 12

referential integrity

Answer 12

foreign key must match a candidate key in it’s home table or all parts of the foreign key value must be null

Question 13

enterprise constraints

Answer 13

are additional rules specified by the user’s or database administrators of a database

Question 14

view

Answer 14

virtual record(derived from one or more records)

• may limit access to only part of a record
• may combine data from multiple related records
• may combine and limit access to data

Question 15

views that can update a database

Answer 15

those that are limited to individual records in a single table,
- not for views combining multiple records from one or more tables

Question 16

1:1 relationship

Answer 16

each employee has personal information, organizational information

• all data must be combined into a single database record
• multiple views can be used for subsets of the record

Question 17

1:n relationships

Answer 17

an attribute having multiple values

each value needs it’s own line

Question 18

n:1

Answer 18

multiple records have the same attribute(multiple sales slips for the same customer)
- use the customer record’s key as a foreign key in the sales slip record

Question 19

typical way of dealing with n:n

Answer 19

replace them with n:1 and 1:n relationships without introducing redundant data
create a view using the keys of both records