Exercises

1
Exercises

• Introduction to DatabasesDatabase Management
  Systems (DBMS)Relational Data Model
  
• Module CS6003
• Lecturer Roberto Rossi
• Feb - 2008

2
Exercises

• A DBMS is
• an information system
• a computerized system
• a set of data
• none of the former answers

3
Exercises

• Raw data stay
• at the bottom of the value scale
• at the top of the value scale
• above processed data in the value scale
• none of the former answers

4
Exercises

• A DBMS user
• designs the DB
• requires knowledge of the data model employed by
  the DBMS
  
• manages data stored in a DBMS
• none of the former answers

5
Exercises

• A DB is
• a collection of data
• a software application
• a file
• none of the former answers

6
Exercises

• In order to execute operations in a DBMS we need
  to
  
• write a software application
• write instructions in a language supported by the
  DBMS
  
• always contact the DBMS administrator
• none of the former answers

7
Exercises

• Why do we share data in companies
• to increase redundancy
• to reduce redundancy
• to find inconsistencies
• none of the former answers

8
Exercises

• From users viewpoint a DB is a collection of
  data that models
  
• the real world
• a portion of the reality of interest
• raw data
• none of the former answers

9
Exercises

• a data model is
• a collection of concepts used to describe data
• a hierarchical model
• an object model
• none of the former answers

10
Exercises

• The model shown in the picture is
• Hierarchical
• Network
• Relational
• none of the former

Ferrari
Todt
Shumacher
Barrichello
11
Exercises

• In a relational model Tables represent
• relations
• objects
• attributes
• none of the former answers

12
Exercises

• D1 a,b,c, D2 1,2 D1 x D2
• (a,1),(b,1),(b,2),(c,1),(c,2)
• (a,1),(a,2),(b,1),(c,1),(c,2)
• (a,1),(a,2),(b,1),(b,2),(c,1),(c,2)
• none of the former answers

13
Exercises

• The part of the table indicated by the arrow is
• The schema of the relation
• The instance of the relation
• The header of the relation
• None of the former answers

League
14
Exercises

• What is t?
• an attribute
• an instance
• a tuple
• none of the former answers

League
t
15
Exercises

• key constraints
• forbid that distinct tuples take the same value
  on one or more attributes
  
• state that distinct tuples take the same value on
  one or more attributes
  
• state which distinct tuples take the same value
  on one or more attributes
  
• none of the former answers

16
Exercises

• the set of all the attributes of the schema is
  always
  
• a superkey of R(X)
• a key of R(X)
• a tuple of R(X)
• none of the former answer

17
Exercise (complex)

• Design a simple relational DB with two tables
  modeling the following reality of interest
  
• We want to store in Table CUSTOMERS the set of
  customers of a DVD rental shop. Each customer is
  identified by a unique ID, for each customer we
  store Name, Surname and Date of Birth.
• We also want to store, in a separate Table called
  DVD, the list of DVDs rented by each user.
  Therefore in such a table we will memorize the
  Name of the movie, the Date in which it was
  rented, and the Customer that rented it.
• Once the DB is modeled indicate which attribute
  is a valid PRIMARY KEY for Table CUSTOMERS and
  which attribute is a FOREIGN KEY in Table DVD
  

18
Exercise (complex)
CUSTOMERS
DVD
19
Exercise (complex)
CUSTOMERS
DVD