Object Oriented Databases

1
Object Oriented Databases

• Bringing objects into databases

2
An object database schema
ADDRESS Street String
City String PERSON
SS String Name String Address Address EMPL
OYEE ISA PERSON
Salary Integer Boss Employee Departments De
partment

• COMPANY
• Name String
• Head quarters Address
• Departments Department
• CEO Employee
• DEPARTMENT
• Name String
• Office Address
• Boss Employee
• Employees Employee

3
An object database query

• SELECT e.Name
• FROM e in EMPLOYEE, f in FILIAL
• WHERE e in f.Employees
• AND e.Address.City f.Office.City

4
Object database concepts
Person
Car
ssString,ageInteger
Types
Classes
lt11, 25,7gt
Objects
25,7 a1,b2
Complex values
11
bo
Simple values
25
5
Simple and complex values

• A is the set of all attributes
• O is the set of all object identifiers
• D is the union of integers, reals, strings, and
  booleans
• Elements in O U D are called simple values
• Elements of the form A1w1, , Anwn are tuple
  valueswhere Ai is an attribute and wi a value
• Elements of the form w1, , wn are set values
• A complex value is a tuple value or a set value

6
Objects

• An object is a pair
• (o, w)
• o is an object identifier
• w is a value

7
Examples of objects

• A SS, Name, Address, Main office, Filials,
  CEO
• O 11, 12, 13, 14, 21, 31, 41
• (11, SS 420101-1100, Name Bo Ek,
  Address Street Storg. 4, Town
  Karlstad)
• (14,Name Acme,Head office Street
  Storg. 12, Town Karlstad,Filials 21,
  31, 41,CEO 11)

8
Value and object equality

• Value equalityTwo objects are equal if their
  values are equal(o1, w1) (o2, w2) iff w1 w2
• Object equalityTwo objects are equal if their
  object identifiers are the same(o1, w1) (o2,
  w2) iff o1 o2

9
Surface and deep equality

• Surface equality equality without substituting
  object references
• Deep equality equality after substituting object
  references by values
• w1 A o1
• w2 A o2
• (o1, w)
• (o2, w)
• where o1 ? o2

w1 not surface equal to w2 w1 deep equal to w2
10
Surface and deep equality

• w1 A o1, B 25
• w2 A o2, B o3
• w3 A o2, B o4
• (o1, 25)
• (o2, 50)
• (o3, 25)
• (o4, o1)
• w1 deep equal to w2 ? w1 deep equal to w3?
  w2 deep equal to w3?

11
Types and classes

• Intuitions
• Values with the same structure are described by a
  type
• Object identifiers for similar objects are
  grouped into a class
• A class can be associated with a type to specify
  the structure of the objects of the class
• A class can be used as a type for typing
  references between objects

12
Types

• Let K be a set of classes.
• Base types integer, float, string, boolean
• Reference types K
• Tuple types elements of the formA1T1, ,
  AnTn, where Ai is an attribute and Ti en
  typa type
• Set types T, where T is a type
• A complex type is a tuple type or a set type

13
An example type

• K Car, Company, City
• EMPLOYEE
• SS Integer
• Name String
• Lives in City
• Works at Company
• Owns Car

Tuple type
Base type
Reference type
Set type
14
Object database schema

• An object database schema consists of
• A set of class names K
• For each k in K, a type that specifies the
  structure of k

15
Object database extension

• Given an object database schema S, an extension
  for S associates each k in K with a set of object
  identifiers

16
An example extension
1
2
3
4
K
5
Animal
Bird
4
5
Mammal
1
2
Dog
3
1
2
17
Types, classes, objects,and values
Pnr String, Namn String, Lön
Integer
K
Types
Person
Regnr String, Färg String, Ägare
Person
Bil
Pnr 5501010415, Namn Per
Svensson, Lön 25000
11
12
Regnr ABC123, Färg Röd, Ägare
11
21
O
22
W
18
Query languages
Viktiga egenskaper

• Allmängiltighet
• Deklarativitet
• Optimerbarhet
• Slutenhet
• Uttryckskraft
• Utvidgningsbarhet

19
Two simple queries

• SELECT a
• FROM a in EMPLOYEE
• WHERE Salary gt 20000

SELECT SS, Name FROM EMPLOYEE WHERE Salary gt
20000
20
Path expressions (dot notation)

• SELECT Name
• FROM Company
• WHERE Head_quarters.City London
• SELECT Name, Head_quarters.Street
• FROM Company
• WHERE Head_quarters.City London

21
Sets in queries

• What does this query mean?
• SELECT c
• FROM c in COMPANY
• WHERE CEO IN
• (SELECT e
• FROM e in EMPLOYEE
• WHERE Employee.Address.City Lund)

22
Sets in queries

• SELECT c.Name
• FROM c in COMPANY
• WHERE c.Departments.Office.City London, Lund

23
Sets and dot notation

• SELECT c.Departments.Employees.Salary
• FROM c in COMPANY
• c.Departments.Employees.Salary

f1, f2, f3
a1, a2 a3, a4 a5
100 200 150 100 150
f1, f2, f3
a1, a2, a3, a4, a5 ?
a1, a2, a3, a4, a5 ?
24
Sets and dot notation

• SELECT c.Departments.Employees.Salary
• FROM c in COMPANY

f1, f2, f3
a1, a2 a3, a4 a5
100 200 150 100 150
Answer 100, 150, 200
25
Exercises

• Which employees work at the same departments as
  their bosses?
• Which (pair of) employees work at the same
  departments?
• Which companies do not have any employee living
  in London?
• In which companies do all employees live in
  London?

26
Exercises

• Which employees work only at departments that are
  situated in London?
• Which employees do not work at a department in
  London?
• These queries become harder if the attribute
  Departments is removed. Try to write the
  queries also without this attribute.

27
Exercises

• In which companies are there employees who live
  in cities where the company does not have any
  department?
• In which companies does the boss of each employee
  live in the same city as the employee?

28

• Which employees work at the same departments as
  their bosses?

29

• Which (pair of) employees work at the same
  departments?

30

• Which companies do not have any employee living
  in London?

31

• In which companies do all employees live in
  London?

32

• Which employees work only at departments that are
  situated in London?

33

• Which employees do not work at a department in
  London?

34

• In which companies are there employees who live
  in cities where the company does not have any
  department?

35

• In which companies does the boss of each employee
  live in the same city as the employee?

36

• Which employees work at the same departments as
  their bosses?
• SELECT e.Name
• FROM e in EMPLOYEE
• WHERE e.Departments e.Boss.Departments

37

• Which (pair of) employees work at the same
  departments?
• SELECT e1.Name, e2.Name
• FROM e1 in EMPLOYEE, e2 in EMPLOYEE
• WHERE e1.Departments e2.Departments

38

• Which companies do not have any employee living
  in London?
• SELECT c
• FROM c in COMPANY
• WHERE London NOT IN c.Departments.Employees.Addr
  ess.City

39

• In which companies do all employees live in
  London?
• SELECT c
• FROM c in COMPANY
• WHERE c.Departments.Employees.Address.City
  London

40

• Which employees work only at departments that are
  situated in London?
• SELECT e.Name
• FROM e IN EMPLOYEE
• WHERE NOT EXISTS
• (SELECT d FROM DEPARTMENT
• WHERE e in d.Employees
• AND d.Office.City ltgt London)
• SELECT e.Name
• FROM e in EMPLOYEE
• WHERE e.Departments.Office.City London

41

• Which employees do not work at a department in
  London?
• SELECT e.Name
• FROM e in EMPLOYEE
• WHERE NOT EXISTS
• (SELECT d FROM d in DEPARTMENT
• WHERE e in d.Employees
• AND d.Office.City London)
• SELECT e.Name
• FROM e in EMPLOYEE
• WHERE London NOT IN e.Departments.Office.City

42

• In which companies are there employees who live
  in cities where the company does not have any
  department?
• SELECT c
• FROM c IN COMPANY
• WHERE c.Departments.Employees.Address.City MINUS
• c.Departments.Office.City ltgt Ø

43

• In which companies does the boss of each employee
  live in the same city as the employee?
• SELECT c
• FROM c in COMPANY
• WHERE NOT EXISTS
• (SELECT e
• FROM e in EMPLOYEE
• WHERE e IN c.Departments.Employees
• AND e.Boss.Address.City ltgt e.Address.City)

44

• Which employees work at a department in a city
  where they do not live?
• SELECT e.Name
• FROM e in EMPLOYEE, d in DEPARTMENT
• WHERE e in d.Employees
• AND d.Office.City ltgt e.Address.City

45

• Which employees live in the same city as (at
  least one of) their boss(es)?
• SELECT e.Name
• FROM e in EMPLOYEE, f in FILIAL
• WHERE e in f.Employees
• AND e.Address.City f.Boss.Address.City