1. Object-oriented DBMSs
Chapter 1
Object-oriented DBMSs
Chapters in Textbook

2. Overview Relational quick review Why OO? What is an Object?
What is an object ID?
Classes, subclasses and inheritance
UML
ODL
OQL
OODBMS

3. Relational DBMS Quick Review
Data model: ER.
Data is stored in tables.
Each row is a record.
Relationships between tables (PK-FK).
Takes
SID
Student
Course
CID
name
year
Sem
name
SID
name
Nora M
Sara S
Hala L
SID
CID
year
Sem
CAP364
1425 1
CAP430
1426 2
CID
name
CAP364
DB2
CAP430
Security
OODBMS

4. Weaknesses of RDBMS Poor Representation of “Real World” Entities.
Poor Support for Integrity and Enterprise Constraints.
Homogeneous Data Structure.
Limited Operations.
Difficulty Handling Recursive Queries.
Schema changes are difficult.
RDBMSs are poor at navigational access.
OODBMS

5. Why OO? Advanced DB Applications
Computer-Aided Design (CAD).
Computer-Aided Manufacturing (CAM).
Computer-Aided Software Engineering (CASE).
Network Management Systems.
Office Information Systems (OIS) and Multimedia Systems.
Digital Publishing.
Geographic Information Systems (GIS).
Interactive and Dynamic Web sites.
Other applications with complex and interrelated objects and procedural data – Read pages in book.
OODBMS

6. What is an OODBMS anyway?
OODBMS (Object-oriented DB Management System) is a database with data stored in objects and collections NOT rows and tables.
OO Concepts:
Abstraction, encapsulation, information hiding.
Objects and attributes.
Object identity.
Methods and messages.
Classes, subclasses, superclasses, and inheritance.
Overloading.
Polymorphism and dynamic binding.
OODBMS

7. OODBMS OODBMS Traditional DBS Persistence Sharing Transactions
Concurrency Control
Recovery Control
Security
Integrity
Querying
Semantic Data Model
Generalization
Aggregation
OOPS
OID
Encapsulation
Inheritance
Types & Classes
Methods
Complex objects
Polymorphism
Extensibility
Special Requirements
Versioning
Schema Evolution
OODBMS
OODBMS

8. Object Uniquely identifiable entity that contains both
the attributes that describe the state of a real-world object
and
the actions associated with it.
Object encapsulates both state and behavior; an entity only models state.
Persistent objects vs. transient objects.
Everything in an OODBMS is an object.
OODBMS

9. Object Identity (OID)
Object identifier (OID) assigned to object when it is created that is:
System-generated.
Unique to that object.
Invariant.
Independent of the values of its attributes (that is, its state).
Invisible to the user (ideally).
OODBMS

10. OID Alternative 1
In RDBMS, object identity is value-based: primary key is used to provide uniqueness.
Why not use primary key in OODBMS?
Primary keys do not provide type of object identity required in OO systems:
key only unique within a relation, not across entire system;
key generally chosen from attributes of relation, making it dependent on object state (simulated key).
OODBMS

11. OID Alternative 2
In OO programming languages, use variable names and pointers/virtual memory addresses, which also compromise object identity.
In OOPL, OID is physical address in process memory space, which is
too small - scalability requires that OIDs be valid across storage volumes, possibly across different computers.
Further, when object is deleted, memory is reused, which may cause problems.
OODBMS

12. OID Advantages They are efficient. They are fast.
They cannot be modified by the user.
They are independent of content.
Identical objects vs. equal objects
OODBMS

13. Encapsulation Object Attributes Method 1 Method 2 Method 4 Method 3
OODBMS

14. Class and Object (Instance)
BranchNo = B005
Street = 22 Deer Rd
City = London
Postcode = SW1 4EH
BRANCH
Attributes
branchNo
street
city
postcode
BranchNo = B007
Street = 16 Argyll St
City = Aberdeen
Postcode = AB2 3SU
Methods
print()
getPostCode()
numberOfStaff()
BranchNo = B003
Street = 163 Main St
City = Glasgow
Postcode = G11 9QX
OODBMS

15. Subclasses, Superclasses and Inheritance
Inheritance allows one class of objects to be defined as a special case of a more general class.
Special cases are subclasses and more general cases are superclasses.
Process of forming a superclass is generalization; forming a subclass is specialization.
Subclass inherits all properties of its superclass and can define its own unique properties.
Subclass can redefine inherited methods (override).
All instances of subclass are also instances of superclass.
OODBMS

16. Single Inheritance
PERSON
STAFF
MANAGER
SALES
STAFF
OODBMS

17. Complex Objects
A Complex object is something that can be viewed as a single thing in the real world but it actually consists of many sub-objects.
2 Types:
Unstructured.
Their structure hard to determine.
Requires a large amount of storage.
BLOB (Binary Large Objects): images & long test strings.
Structured.
Clear structure.
Sub-objects in a part-of relationship.
Will talk more about in next slide.
OODBMS

18. Structured Complex Objects
An object that consists of sub-objects but is viewed as a single object.
Objects participate in a A-PART-OF (APO) relationship.
Contained object can be encapsulated within complex object, accessed by complex object’s methods.
Or have its own independent existence, and only an OID is stored in complex object. M1 M3 M2 M4
Obj 2
Obj 1 M1 M3 M2 M4
Obj 1
OID 2 M1 M3 M2 M4
Obj 3
OID 2
Obj 2
OODBMS

19. Commercial OODBMs GemStone from Gemstone Systems Inc.,
Itasca from Ibex Knowledge Systems SA,
Objectivity/DB from Objectivity Inc.,
ObjectStore from eXcelon Corp.,
Ontos from Ontos Inc.,
Poet from Poet Software Corp.,
Jasmine from Computer Associates/Fujitsu,
Versant from Versant Object Technology.
OODBMS

20. Components of OODBMS
Object Model (OM): abstract modeling of objects and relationships.
Unified Modeling Language (UML): used to describe OM.
Object Definition Language (ODL): language to specify the schema for an OODBMS.
Object Query Language (OQL): Language to query an OODBMS.
C++, Smalltalk, and Java Language Binding.
OODBMS

21. Object Model -- Collections
Contains a number of unnamed, homogeneous elements; each can be instance of atomic type, another collection, or a literal type.
Types of Constructors:
Set: unordered collection of objects without duplicates.
Bag: unordered collection of objects that allows duplicates.
List: ordered collection of objects that allows duplicates.
Array: ordered collection of objects without duplicates.
Dictionary: unordered sequence of key-value pairs without duplicate keys.
OODBMS

22. OM – Object Relationships
A relationship between 2 objects can be:
One-to-One
One-to-Many
Many-to-Many
UML (Unified Modeling Language) is used to model objects and object relationships.
OODBMS

23. UML Example PERSON STAFF POWNER CLIENT BRANCH MANAGER SALESTAFF
Name
FName
LName
STAFF
StaffNo
position
DOB
salary
POWNER
OwnerNo
address
CLIENT
ClientNo
telNO
prefType
MaxRent
MANAGER
SALESTAFF
BRANCH
PROPERTY
PropertyNo
rooms
rent
BranchNo
Manages
WorksAt
Offers
Views
Owns 1
OwnedBy N
ViewedBy M M M 1 M
Has 1 1 1
ManagedBy
IsOfferedBy
OODBMS

24. Object Definition Language -- ODL
module DreamHome
Class Branch
(extent branchOffices key branchNo) {
attribute string branchNo;
attribute struct BranchAddress {string street, string city, string postcode} address;
relationship Manager ManagedBy inverse Manager::Manages;
relationship set<SalesStaff> Has inverse SalesStaff:WorksAt;
relationship set<PropertyForRent> Offers inverse PropertyForRent::IsOfferedBy;
void takeOnPropertyForRent(in string propertyNo)
raises(propertyAlreadyForRent); };
OODBMS

25. ODL
class Person {
attribute struct Pname {string fName, string lName} name; };
Class Staff extends Person
(extent staff key staffNo) {
attribute staffNo;
attribute enum SexType {M, F} sex;;
attribute date DOB;
short getAge();
Void increaseSalary(in float increment);
class Manager extends Staff
(extent managers)
relationship Branch Manages inverse Branch::ManagedBy;
OODBMS

26. Object Query Language -- OQL
A Query language for OODBMS.
OQL can be used for both associative and navigational access:
Associative query returns collection of objects (like SQL).
Navigational query accesses individual objects and object relationships used to navigate from one object to another.
OODBMS

27. OQL
SELECT [DISTINCT] <expression> FROM <fromList> [WHERE <expression>] [GROUP BY <attribute1: expression1, attribute2, expression2, ..>] [HAVING <predicate>] [ORDER BY <expression>]
OODBMS

28. OQL vs. SQL: A Simple Example
Query:
List the names of the children of employees working in the sales department.
OQL
SQL
select c.fname, c.lname from Depts d, d.employs e, e.hasChildren c where d.name = “Sales”
select
c.fname, c.lname
from
Depts d, Employee e,
Children c
where
d.name = “Sales” and
d.deptID = e.deptID and
c.parentID = e.empID
OODBMS

29. OQL: Extents
Find all branches in London: SELECT b.branchNo FROM branchOffices b WHERE b.address.city = “London”; This returns a type bag<string> but since branchNo is unique  set<string>.
OODBMS

30. OQL: Traversal Paths
Find the salaries of sales staff who work at the branches in London SELECT DISTINCT s.salary FROM BranchOffices b, b.WorksAt s WHERE b.address.city = “London”; This returns set<float>.
OODBMS

31. OQL: Using Structures
Get structured set containing name, sex, and age for all staff who live in London: SELECT struct (lName:s.name.lName, sex:s.sex, age:s.getAge()) FROM s IN Staff WHERE s.WorksAt.address.city = “London”; This returns bag<struct>.
OODBMS

32. OQL: Order By
Get structured set containing name, sex, and age for all staff who live in London ordered by their salaries: SELECT struct (lName:s.name.lName, sex:s.sex, age:s.getAge()) FROM s IN Staff WHERE s.WorksAt.address.city = “London” ORDER BY s.salary; This returns a type list<struct>.
OODBMS

33. OQL: Aggregates
How many staff work in branch number 003? 2 ways to query
SELECT COUNT(s)
FROM s IN salesStaff
WHERE s.WorksAt.branchNo = “B003”;
COUNT(SELECT s FROM s IN salesStaff
WHERE s.WorksAt.branchNo = “B003”);
Return staff who work in branches with more than 10 employees
SELECT s
FROM s IN salesStaff
WHERE COUNT(s.WorksAt) > 10;
COUNT can be used in any part of the OQL
OODBMS

34. OQL: Creating Objects
A type name constructor is used to create an object with identity: Manager(staffNo: “SL21”, fName: “John”, lName: “White”, address: “19 Taylor St, London”, position: “Manager”, sex: “M”, DOB: date“ ”, salary: 30000)
OODBMS