Advanced Database Systems

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Object-Oriented Databases
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Weaknesses of Relational DBMSs

• Poor representation of 'real world' entities
• Poor support for integrity and business rules
• Homogenous data structure
• Limited operations
• Difficulty handling recursive queries
• Impedance mismatch

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Object-Oriented Concepts

• Abstraction
• Encapsulation
• Information hiding
• Object
• Contains both attributes and associated functions
  (methods)
• Object Identity (OID)
• Methods and Messages
• Class
• Subclass, Superclass

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. . . Object-Oriented Concepts

• Inheritance
• Single, Multiple, Selective
• Overriding
• Overloading
• Polymorphism
• Operation Polymorphism (Overloading)
• Inclusion Polymorphism
• Parametric Polymorphism
• Dynamic (late) Binding
• Complex Objects

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Object-Oriented Databases

• Relational data model is quite successful in
  modeling traditional business database
  applications
• New emerging complex applications such as
  CAD/CAM, scientific databases, GIS, and
  multimedia databases have new requirements
• Object-oriented database were proposed to meet
  the needs of these more complex applications
• Object-oriented (OO) technology has its origin in
  OO in programming languages (SIMULA, SMALLTALK,
  C, Java)
• OO languages create transient objects, where OO
  databases create persistent and sharable objects

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OODBMS Overview

• Every object is identified by an object
  identifier ( OID )
• Attributes of objects can themselves be objects.
  This allows for complex nesting of objects.
• OODBMS allow behaviors that operate on data,
  which is similar to the Object-oriented languages.

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OODBMS Overview

• OODMS have inheritance which permits new types
  that inherit structure from parent types.
• OODMS support operator overloading where a single
  operator can have multiple implementations
  depending on the type of data that it operates on.

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Object Identity

• OODMS generate unique immutable OID value for
  each object, which is invisible to the user.
• When nesting objects, the OID is used as a
  pointer to reference children objects.

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Type Constructors

• Type constructors allow the construction of a
  complex object by specifying a triple
• i unique object id
• c type constructor
• v value

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Type Constructors
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Example
define type Department tuple ( dname string
dnumber integer mgr tuple
(manager Employee
startdate Date ) locations
set(string) employees set(Employee)
projects set(Project) )
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Operations on Data

• Objects have two components
• State structure of data
• Behavior determined by methods
• External users of objects only know about the
  interface, not implementation.
• Allows for information hiding and data
  encapsulation.

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Example
define class Department type tuple ( dname
string dnumber integer
mgr tuple (manager Employee
startdate Date )
locations set(string)
employees set(Employee)
projects set(Project) ) operations (
no_of_emps integer create_dept
Department desroy_dept boolean
assign_emp(e Employee) boolean
remove_emp(e Employee) boolean
) end Department
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Object Definition Language

• A user can specify object database schema

class Faculty extends Person ( extent faculty )
attribute string rank attribute float
salary attribute string office attribute
string phone relationship Department
works_in inverse Departmenthas_faculty
relationship set ltGradStudentgt advises
inverse Gradstudentadvisor
relationship set ltGradStudentgt on_committee_of
inverse
Gradstudentcommittee void give_raise ( in
float raise ) void promote( in string new_rank
)
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Object Query Language

• select struct (name struct (last_name
  s.name.lname,
• first_name
  s.name.fname),
• degrees(select struct (deg
  d.degree,
• yr d.year,
• college
  d.college)
• from d in s.degrees)
• from s in csdepartment.chair.advises

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Encapsulation

• Interface (signature) define operations
• Implementation (method)
• A method is invoked by sending a message
• Dot notation
• We can divide the structure of an object into
  visible and hidden attributes
• Class an object type definition
• Persistent object by naming and reachability

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Example
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Type Hierarchies

• OO databases permit the definition of new types
  (extensible type systems)
• Type name functions (attributes and
  operations)
• PERSON Name, Address, Birthdate, Age
• Subtype inherits all the functions of the
  supertype
• EMPLOYEE subtype-of PERSON Salary, Hiredate
• STUDENT subtype-of PERSON Major, GPA
• Renaming of inherited functions
• Type hierarchy

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Class Hierarchies

• A class is a collection of objects that are
  meaningful to some applications
• Subclass and superclass
• Predefined system class
• An object value may be a class (a collection of
  other objects)
• It is possible to create a default class for each
  type to hold persistent objects of that type
• Persistent class and transient class

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Complex Objects

• Unstructured
• permits storage and retrieval of large objects,
  such as images, long text strings, video, images
• Also known as binary large objects (BLOBs)
• Structured
• structure of object is known to database
• defined by type constructors such as set, tuple,
  bag, array, list

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Complex Objects

• Unstructured complex object
• Binary large objects (BOLBs)
• For example 2D bitmap images
• RDBMS
• OODBMS
• A new type that define structure and operations
• Structured complex objects
• Department
• Ownership semantics encapsulated objects
• Reference semantics referenced objects

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Other Concepts

• Polymorphism operator overloading
• Multiple inheritance
• Type lattice
• Selective inheritance
• Versions

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Object-Relational DBMSs

• Tables with methods
• Nested tables
• Object views
• Determine the query the view will represent
• Determine the datatypes the query will return
• Create a type that has the same structure as the
  query
• Crete the view based on the type
• Large objects
• BLOB (binary large objects)
• CLOB (character large object)
• BFILE (binary files stored outside the database)

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Object-Relational Features of Oracle 8

• Multivalued Attributes Using VARRAY
• CREATE TYPE phone_num_type AS OBJECT(phone_number
  CHAR(10))
• CREATE TYPE phone_list_type AS VARRAY(5) OF
  phone_num_type
• Nested Tables to Represent Complex Objects
• Object Views

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Object-Relational Support in SQL3

• Objects in SQL3
• Tuple type
• CREATE ROW TYPE emp_row_type ( )
• CREATE ROW TYPE comp_row_type ( )
• CREATE ROW TYPE employment_row_type ( employee
  REF (emp_row_type), company REF
  (comp_row_type))
• CREATE TABLE employment OF TYPE
  employment_row_type
• Abstract Data Types (ADT)
• CREAT TYPE type_name ( list of component
  attributes with individual types declaration of
  functions (methods))
• Inheritance
• CREATE TABLE graduate_student UNDER student

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The Nested Relational Data Model

• Non-1NF
• dept (dno, manager, employees, projects,
  locations)employees (ename, dependents)project
  s (pname, ploc)locations (dloc)dependents
  (dname, age)
• SQL3 nest and unnest functions

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Conclusion

• Object-oriented databases allows for data
  abstraction, information hiding, and inheritance.
  
• Allows storage of both structured and
  unstructured complex objects.
• OODMS provide a useful alternative to relational
  databases when dealing with data such as bitmap
  images, audio, or video.