Object-oriented%20DBMS

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Object-oriented DBMS

• Background to ODBMS
• ODBMS requirements
• Object components
• ODB conceptual design
• Graphical ODB schema
• ODB schema definition (using ODL)
• Object-relational DBMSs (ORDBMS)

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Background to ODBMS 1

• Based on concepts and principles of OO
  programming languages
• Motivations
• Direct integration with OO PLs
• Easier implementation of multimedia systems
• Matches application domain more closely
• Encourages modular design
• Promotes use of reusable and extensible
  components

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Background to ODBMS 2

• OMG consortium produced ODMG 3.0 standard (1999)
• Object model
• Object definition language (ODL)
• Object query language (OQL)
• Bindings to OO programming languages

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Background to ODBMS 3

• Advantages
• Ability to deal with complex objects
• Improved performance
• Disadvantages
• Lack of standards
• Lack of security

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ODBMS requirements 1

• From OO domain
• Support for complex objects (set, tuple, list)
• Support for object identity
• Support for encapsulation
• Support for classes
• Support for inheritance (possibly multiple,
  selective)
• Dynamic binding (to allow overloading and
  overriding)
• DML must be computationally complete (i.e. a
  general-purpose PL)
• Set of data types must be extensible

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ODBMS requirements 2

• From DBMS domain
• Data persistence
• Ability to manage VLDBs
• Support for concurrent users
• Ability to recover from hardware / software
  failure
• Facility for querying in a high-level, efficient,
  application-independent way

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Object components 1

• State (value), constructed by type constructor
• Atomic type
• Structured type tuple
• Collection types
• set (unordered, no duplicates)
• list (ordered, duplicates)
• References (including inverse references)
• Behaviour (operations)
• Signature (interface)
• Method (body)

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Object components 2

• Object identifier (OID)
• Logical
• Physical

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ODB conceptual design

• ODB / RDB conceptual design differences
• Relationships
• ODB - OID references
• RDB - value references in foreign keys
• Inheritance
• ODB - inheritance constructs
• RDB - no built-in constructs
• Operation specification
• ODB - in class specification
• RDB - at implementation stage

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Graphical ODB schema 1

• Can be mapped from EER schema but
• Cannot (directly) model
• Categories (union types)
• Ternary or higher degree relationships
• Relationship attributes
• Can model interface inheritance

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Graphical ODB schema 2

• Notation (subset only)
• Class
• Relationships 11
• 1N
• MN
• Class inheritance

Student
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Graphical ODB schema ex 1

Name
Address
Person
d
Staff
SeasonTicket
Driver
Passenger
M
M
Reg
Route
drives
travels
N
N
Bus
Route
1
runs
instance of
1
From
Capacity
To
N
N
ArrTime
Date
RouteInstance
DepTime
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Graphical ODB schema ex 2
Person

Driver
Passenger
drives
travels on
is driven by
run for
Bus
Route
runs on
has instance
served by
instance of
RouteInstance
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ODB schema definition

• Uses ODL
• PL-independent
• Specific PL bindings used at implementation
• Produced from
• EER schema and/or graphical ODB schema
• Added class operations

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Creating an ODB schema 1

• Stage 1 - create ODL class for each entity type /
  subclass
• Include attributes of EER class
• Multi-valued attributes declared with set or list
  constructors
• Composite attributes declared with tuple
  constructor
• Declare an extent for each class
• Key attributes are keys of the extent

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Creating an ODB schema 2

• Stage 2 - add reference attributes for each
  binary relationship
• Attributes added into participating ODL classes
• May be created in one or both directions
• One direction - attribute in referencing class
• Both directions - inverse
• Cardinality ratio
• 11 / 1N relationship - reference attributes
  single-valued
• MN relationship - reference attributes
  set-valued or list-valued

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Creating an ODB schema 3

• Stage 3 - include class operations
• Constructor method checks creation constraints
• Destructor method checks deletion constraints
• Stage 4 - ODL classes formed from EER subclasses
• Inherits type and methods of ODL superclass
• Define specific attributes, relationship
  references and operations

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Creating an ODB schema 4

• Problem issues
• Weak entity types can be defined
• In same way as strong entity types
• As composite, multi-valued attributes of owner
  entity type
• Categories may be represented by
• Declaring class and defining 11 relationship
  with each superclass
• Using union type (if available)
• Ternary / higher degree relationships may be
  mapped
• Into a separate class with references to
  participating classes
• By 1N relationship from participating classes to
  class that represents the higher degree
  relationship

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ODB schema ex 1

• Class Person
• Attributes Name (key), Address
• Class Driver (inherits from Person)
• Attributes Staff (key), set of Bus (reference)
• Class Passenger (inherits from Person)
• Attributes SeasonTicket (key), set of Route
  (reference)

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ODB schema ex 2

• Class Bus
• Attributes Reg (key), Capacity, set of
  RouteInstance (reference), set of Driver
  (reference)
• Operations getCapacity
• Class Route
• Attributes Route (key), To, From, set of
  RouteInstance (reference), set of Passenger
  (reference)

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ODB schema ex 3

• Class RouteInstance
• Attributes Date, ArrTime, DepTime, Bus
  (reference), Route (reference)
• Operations getPassengerNumbers, calculateUsage

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ORDBMS 1

• Aka extended relational DBMS
• Enhance RDBMS with some OO features
• Oracle ORDBMS features
• User-defined data types
• Object types
• Collection types
• (Limited) support for multimedia data types
• Methods
• OIDs
• REF data type
• (Virtual) object views

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ORDBMS 2

• ORDBMS make use of OO features of SQL3
• New data types
• Boolean
• Character
• LOB
• Object types and built-in object functions
• Inheritance
• Collection type constructors
• Overloading