Jane Reid, BSc/IT DB, QMUL, 25/2/02 1 Object-oriented DBMS Background to ODBMS ODBMS requirements...

Jane Reid, BSc/IT DB, QMUL, 25/2/02

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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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• 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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• 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 1:1

1:N

M:N

Class inheritance

Student


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Graphical ODB schema: ex [1]

PersonName Address

Driver PassengerdStaff# SeasonTicket

RouteInstanceDate ArrTime

DepTime

Bus Route

drives

runs instance of

travelsRoute#

FromTo

M

N

1N

M

N1

N

Reg#

Capacity


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Graphical ODB schema: ex [2]

Person

Driver Passenger

Bus Route

RouteInstance

drives

is driven by

runs on

served by

travels on

run for

has instance

instance of


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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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• 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• 1:1 / 1:N relationship - reference attributes single-valued

• M:N relationship - reference attributes set-valued or list-valued


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• 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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• 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 1:1 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 1:N relationship from participating classes to class that represents the higher degree relationship


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ODB schema: ex [1]

Class PersonAttributes: 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 BusAttributes: Reg# (key), Capacity, set of RouteInstance (reference), set of Driver (reference)

Operations: getCapacity

Class RouteAttributes: Route# (key), To, From, set of RouteInstance (reference), set of Passenger (reference)


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ODB schema: ex [3]

Class RouteInstanceAttributes: 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 1 Object-oriented DBMS Background to ODBMS ODBMS requirements...

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