Jane Reid, BSc/IT DB, QMUL, 25/2/02 1 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)

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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 3 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 4 Background to ODBMS [3] Advantages: –Ability to deal with complex objects –Improved performance Disadvantages: –Lack of standards –Lack of security

Jane Reid, BSc/IT DB, QMUL, 25/2/02 5 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 6 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 7 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)

Jane Reid, BSc/IT DB, QMUL, 25/2/02 8 Object components [2] Object identifier (OID) –Logical –Physical

Jane Reid, BSc/IT DB, QMUL, 25/2/02 9 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 10 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 11 Graphical ODB schema [2] Notation (subset only) Class Relationships1:1 1:N M:N Class inheritance Student

Jane Reid, BSc/IT DB, QMUL, 25/2/02 12 Graphical ODB schema: ex [1] Person NameAddress DriverPassenger d Staff# SeasonTicket RouteInstance Date ArrTime DepTime Bus Route drives runs instance of travels Route# From To M N 1 N M N 1 N Reg# Capacity

Jane Reid, BSc/IT DB, QMUL, 25/2/02 13 Graphical ODB schema: ex [2] Person DriverPassenger BusRoute RouteInstance drives is driven by runs on served by travels on run for has instance instance of

Jane Reid, BSc/IT DB, QMUL, 25/2/02 14 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 15 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 16 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 1:1 / 1:N relationship - reference attributes single-valued M:N relationship - reference attributes set-valued or list-valued

Jane Reid, BSc/IT DB, QMUL, 25/2/02 17 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 18 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 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 19 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)

Jane Reid, BSc/IT DB, QMUL, 25/2/02 20 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)

Jane Reid, BSc/IT DB, QMUL, 25/2/02 21 ODB schema: ex [3] Class RouteInstance Attributes: Date, ArrTime, DepTime, Bus (reference), Route (reference) Operations: getPassengerNumbers, calculateUsage

Jane Reid, BSc/IT DB, QMUL, 25/2/02 22 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

Jane Reid, BSc/IT DB, QMUL, 25/2/02 23 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