DBMS Lecture 9  Object Database Management Group –12 Rules for an OODBMS –Components of the ODMG standard  OODBMS Object Model Schema  OO Data Model Design Notation  Oracle implementation of: –Inheritance –Aggregation

Rules that make it an OO system  Complex objects must be supported - objects whose data type is more than simply the native data types of number, string, date  Object identity – all objects must have a unique identity that is independent of the values of its attributes i.e. objects are not identified by primary key values

Rules that make it an OO system  Encapsulation must be supported i.e. access to an object is via its interface [cannot see the internal structure of an object or how its methods work]  Object classes the construct of object classes must be supported; the OODBMS schema must comprise a set of classes

Rules that make it an OO system  Inheritance of methods and attributes must be supported  Dynamic binding the DBMS must bind method names to logic at run time [allows for methods to have the same name but apply to different objects and implement in different ways]

Rules that make it an OO system  Complete DML should be a general purpose programming language  Extensible set of data types: the user must be able to build new data types from predefined types

Rules that make it an OO system  Recovery facilities must be able to recover from hardware and software failure  Query management must provide a simple way of querying the data

Rules that make it a DBMS In an OODBMS  Data persistence: data must persist after the application has terminated and the user should not need to explicitly initiate persistence.  Capable of managing very large databases  Concurrent access must be possible

Components of the ODMG [object database management group] standard 1Object Model: a data model to be supported by ODMG compliant DBMS 2Object specification language:  Object Definition Language [ODL] ODL used to define objects  Object Interchange Format [OIF] OIF used to upload and download object values to secondary storage

Components of the ODMG [object database management group] standard 3Object Query Language: a declarative language for querying the database - based on SQL3 4Language bindings ability to read and write from a database using different programming languages

Features of OODBM models  OODBM models real world entities as objects  Each object is composed of attributes and a set of methods  Each attribute can reference another object or set of objects  The attributes and the methods’ implementation are hidden, encapsulated from other objects

Features of OODM models  Each object is identified by a unique object id (OID) which is independent of the values of its attributes  Similar objects are grouped in a class that contains a description of the attributes and methods  The class describes a type of object

Features of OODM models  Classes are organized in a class hierarchy  Each object in a class inherits all properties of its superclasses in the class hierarchy

Comparing the OO and ER model Components  OO data model  Type  Object  Class  Instance variable  n/a  oid  method  class hierarchy  ER data model  entity definition  entity  entity set  attribute  primary key  n/a  ER diagram

Object Model: Objects  An object – instance of a class –has a unique identity –Property values –may have associated methods  Objects are defined against a type hierarchy: –Atomic [e.g. number, string, date] –Collection objects[ e.g. a set of students in a school]

Object Model: Types  Class definition defines the abstract behaviour and abstract state of an object type  A type has a specification –operations that can be performed –and properties that can be accessed  ODMG model includes supertyping and subtyping and the associated notion of inheritance or a generalisation – specialisation relationship

Object Model: Properties  Properties may either be an attribute of an object or a relationship between objects.  E.G. definition of attributes of a class: Module Attribute string moduleCode; Attribute string moduleName; Attribute short level; Attribute short roll;

Object Model: Properties - relationships  E.G. Lecturer teaches Module, Module is taught by Lecturer are the 2 traversal paths for the relationship teaches.  E.G. A one to many relationship between a Lecturer type and Module type: CLASS Lecturer { RELATIONSHIP SET Teaches INVERSE Module::TaughtBy; } CLASS Module { RELATIONSHIP Lecturer TaughtBy INVERSE Lecturer::Teaches; }

Object Model: Operations  the behaviour of an object is defined by a set of operations [methods] associated with an object.  E.G. An operation to increase the roll of a module instance by a set amount VOID increaseRoll (IN SHORT amount);

Object Model: schemas  Schemas : –database is defined by a schema specified in the object definition language.  schema information defined using ODL is stored in the system catalogue

Example Object Model Schema for an academic Database

OO Data Model Design Notation: Binary Relationships

OO Data model Design Notation: Inheritance

OO Data Model Design Notation: Aggregation

OO Data Model Design Notation: Reference

Implementing Inheritance in Oracle NOT INSTANTIATED

Storing Objects in tables  Either a super type table or series of sub type tables CREATE TABLE persons OF person_typ (CONSTRAINT persons_pk PRIMARY KEY (id));

Inserting data INSERT INTO persons VALUES(NEW employee1_typ(001, ‘bloggs’,’12-jun-2006’,12000,3000)); INSERT INTO persons VALUES(NEW student1_typ(001, ‘jones’,’12- jul-2006’,65));

Retrieving objects from object tables: SELECT VALUE (p) FROM persons p;

Example: Implementing Aggregation & Referencing in Oracle

Implementing Aggregation & Referencing in Oracle

workshop  Implementing an OO data model using SQL3 OO extension –Creating Object types –Creating tables for object types –Inserting data –Retrieving data