Object relational database managmement systems (ORDBMS) Adapted by Edel Sherratt from originals by Nigel Hardy

ORDBMS Like a relational database management system But with classes and inheritance

Basic Idea Extend the relational model – do not throw away that strength – recognise that OO has additional strengths – add OO features to existing systems

Some examples Postgres – Illustra, acquired by Informix, in turn acquired by IBM – PostgreSQL Omniscience, Omniscience corporation, acquired by Oracle, became Oracle Lite DB2, Oracle database, Microsoft SQL Server

The Important extensions 1.structured types for attributes 2.references to tuples 3.methods 4.IDs for tuples but relations (and queries on them) remain central

Structured types for attributes As well as atomic types: int, float, char, boolean... Also allow structs, sets, bags, lists, arrays. And more complex arrangements: bags of structs i.e. relations

User defined types (UDTs) as attribute types CREATE TYPE addrType AS (street CHAR(50),city CHAR(20) ); CREATE TYPE student AS (name CHAR (30),sid char(9), address addrType ); CREATE TABLE company (name CHAR(20) PRIMARY KEY,address addrType ); keys are declared as part of tables - not UDTs

UDTs as table types CREATE TABLE students OF student; where student has three attributes 1.name 2.student_id 3.address and where address is a struct of – street – city

What about methods? include declaration in the type declare code separately CREATE TYPE student AS (... METHOD avgMark() RETURNS DECIMAL(5,2) ); CREATE METHOD avgMark() RETURNS DECIMAL(5,2) FOR student BEGIN... END;

What about Identity Often hidden from user But can be made visible can be SYSTEM GENERATED – like an OID can be DERIVED from the declared table key

And what about data manipulation? Essentially SQL, with programming language extensions Some extras – for example to enable access to object identifiers

Inheritance UDTs can “extend” UDTs – all the attributes and methods of the parent – plus any that are added tables can “extend” tables – all the attributes, keys and constraints of the parent – plus any that are added Keywords vary

Querying inheritance structures by default, querying a parent searches all subtypes the ONLY keyword limits it to the given table assume Staff is UNDER Person SELECT p.name FROM Person p; SELECT p.name FROM ONLY(Person) p; SELECT s.name FROM Staff s;

BLOBs and CLOBs Large OBjects Binary and Character stored and retrieved cannot take part in standard search comparisons – though CLOB can be searched for substrings CLOBs for texts, code BLOBs for images, sounds, video

ORDBMS - conclusion here and growing builds on RDBMS expertise using other widely available expertise introduces complexity and cost it does let us handle some of the difficult applications much more easily – but how common are they – must the “traditional” applications pay the cost?