Object relational database managmement systems (ORDBMS)

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

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

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

4. 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

5. The Important extensions • structured types for attributes • references to tuples • methods • IDs for tuples • but relations (and queries on them) remain central

6. 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

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

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

9. 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;

10. 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

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

12. 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

13. 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;

14. 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

15. 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?