Chapter 17 - Object-Oriented Database Processing

A Sketch of Object-Oriented Programming
1. OOP Terminology
  - OOP object is an encapsulated structure(self contained) with attributes and methods(sequence of instructions)
  - interface - external appearance of an object
  - implementation - encapsulated internals of an object
  - inheritance - subclasses and superclasses
  - polymorphism - calling special versions of a method for different subclasses of the same class
  - object class - logical structure of an object (name, attributes, methods)
  - object - instance of an object class
  - transient object - only exists in volatile memory during execution of a program
  - persistent object - has been saved to permanent storage
OOP Example - see Fig. 17-3
Object Persistence
- save object instances data values
- convert in-memory object pointers to permanent, unique IDs (swizzling)
- save object class methods
1. Object Persistence Using Tradional File Storage lot of work for programmer; only works when application has a few simple objects whose structure does not change
2. Object Persistence Using Commercial Relational DBMS programmer needs to define relational structures to represent objects, write the code to interface with the DBMS to get / put obhects and to swizzle pointers
3. Object Persistence USing ODBMS - designed for object persistence [just save ODB]
Comparing ODBMS and Traditional DBMS
1. ODBMS Advantages
  - integrated with programming language
  - automatic method storage
  - user-defined types
  - complex data readily processed
  - automatic persistent object IDs
  - single-level memory
2. ODBMS Disadvantages
  - requires OOP
  - little existing data in object form
  - nonexistent (or poor) query and reporting tools
  - limited concurrency control and transaction management
  - unproven performance
  - substantial change and learning required
3. Are ODBMS Better than Traditional DBMS?
ODBMS Standards
1. SQL3
  Abstract data type(ADT) - user-defined structure that is equivalent to an OOP object
2. ODMG-93
  - Objects are fundamental
  - Every object has a lifelong persistent, unique identifier
  - Objects can be arranged into types and subtypes
  - State is defined by data values and relationships
  - Behaviour is defined by object operations