Object Oriented Database By Ashish Kaul References from Professor Lee’s presentations and the Web.

As we have been discussing in class already, today I will be going over Object Oriented Database … To begin I will discuss why we would choose to use this style of a database over a relational database. Object Oriented Database

Relational databases store data in tables that are two dimensional. The tables have rows and columns. Relational database tables are "normalized" so data is not repeated more often than necessary. All table columns depend on a primary key (a unique value in the column) to identify the column. Once the specific column is identified, data from one or more rows associated with that column may be obtained or changed. Object Oriented Database vs. Relational Database

To put objects into relational databases, they must be described in terms of simple string, integer, or real number data. For instance in the case of an airplane. The wing may be placed in one table with rows and columns describing its dimensions and characteristics. The fuselage may be in another table, the propeller in another table, tires, and so on. Breaking complex information out into simple data takes time and is labor intensive. Code must be written to accomplish this task. Object Oriented Database vs. Relational Database cont…

Objects don't require assembly and disassembly saving coding time and execution time to assemble or disassemble objects. Reduced paging Easier navigation Better concurrency control - A hierarchy of objects may be locked. Data model is based on the real world. Works well for distributed architectures. Less code required when applications are object oriented. Object Oriented Database Advantages

Lower efficiency when data is simple and relationships are simple. Relational tables are simpler. Late binding may slow access speed. More user tools exist for RDBMS. Standards for RDBMS are more stable. Support for RDBMS is more certain and change is less likely to be required. Object Oriented Database Disadvantages

Object Identity (OID) Attributes (Instance variables) Object State Messages and Methods Encapsulated Structure –The ability to hide the object’s internal details Object Oriented Database Programming Terminology

Object Class –the logical structure of an object (name, attributes, methods) Object Class Library –a group of object classes Object –an instance of an object class Protocol – –collection of messages Object Oriented Database Programming Terminology cont…

Superclasses Subclasses Inheritance –Single –Multiple Polymorphism –situation in which one name can be used to invoke different functions Inheritance –automatically assuming the attributes and methods of another object at a higher class Object Oriented Database Programming Terminology cont…

System must support complex objects Object identifier must be supported Objects must be encapsulated Systems must support types or classes System must support inheritance System must avoid premature binding System must be computationally complete System must be extensible System must be able to remember data locations System must be able to handle very large databases System must support concurrent users System must be able to recover from hardware and software Data query must be simple 13 Rules for an OODBMS from the OODBS Manifesto

Medical care – X-rays, MRI, CT scans, and EKG traces Spatial and geographic databases – maps, seismic data, satellite images, CAD drawings Financial systems – time series data and analysis Where Object Oriented Databases are used

Impossible for a database vendor or a standards organization to incorporate all of these complex data types as an integral part of the RDBMS What we need is the capability to extend the set of built-in data types of the RDBMS A class encapsulating the data and methods of an ADT should satisfy the requirements How Object Oriented Databases are created

A new ADT would be implemented as a class in some object- oriented language The class would then be registered with the database system Once registered, the ADT becomes a candidate for an attribute type SQL extensions would allow the class methods to be used in queries How Object Oriented Databases are created cont…

The class is typically called a user-defined type (UDT) The class methods are called user-defined functions (UDF) Most implementations do not store instances of a class as part of a tuple Instead, a tuple contains a handle that refers to the instance of the UDT How Object Oriented Databases are created cont…

The data members of objects might be stored in one or more hidden tables Hidden indices can be implemented to accelerate access to the objects The object handle would also be used to access the UDFs of the class Some implementations allow the class designer to implement new access methods How Object Oriented Databases are created cont…

In these systems, a designer could simply use the index structures built into the DBMS – typically B + -trees For complex data, it may be faster to use a different structure Example – for searching spatial data, the R-tree (to be discussed later) would be a better choice How Object Oriented Databases are created cont…

A common use of UDTs is implement a container to hold multiple objects of the same (built-in or user-defined) type Such a type can be used to create a multivalued attribute Such a datatype does not violate first normal form, since the table does not contain repeating columns of the same type How Object Oriented Databases are created cont…

Object Oriented Database By Ashish Kaul THE END!!!!