Lecture 33: Object-Oriented Databases

CSCI403Lecture 33: Object-Oriented Databases

Goal: SimpleProgrammaticPersistence &Retrieval

Using an RDBMS• Save object attributes to tables• Manually• Using an ORM• Challenge: object data must “become” arecord and vice-versa

Object-OrientedDatabase SystemsWhy not store objects as objects?

http://tinyurl.com/3zjndzc

What’s an OODB?• It should be a DBMS• Persistence• Storage management• Concurrency• Recovery• Ad hoc query support

What’s an OODB?• Consistent w/ modern OO paradigms• Complex objects• Object identity• Encapsulation• Types (classes)• Inheritance• Overriding• Extensibility• Computational completeness

HighlightsAn RDBMS only persists object state.age, nameAn OODB persists state & behavior.age, name, dance(), drink()

HighlightsAn RDBMS manages identificationprimary keys... what does “identity” mean in the OO model?

Who’s Your Daddy?(Object Identity vs. Object Equality)Person{ name: Jack,age: 40,son: Person { name: John, age:15}}Person{ name: Diane,age: 32,son: Person { name: John, age:15}}

OODBs & Identity• Identity is achieved through a graph• Transparent• Works great for a single application session• Identity is achieved through ID generation• Managed internally by the OODB• Roughly similar to primary keys

Why an OODB?• Composite objects & relationships• Preserves class hierarchy (no STI)• No formal query language necessary• No “impedance mismatch”• One data model

Why Not?• Sensitive to schema changes• Language / API dependent• Limited ad-hoc queries(All of these issues have evolved and aredependent on the OODB being used)

Example

Homework• Read “An Exploration of Object OrientedDatabase Management Systems” (Obasanjo)• Read “The Object-Oriented Database SystemManifesto” (Atkinson et al)• http://developer.db4o.com/Documentation.aspx