Object-Oriented Database Management Systems (ODBMS) By Wendy Wooters CS157B

ODBMS Outline Definition Persistent Programming Languages Why Who Approaches Persistent Programming Languages Object-Oriented Concepts Object Class & Encapsulation Inheritance & Polymorphism Object Identifier (OID) Advantages and Disadvantages Example Code Conclusion

What is an ODBMS? Database that stores data elements as objects. Uses object-oriented concepts. Object - like an entity in and E-R Diagram. Employee Name Salary Hired SSN

Why use ODBMS? Complex data or relationship requirements Product DB Complex data or relationship requirements Lack of unique, natural identification Large numbers of many to many relationships Access using traversals. Graph/Tree structure. Frequent use of type codes such as those found in the relational schema Source: http://www.service-architecture.com/object-oriented-databases

Who Uses ODBMS? Typical Applications for ODBMS: Computer-aided design (CAD) Computer-aided software engineering (CASE) Multimedia databases Images, video, games, etc. Office automation systems (OIS) Expert database systems

Approaches for ODBMS Relational DB extended to use object-oriented concepts. (Object-relational DB) DB is Relational Programming language is object-oriented. RDB Application Translation Object-oriented DB model. Application and database use same object-oriented model. Uses persistent programming languages. ODB Application

Persistence Programming Languages A programming language that directly manipulates persistent data in a database. Persistent data exists after the program terminates. Single program for application and data management. No translation from database to application programming needed. Used with the object-oriented DB model approach. ODB Application

Object-Oriented Concepts Object Object is an entity containing: Variables/Attributes – Object Data Relationships – References to other objects Methods – Object Functions Messages – Accessing Methods Variables Methods Employee SSN:int Name:String Hired:Date Salary:double … getSSN() getName() setName() Relationships

Object-Oriented Concepts Class & Encapsulation Public class Employee { //Class Attributes private int SSN; private String name; private Date hired; private double salary; … //Class Constructor public Employee() {…} //Class Accessor Methods public int getSSN() {…} public String getName() {…} public Date getHired() {…} public double getSalary() {…} //Class Mutator Methods public void setName(String newName) {…} public void setHired(Date newHired) {…} public void setSalary(double newSalary) {…} } Class encapsulates the data structure and operations of the object. Internals are hidden from the user. User only knows available methods and how to call them.

Object-Oriented Concepts Inheritance & Polymorphism Inheritance - A class (subclass) can inherit the characteristic of another class (superclass). Example: Employee has inherited attributes and methods from Person. Polymorphism - Each subclass object can respond differently to same message by overriding the superclass method. Example: Person Employee Supplier Customer Subclass Superclass

Object-Oriented Concepts Object Identifier Object Identifier (OID) – The unique OID is maintained by the DBMS. ODBMS - Generated automatically by the system. Example: Reference to Date object in the Employee object for the date hired. RDBMS – Primary key. Example: SSN for Employee Date Employee

ODBMS Advantages Matches the object-oriented application design: Reduces code, execution time and paging Real world data model Easier Navigation Allows reusability of objects – generic objects can be used in many applications. Manages Complex data types more efficiently. Supports distributions of data across networks more efficiently.

ODBMS Disadvantages Still developing Lack of accepted standards Lack of development tools. Change is more likely to occur in model More complicated than the relational model. Takes longer to learn. Not as efficient when data and relations are simple.

Java & ODB Example import org.odmg.*; import java.util.Collection; Implementation impl = new com.vendor.odmg.Implementation(); Database db = impl.newDatabase(); Transaction txn = impl.newTransaction(); try { db.open("addressDB", Database.OPEN_READ_WRITE); txn.begin(); // perform query OQLQuery query = new OQLQuery( "select x from Person x where x.name = \“S. M. Lee\""); Collection result = (Collection) query.execute(); Iterator iter = result.iterator(); // iterate over the results while ( iter.hasNext() ) { Person person = (Person) iter.next(); // do some addition processing on the person (now shown) // now traverse to the address object and update its value person.address.street = "13504 4th Avenue South"; } txn.commit(); db.close(); //exception handling would go here ... Example of how to access data in an ODB, using the ODMG Object Query Language (OQL): Opens DB Starts a transaction Executes a query to find a Person object named “S. M. Lee” Does additional processing on this Person object Gets Address object of Person Update street of Address object Commit transaction Close database Source: http://www.service-architecture.com/object-oriented-databases

Conclusion Definition Persistent Programming Languages Object-Oriented Concepts Advantages and Disadvantages of ODBMS Example Code