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Understanding Object-Relational Database Management Systems (ORDBMS): Features and Implications

This overview explores Object-Relational Database Management Systems (ORDBMS), diving into their necessity and advantages. It discusses the limitations of traditional relational databases (RDBMS) in handling advanced applications and how ORDBMS addresses these through Object-Oriented (OO) features such as user-extensible types, encapsulation, inheritance, and polymorphism. The chapter also weighs the pros and cons, like increased complexity and costs, and outlines new SQL features introduced in SQL:2003 that enhance functionality. Overall, the text highlights ORDBMS's potential to bridge the gap between traditional RDBMS and modern database needs.

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Understanding Object-Relational Database Management Systems (ORDBMS): Features and Implications

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Presentation Transcript

  1. Chapter 2 Object-Relational DBMSs Chapter 28 in Textbook

  2. Overview • Why ORDBMS? • What is ORDBMS? • Stonebreaker’s view • Advantages and disadvantages of ORDBMS • New OO features in SQL

  3. Why ORDBMS – Extending RDBMS • Vendors of RDBMSs conscious of threat and promise of OODBMS. • Agree that RDBMSs not currently suited to advanced database applications, and added functionality is required. • Reject claim that extended RDBMSs will not provide sufficient functionality or will be too slow to cope adequately with new complexity. • Can remedy shortcomings of relational model by extending model with OO features.

  4. What is ORDBMS? • ORDBMS is a relational database with OO features. • OO features being added include: • User-extensible types. • Encapsulation. • Inheritance. • Polymorphism. • Dynamic binding of methods. • Complex objects. • Object identity.

  5. Stonebraker’s View

  6. Advantages of ORDBMSs • Resolves many of known weaknesses of RDBMS. • Reuse and sharing: • reuse comes from ability to extend server to perform standard functionality centrally; • Preserves significant body of knowledge and experience gone into developing relational applications.

  7. Disadvantages of ORDBMSs • Complexity. • Increased costs. • Proponents of relational approach believe simplicity and purity of relational model are lost. • Some believe RDBMS is being extended for what will be a minority of applications. • OO purists not attracted by extensions either. • SQL now extremely complex.

  8. SQL:2003 - New OO Features • Type constructors for row types and reference types. • User-defined types (distinct types and structured types) that can participate in supertype/subtype relationships. • User-defined procedures, functions, methods, and operators. • Type constructors for collection types (arrays, sets, lists, and multisets). • Support for large objects – BLOBs and CLOBs. • Recursion.

  9. Subtables and Supertables • No mechanism to store all instances of given UDT, unless user explicitly creates a single table in which all instances are stored. • Thus, in SQL:2003 may not be possible to apply an SQL query to all instances of a given UDT. • Can use table inheritance, which allows table to be created that inherits all the rows of one or more existing tables. • Subtable/supertable independent from UDT inheritance facility. • Subtable/supertable: rows are inherited. • Subtype/supertype: attributes and methods are inherited.

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