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Chapter 18

Chapter 18. Object Database Management Systems. Outline. Motivation for object database management Object-oriented principles Architectures for object database management Object database definition and manipulation in SQL:2003 Object database definition and manipulation in Oracle 10g.

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Chapter 18

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  1. Chapter 18 Object Database Management Systems

  2. Outline • Motivation for object database management • Object-oriented principles • Architectures for object database management • Object database definition and manipulation in SQL:2003 • Object database definition and manipulation in Oracle 10g

  3. Motivation: Complex Data • Most relational DBMSs support only a few data types. • Many business applications require large amounts of complex data such as images, audio, and video. • Integration of complex data with simple data drives the demand for object database technology

  4. Motivation: Type System Mismatch • Increasing use of database access in procedural code • Different data types used in programming languages versus DBMSs • Data type mismatch makes software more difficult to develop. • A relational DBMS cannot perform elementary operations on complex data.

  5. Application Examples • Dental Office Support • Real Estate Listing Service • Auto Insurance Claims

  6. Object-Oriented Principles • An object is a combination of data and procedures. • A class is a prototype that defines the variables and methods common to all objects of the class. • Three underlying principles: encapsulation, inheritance and polymorphism.

  7. Encapsulation • Objects can be accessed only through their interfaces. • Classes can be reused rather than just individual procedures. • More complex classes can be defined using simpler classes. • Provides a form of data independence.

  8. Bond Class Example CLASS Bond { // VARIABLES: ATTRIBUTE Float IntRate; ATTRIBUTE Date Maturity; // METHODS: Float Yield(); // Computes the Bond’s Yield };

  9. Inheritance • Sharing of data and code among similar classes (classes and subclasses). • Inherit variables and methods from parent classes • Use methods and variables of ancestor classes • Provides an improved organization of software and incremental reusability.

  10. Inheritance Examples

  11. Multiple Inheritance Example

  12. Polymorphism • Ability to choose among multiple implementations • Benefits • Incremental modification of code • Smaller vocabulary of method names • Requesting a method execution involves sending a message to an object • Client-server processing and object-oriented computing are closely related.

  13. Processing a Message

  14. Binding • Associating an implementation with a message • Static binding • Performed at compile-time • More efficient but less flexible • Dynamic binding • Performed at run-time (late binding) • More flexible but less efficient

  15. Strong Type Checking • Complex expressions can involve many methods and objects • Incompatibility errors common in code • Ability to ensure that programming code contains no incompatibility errors • An important kind of error checking for object-oriented coding

  16. Programming Languages versus DBMSs • Programming languages have used object-oriented principles for many years. • Programming languages emphasize software maintenance and code reusability. • Object DBMSs are more recent. • Relax encapsulation to reference an object’s data in a query. • Simpler inheritance mechanisms in DBMSs

  17. Object Database Architectures • Adding object-oriented features to a DBMS is a good idea • Many approaches about the features to add and how features should be added. • Some approaches provide small extensions that leave object features outside the DBMS. • Other approaches involve a complete rewrite of the DBMS to accommodate objects • Marketplace will determine best approaches

  18. Large Objects and External Software • Large object storage along with external software to manipulate large objects • BLOB and CLOB data types • The large object approach is simple to implement and universal. • The large object approach suffers from serious performance drawbacks.

  19. Large Object Architecture

  20. Specialized Media Servers • Dedicated server manages complex data • Application programming interface (API) to access complex data. • Good performance for specific kinds of complex data • Limited range of operations supported • Poor performance when combining simple and complex data

  21. Specialized Media Server Architecture

  22. Object database middleware • Middleware to manage complex data stored outside of a database along with traditional data stored in a database • Integrate complex data stored on PCs and remote servers with relational databases • Possible performance problems because of a lack of integration with a DBMS.

  23. Object Middleware Approach

  24. Object-Relational DBMS • A relational DBMS extended with an object query processor for user-defined data types • User-defined types for complex data • User-defined functions in SQL statements • SQL:2003 standard • Good integration of complex data with reliability of relational DBMS

  25. Component Architecture for Object Relational DBMSs

  26. Typical User-Defined Types • Audio • Video • Text • Image • Spatial • Time series • XML

  27. Other Object Features • Subtable families • Reference and row data types • Nested tables

  28. Object-Oriented DBMS • A new kind of DBMS designed especially for objects. • Object-oriented DBMSs have an object query processor and an object kernel. • The Object Data Management Group (ODMG) provides the standard for object-oriented DBMSs.

  29. Component Architecture for Object-Oriented DBMSs

  30. Summary of Architectures • Market niche for each architecture • Simpler architectures less popular over time • Object database middleware coexist with other approaches • Object-relational approach dominates object-oriented approach

  31. SQL:2003 Object Features • Very large standard • Core language part • Parts and packages for non core features • Details about basic and enhanced object support • Two levels of conformance

  32. SQL:2003 Parts • Core parts (1,2,11): framework, foundation, schemas • Non core parts • Call level interface • Persistent stored modules • Management of external data • Object level bindings • XML specifications

  33. SQL:2003 Packages • Enhanced data-time facilities • Enhanced integrity management • Basic object support • Enhanced object support • Active databases • OLAP facilities

  34. User-Defined Types • Bundles data and procedures • Support definition of structured types, not just extensions of standard types • Use as data types for columns in tables, passed as parameters, and returned as values • User-defined functions can be used in expressions in the SELECT, the WHERE, and the HAVING clauses.

  35. User-Defined Type Example

  36. Explicit Methods • Return single values and use input parameters • Implicit first parameter: part of user-defined type • CREATE METHOD statement for method body • Mutation methods: change values • Procedures and functions not associated with types

  37. Implicit Methods • Automatically exist for all user-defined types • Constructor method: creates an empty instance • Observer methods: retrieve values • Mutation methods: change values

  38. User-Defined Type Usingan Array Example 2: Triangle type using an ARRAY CREATE TYPE Triangle AS ( Corners Point ARRAY[3], Color INTEGER ) METHOD Area() RETURNS FLOAT, -- Computes the area METHOD Scale (Factor FLOAT) RETURNS Triangle -- Computes a new triangle scaled by factor NOT FINAL;

  39. User-Defined Type Using a Multiset Example 3: Polygon type using an ARRAY CREATE TYPE Triangle AS ( Corners Point MULTISET, Color INTEGER ) METHOD Area() RETURNS FLOAT, -- Computes the area METHOD Scale (Factor FLOAT) RETURNS Polygon -- Computes a new polygon scaled by factor NOT FINAL;

  40. Table Definitions • Traditional style: foreign keys to link tables • Typed tables: supports object identifiers and object references • Row type constructor: supports rows as variables and parameters

  41. Row Type Usage

  42. User-Defined Type Usage

  43. Subtable Families • A table can be declared as a subtable of another table. • A subtable inherits the columns of its parent tables. • SQL:2003 limits inheritance for tables to single inheritance. • Set inclusion determines the relationship of a table to its subtables.

  44. Subtable Example

  45. Subtable Side Effects • Subtable insert: corresponding row is inserted into each ancestor table. • Parent update: column updated in all direct and indirect subtables • Inherited column update: column is changed in each ancestor table • Deletion: every corresponding row in both parent and subtables is also deleted.

  46. Manipulating Complex Objects and Subtable Families • Path expressions to manipulate columns with row references. • References to methods in expressions using the dot notation • Testing membership in a specific table without being a member of any subtables.

  47. Using the ROW Keyword

  48. Obtaining Object Identifiers

  49. Path Expression Example

  50. Oracle 10g Object Features • Supports most parts of the SQL:2003 object packages • User-defined types • Typed tables • Other object features

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