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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:1999 Object database definition and manipulation in Oracle 9i 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. The need to integrate complex data with simple data drives the demand for object database technology. 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. Application Examples Dental Office Support Real Estate Listing Service Auto Insurance Claims 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. 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. Bond Class Example CLASS Bond { // VARIABLES: ATTRIBUTE Float IntRate; ATTRIBUTE Date Maturity; // METHODS: Float Yield(); // Computes the Bond’s Yield }; Inheritance Sharing of data and code among similar classes (classes and subclasses). Inherit variables and methods from parent classes When using the subclasses, the methods in the parent classes can be used. Inheritance provides an improved organization of software and incremental reusability. Inheritance Examples Bond IntRate Maturity Yield Point x,y Distance Equals Inheritance Relationships ColorPoint Color Brighten SubClasses Corporate Rating TheCompany Junk Multiple Inheritance Example Security Symbol SecName LastClose Stock OutShares IssuedShares Yield Inheritance conflict Bond IntRate Maturity Yield Convertible ConvPrice ConvRatio Polymorphism Ability of a computing system to choose among multiple implementations Benefits – Fewer, more reusable methods – incremental modification of code Requesting a method execution involves sending a message to an object Client-server processing and objectoriented computing are closely related. Processing a Message Point class Distance code Message forwarded to parent class Message sent to ColorPoint object (CP1) to compute distance ColorPoint class CP1 object 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 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 Programming Languages versus DBMSs Programming languages have used objectoriented principles for many years. Programming languages emphasize software maintenance and code reusability. Object DBMSs are more recent. Encapsulation usually is relaxed so that an object’s data can be referenced in a query. Inheritance mechanisms usually are simpler in DBMSs Architectures for Object Database Management 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 Large Objects and External Software Storage of large objects in a database along with external software to manipulate large objects. Complex data are stored in a field using the BLOB (binary large object) data type. The large object approach is simple to implement and universal. The large object approach suffers from serious performance drawbacks. Large Object Architecture External software for manipulating complex data SQL statements Simple and complex data Simple data Complex data Database server Relational database Specialized Media Servers The use of a dedicated server to manage complex data outside of a database. Programmers use an application programming interface (API) to access complex data. Provide good performance for specific kinds of complex data. The range of operations may be limited. May perform poorly when combining simple and complex data. Specialized Media Server Architecture SQL statements and results API calls and results Database Database server Media server Media base Object database middleware The use of middleware to manage complex data stored outside of a database along with traditional data stored in a database. Provides a way to integrate complex data stored on PCs and remote servers with relational databases. Object middleware can suffer performance problems because of a lack of integration with a DBMS. Object Middleware Approach SQL statements and results Object middleware SQL statements and results Database Database server API calls and results Media server Media base Object Relational DBMS for User-Defined Types A relational DBMS extended with an object query processor for user-defined data types. Complex data is added as a user-defined type. User-defined functions can be defined and then used in SQL statements. SQL:1999 provides the standard for object relational DBMSs. Provide good integration of complex data but reliability may be a concern. Component Architecture for Object Relational DBMSs SQL statements and results Object query processor (parser, optimizer, display manager) API calls and results Relational kernel (transaction processing, storage management, buffer management) Database 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 objectoriented DBMSs. Component Architecture for Object-Oriented DBMSs OQL statements and results Object query processor (parser, optimizer, display manager) API calls and results Relational kernel (transaction processing, storage management, buffer management) Database Summary of Architectures Architecture Large objects Example Products Comments Most SQL-92 DBMSs Media servers Oracle 7.3 with text and spatial data servers Object database Microsoft middleware Universal Data Access Object relational IBM UniData Data (SQL3) Blades, IBM DB2 Extenders, Oracle 9i Object-oriented (ODMG) Poor performance; no query language support; universal storage capability No query language support; poor performance involving simple and complex data; good performance on complex data Uncertain performance when combining simple and complex data; Ability to combine diverse data sources Uncertain reliability; good query language support; some type mismatch with programming languages; good support with specialized storage structures ObjectStore, Good query language support; uncertain UniSQL, O2, performance for traditional applications; Versant, Gemstone good type match with programming languages Object Database Features in SQL:1999 Very large standard Core language part Packages Details about basic and enhanced object support Two levels of conformance SQL:1999 Packages SQL3 Package Core Scope SQL environment, SQL implementation, tables, views, predefined data types, SQL statements, conformance specifications Persistent Stored Modules Computational completeness, stored modules, function overloading Call Level Interface Call interface for SQL Enhanced Datetime Time zone specification, interval data type Facilities Enhanced Integrity Assertions, triggers, constraint management Management OLAP Facilities Cube and roll-up operators, row and table constructors, FULL JOIN and INTERSECT operators Basic Object Support User-defined data types, single inheritance, reference types, arrays Enhanced Object Support Path expressions, subtable definition, subtable search, subtypes User-Defined Types Bundles data and procedures Support definition of structured types, not just extensions of standard types User-defined types can be used 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. User-Defined Type Example Example 1: Point Type CREATE TYPE Point AS ( x FLOAT, -- X coordinate y FLOAT ) -- Y coordinate METHOD Distance(P2 Point) RETURNS FLOAT, -- Computes the distance between 2 points METHOD Equals (P2 Point) RETURNS BOOLEAN -- Determines if 2 points are equivalent NOT FINAL INSTANTIABLE; Explicit Methods Return single values and use input parameters Implicit first parameter: part of userdefined type CREATE METHOD statement for method body Mutation methods: change values Procedures and functions not associated with types Implicit Methods Automatically exist for all user-defined types Constructor method: creates an empty instance Observer methods: retrieve values Mutation methods: change values User-Defined Type using an Array Example 2: Polygon type using an ARRAY CREATE TYPE Polygon AS ( Corners Point ARRAY[10], Color INTEGER ) METHOD Area() RETURNS FLOAT, -- Computes the area METHOD Scale (Factor FLOAT) RETURNS Polygon -- Computes a new polygon scaled by factor NOT FINAL; 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 Example of table definition with a row type Example 3: Property table definition with a row type CREATE TABLE Property (PropNo INTEGER, Address ROW (Street VARCHAR(50), City VARCHAR(30), State CHAR(2), Zip CHAR(9) ), SqFt INTEGER, View BLOB, AgentNo INTEGER, Location Point, CONSTRAINT PropertyPK PRIMARY KEY(PropNo), CONSTRAINT AgentFK FOREIGN KEY(AgentNo) REFERENCES Agent ); Table Definition with a UserDefined Type Example 4: Definition of AgentType, followed by the Agent table based on AgentType CREATE TYPE AddressType AS (Street VARCHAR(50), City VARCHAR(30), State CHAR(2), Zip CHAR(9) ) NOT FINAL; CREATE TYPE AgentType AS (AgentNo INTEGER, Name VARCHAR(30), Address AddressType, Phone CHAR(13), Email VARCHAR(50) ) NOT FINAL; CREATE TABLE Agent OF AgentType (REF IS AgentOId SYSTEM GENERATED, CONSTRAINT AgentPK PRIMARY KEY(AgentNo) ); Subtable Families A table can be declared as a subtable of another table. A subtable inherits the columns of its parent tables. SQL:1999 limits inheritance for tables to single inheritance. Set inclusion determines the relationship of a table to its subtables. Subtable Example Example 5: Subtable of Property Table CREATE TYPE ResidentialType UNDER PropertyType (BedRooms INTEGER, BathRooms INTEGER, Assessments DECIMAL(9,2) ARRAY[6] ) NOT FINAL INSTANTIABLE; CREATE TABLE Residential OF ResidentialType UND Property; CREATE TYPE IndustrialType UNDER PropertyType (Zoning VARCHAR(20), AccessDesc VARCHAR(20), RailAvailable BOOLEAN, Parking VARCHAR(10) ) NOT FINAL INSTANTIABLE; CREATE TABLE Industrial OF IndustrialType UNDER Property; Side effects when manipulating rows in subtable families On insert into a subtable, a corresponding row is inserted into each parent table. On update in a parent table, the column is also updated in all direct and indirect subtables that inherit the column. On update of an inherited column, the column is changed in the corresponding rows of direct and indirect parent tables. On delete, every corresponding row in both parent and subtables is also deleted. 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. Using the ROW Keyword Example 6: Using the ROW keyword in an INSERT statement. INSERT INTO Agent (AgentNo, Name, Address, Email, Phone) VALUES (999999, 'Sue Smith', ROW('123 Any Street', 'Denver', 'CO', '80217'), '[email protected]', '13031234567') Example 7: Using a type name in an INSERT statement. INSERT INTO Agent (AgentNo, Name, Address, Email, Phone) VALUES (999999, 'Sue Smith', AddressType('123 Any Street', 'Denver', 'CO', '80217'), '[email protected]', '13031234567'); Obtaining Object Identifiers Example 8: Using a SELECT statement to retrieve the object identifier of the related Agent row. INSERT INTO Residential (PropNo, Address, SqFt, AgentRef, BedRooms, BathRooms, Assessments) SELECT 999999, AddressType('123 Any Street', 'Denver', 'CO', '80217'), 2000, AgentOID, 3, 2, ARRAY[190000, 200000] FROM Agent WHERE AgentNo = 999999; Example of path expression versus traditional expression Example 9: SELECT statement with path expressions and the dereference operator SELECT PropNo, P.Address.City, P.AgentRef->Address.City FROM Property P WHERE AgentRef->Name = 'John Smith' Oracle 9i Object Features Supports most parts of the SQL:1999 object packages User-defined types Typed tables Other object features User-Defined Type Example Example 10: Point type in Oracle 9i CREATE TYPE Point AS OBJECT ( x FLOAT(15), y FLOAT(15), MEMBER FUNCTION Distance(P2 Point) RETURN NUMBER, -- Computes the distance between 2 points MEMBER FUNCTION Equals (P2 Point) RETURN BOOLEAN, -- Determines if 2 points are equivalent MEMBER PROCEDURE Print ) NOT FINAL INSTANTIABLE; Inheritance Example 11: ColorPoint type in Oracle 9i CREATE TYPE ColorPoint UNDER Point (Color INTEGER, MEMBER FUNCTION Brighten (Intensity INTEGER) RETURN INTEGER, -- Increases color intensity MEMBER FUNCTION Equals (CP2 ColorPoint) RETURN BOOLEAN, -- Overriding is not used because the two -- Equals methods have different signatures. OVERRIDING MEMBER PROCEDURE Print ) NOT FINAL INSTANTIABLE; Typed Tables Example 12: Typed table example CREATE TYPE PropertyType AS OBJECT (PropNo INTEGER, Address AddressType, SqFt INTEGER, AgentRef REF AgentType, Location Point ) NOT FINAL INSTANTIABLE; CREATE TABLE Property OF PropertyType ( CONSTRAINT PropertyPK PRIMARY KEY(PropNo), CONSTRAINT AgentRefFK FOREIGN KEY(AgentRef) REFERENCES Agent ) OBJECT IDENTIFIER IS SYSTEM GENERATED ; Inheritance for Typed Tables Example 13: Typed table example with inheritance CREATE TYPE AssessType AS VARRAY(6) OF DECIMAL(9,2); CREATE TYPE ResidentialType UNDER PropertyType (BedRooms INTEGER, BathRooms INTEGER, Assessments AssessType ) NOT FINAL INSTANTIABLE; CREATE TABLE Residential OF ResidentialType (CONSTRAINT ResidentialPK PRIMARY KEY(PropNo), CONSTRAINT AgentRefFK1 FOREIGN KEY(AgentRef) REFERENCES Agent ) OBJECT IDENTIFIER IS SYSTEM GENERATED ; Inserting into Typed Tables Example 14: Insert rows into the residential and property tables INSERT INTO Residential (PropNo, Address, SqFt, AgentRef, BedRooms, BathRooms, Assessments) SELECT 999999, AddressType('123 Any Street', 'Denver', 'CO', '80217'), 2000, REF(A), 3, 2, AssessType(190000, 200000) FROM Agent A WHERE AgentNo = 999999; INSERT INTO Property (PropNo, Address, SqFt, AgentRef) SELECT 999999, AddressType('123 Any Street', 'Denver', 'CO', '80217'), 2000, REF(A) FROM Agent A WHERE AgentNo = 999999; Path Expressions Example 15: Path expression using the DEREF function SELECT PropNo, P.Address.City, DEREF(AgentRef).Address.City FROM Property P WHERE DEREF(AgentRef).Name = 'John Smith'; Example 16: Path expression using the dot operator SELECT PropNo, P.Address.City, P.AgentRef.Address.City FROM Property P WHERE P.AgentRef.Name = 'John Smith'; Other Object Features Type substitutability for subtables Hierarchical views Nested tables Summary Three principles of object-oriented computing guide the development of object DBMSs. A number of object DBMS architectures are commercially available. SQL:1999 supports definition and manipulation of object relational databases. Oracle 9i is a significant implementation of the SQL:1999 object packages