oriented Object DataBase
Prof. Sin-Min Lee Department of Computer Science
Object Database Systems
Not a new concept research dates back to the mid-1970s As the technology matured, a number of commercial ODBMSs appeared in the 80s and early 90s To compete with RDBMSs, it became clear that a standard for ODBMSs, analogous to SQL, was needed
Object-Oriented and Multimedia Databases
The object-oriented database (OODB) contains both the text data of traditional databases plus information about the set of actions that can be taken on the data fields. Many OODBs are multimedia databases that include graphics, audio information and animation.
Object Orientation
Modeling and development methodology A set of design and development principles based on objects Objects self-contained, reusable modules that contain data as well as their procedures
OOP Object oriented Programming
OO concepts in Ada, Algol, LISP, SIMULA OOPLs Smalltalk, C++, Java Provide for
SW development environment SW modeling tool Reduce the amount of code Reusable code
Objects
Data and procedures bound together form an Object Data is no longer passive The object can act on itself (recursive)
OOP Terminology
Object Identity (OID) Attributes (Instance variables) Object State Messages and Methods Encapsulated Structure
The ability to hide the object's internal details
OOP Terminology
Object Class
the logical structure of an object (name, attributes, methods)
Object Class Library
a group of object classes
Object
an instance of an object class
Protocol
collection of messages
OOP Terminology
Superclasses Subclasses Inheritance
Single Multiple
OOP Terminology
Polymorphism
situation in which one name can be used to invoke different functions
Inheritance
automatically assuming the attributes and methods of another object at a higher class
Object Classification
Simple object Composite object Compound object Hybrid object Associative object
OOP Example
Object Instances PERSON
Instance variables NAME ADDRESS DOB SEX AGE S S S S I
John Smith 123 Easy St 23-Nov-1970 M 32
Instance Variables ADTs
NAME FIRST_NAME S MIDDLE_NAME S LAST_NAME S
ADDRESS STREET_NUM S STREET S APARTMENT S CITY S STATE S ZIP I
DOB DAY MONTH YEAR
I I I
PERSON
SuperClass
Employee
Student
Subclasses
Representing 1:M Relationships (Premiere Products Example)
Customer SS# Name Address Balance Cred_Lim Sales_Rep 1 Sales_Rep Name Address Tot_Comm Com_Rate Customer M
Representing M:M Relationships
Manufacturer Code Name Address Contact: Person 1 Items: Item M Item Code Description Quantity Unit_Price Manufacturers: Manufacturer M
Late Binding
`A desirable characteristic of OO development is its ability to let any object's attribute contain object that define different data types (or classes) at different times. `
Late binding
Attributes Item_Type Description Vendor Weight Price RDBMS Numeric Char Numeric Numeric Numeric Instance variables Item_Type Description Vendor Weight Price OODB Inv_Type String_of_char Vendor Weight Money
OODBMS
Object-Oriented Features OODBMS Conventional DBMS
Data accessibility Persistence Backup and Recovery Transaction Processing Concurrency Security/Integrity Administration OO Concepts OO data models OOPL GUI
13 Rules for an OODBMS from the OODBS Manifesto
System must support complex objects Object identifier must be supported Objects must be encapsulated Systems must support types or classes System must support inheritance System must avoid premature binding System must be computationally complete System must be extensible
Object Database Systems
The vendors formed a consortium, the Object Database Management Group (ODMG), to define a standard Current standards specification is ODMG 2.0 Architecture has four major components a data model, a specification language, a query language, and language bindings
Object Data Model
Based upon the (Object Management Group) OMG Object Model OMG is another consortium of vendors instituted to create standards Besides an object model, they oversee standards for UML and CORBA (Common Object Request Broker Architecture)
Object Model
Two basic modeling primitives objects and literals An object has a unique identifier A literal has no identifier Every object and every literal is categorized by its type a set of values and a set of supported operations
Object Model
An object's state is characterized by a set of properties An object property can be either an attribute or a relationship to another object The set of operations that can be executed on or by an object defines the behavior of an object
Object Model
An operation may have input and/or output parameters, and may return a value The type of each parameter and the returned value must be specified A database stores objects, which can be shared by multiple users and applications A database is based on a schema, defined in the object definition language (ODL)
Types
There are two facets to the definition of a type an external specification and one or more implementations The specification of a type corresponds to what is visible to a user operations that can be applied to instances, its properties, or state variables, and any exceptions that can be raised by the operations
Types
An implementation of a type defines the internal aspects of the objects of a type how the operations access or modify the properties of an object A class definition and an interface definition may specify both the abstract behavior and the abstract state of an object
Types
A literal definition specifies only the abstract state of a literal type An implementation of an object type consists of a representation and a set of methods The representation is a data structure realizing the abstract state of an object or literal, expressed in a language binding
Types
Each property is represented by an instance variable The operations of an object type are implemented as procedures expressed in a language binding The internal details of an implementation are invisible to the user
Inheritance
Inheritance is a second important characteristic of object orientation The data model supports two constructs supporting inheritance interfaces and classes Interfaces permit the definition of subtypes A subtype represents the specialization of a more general type (the supertype)
Inheritance
The generalization/specialization is relationship often called an "is-a" relationship Interfaces are abstract types they cannot be instantiated The data model supports multiple inheritance of interfaces
Inheritance
Classes support a second form of inheritance, described as the "extends" relationship A class can extend the behavior and state of another class Classes can be instantiated An object is an instance of a class
Inheritance
Classes support only single inheritance An interface can inherit from another interface, but not from a class A class can inherit from multiple interfaces and can extend a single class Objects have a number of characteristics identifiers, names, lifetimes, and structures
Identifiers
Unlike the relational model, objects within a database are assigned unique identifiers An identifier is generated by the database system when the object is created They are immutable although the properties of a object may change, its identifier remains the same throughout its lifetime
Names
Object identifiers are commonly used for one object to refer to another An object may also have a name Applications typically refer to some objects by a user-defined name The database internally maps names to identifiers
Lifetimes
The lifetime of an object is specified when it is created The are two possible lifetimes persistent and transient A transient object is allocated memory by an application's runtime system A transient object's lifetime is the lifetime of the procedure or process that creates it
Lifetimes
Persistent objects are allocated memory and secondary storage that is managed by the ODBMS runtime system A persistent object exists after the process that created it terminates Persistent objects also called database objects Object types and lifetimes are independent
Collection Objects
The data model supports a number of container types to store collections of objects All elements of a collection must be of the same type Set object an unordered collection with no duplicates
Collection Objects
Bag object an unordered collection that may contain duplicate objects List object an ordered collection of elements Array object another kind of ordered collection of objects Both lists and arrays are position-oriented
Collection Objects
The insertion and removal operations take argument specifying the position at which the element is to be inserted or deleted Both collections are zero-based Removing an element from a list changes the positions of elements in the list tail Removing an element from an array simply replaces the element with a null value
Modeling an Object's State
Two kinds of properties attributes and relationships An attribute is defined to be of a single type Its type may be either a literal or a class Relationships define associations between two types The data model supports only binary relationships
Modeling an Object's State
Relationships are defined implicitly by specifying traversal paths Traversal paths are always declared in pairs This permits bidirectional traversal from either object in the association The ODBMS is responsible for maintaining the referential integrity of a relationship
Modeling an Object's State
The connectivity of a relationship may be one-to-one, one-to-many, or many-to-many The connectivity is always clear from the syntax of the declaration of a relationship To represent arbitrary n-ary relationships, a designer would create a new class type, each instance of which would represent an n-tuple
Object Definition Language
The Object Definition Language (ODL) is used to define the specification of object types Roughly corresponds to the DDL of SQL A designer uses ODL to define a database schema
Structured Types
struct Address { string street; string city; string s...