Transcript CSE 494 - Villanova University

OBJECT-ORIENTED DATABASE SYSTEMS
ODMG Standard: Object Model
Susan D. Urban and Suzanne W. Dietrich
Department of Computer Science and Engineering
Arizona State University
Tempe, AZ 85287-5406
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Object Model
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OUTLINE
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Purpose of ODMG
Components of ODMG
Basic Modeling Concepts
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Object Model
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CURRENT STATE OF OBJECT MODELS
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Unlike the relational model, commercial OODB's were
developed before any formal, standard basis was
established for object models.
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A proliferation of commercial tools with some similarities and also
with differences. Makes portability difficult.
Has been difficult to establish a standard approach to query
languages for OODB's with formal semantics to support query
optimization.
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Object Model
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STANDARDS OF OBJECT MODELS
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Standards for object models are now being developed to
promote portability and interoperability between tools.
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The Object Data Management Group Standard (ODMG).
The Object Management Group Standard (OMG).
SQL99 Standard (Extended Relational).
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Object Model
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THE ODMG STANDARD
Purpose
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Major goal is to establish standards that allow OODB
customers to write portable applications that can run on
more than one OODB product.
Supported by major OODB vendors and users.
The data schema, programming language binding, and data
manipulation and query language must be portable.
Differences will always exist in performance, languages
supported, specific functionality (e.g., versioning),
programming environments, application construction tools,
networking, predefined libraries, etc.
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THE ODMG STANDARD
Components
Major components of the standard include:
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An Object Model - Defines the basic components of an
object model.
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An Object Definition Language - Defines a data definition
language, known as ODL (for Object Definition
Language).
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An Object Query Language - Defines a declarative object
query language (OQL) for querying and updating objects.
OQL has an extended SQL flavor.
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THE ODMG STANDARD
Programming Languages Support
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A C++ Language Binding - Supports portable C++ code
for manipulating objects. The language is called the C++
Object Manipulation Language (OML).
A Smalltalk Language Binding - Have drafted similar
bindings to support the development of portable code in
Smalltalk.
A Java Language Binding – Java bindings are now
available.
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USING THE ODMG STANDARD
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BASIC MODELING CONCEPTS
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Basic modeling primitives are the object (has a unique
object identifier - OID) and the literal (has no identifier).
An OID is immutable (the value of an OID for a particular
object cannot change).
Objects are categorized into types.
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A type has an interface (properties and operations).
A type has one or more implementations.
An implementation defines data structures (physical
representations of objects) and/or methods.
Behavior of objects is defined by a set of operations.
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OBJECT PROPERTIES
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Object states are defined by properties, which are:
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attributes (string, integer, etc. as values, including objects), or
relationships (other objects as values with inverse traversal path
specified and integrity maintained by the db)
The state of an object is mutable (the value of attributes
and relationships can change).
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TYPES AND EXTENTS
Types are objects and thus have properties:
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Supertypes and subtypes
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The subtypes of a supertype can define additional operations and
properties.
Subtypes can refine properties and operations.
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Supports multiple inheritance.
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Extents
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The set of all instances of a type.
Can optionally request that the system maintain the extent
automatically.
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OBJECT CLASSES
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A type interface plus an implementation defined for the
type is a class.
A class in ODMG is similar to a class in C++.
C++ class
a public part
a private part
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•••
ODMG class
attributes and relationships
implementation
A class can define keys.
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Same as in the relational model.
Single keys or composite keys.
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THE ODMG BUILT-IN TYPE HIERARCHY
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Object
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Atomic Object
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Literal
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Long, Short,
Unsigned long,
Unsigned short, Float,
Double, Boolean, Char,
Octet, String, Enum <>
Collection <T>, Set <T>,
Bag <T>, List <T>
Array <T>.
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Structured_literal
Date, Time, Timestamp,
Interval, Structure <>
Atomic_Literal
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Collection_literal <T>
Set <T>, Bag <T>,
List<T>, Array <T>
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Structured_literal
Date, Time, Timestamp,
Interval, Structure <>
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NAMING AND LIFETIME
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Objects can have names (i.e., meaningful or logical OID's).
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Names can also be viewed as handles that allow users to easily
reference a specific object.
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Objects have lifetimes.
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transient (allocated in memory only)
persistent (stored on disk)
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ODL SYNTAX SUMMARY FOR CLASSES
class c_name [extends superclass_name]
( extent extent_name
key key_name
)
{ attribute <attribute_type> attribute_name;
…
relationship <relation_type> relation_name
inverse <inverse_spec>;
…
method_definitions;
}
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HOLLYWOOD SCHEMA IN ODL
class Person
class Person
( extent persons
key ssn)
{
attribute string ssn;
attribute string name;
attribute string gender;
attribute string phone;
attribute string address;
relationship Person isMarriedTo inverse …;
void createPerson(in string ssn, in string name, in string gender, in string phone,
in string address);
void deletePerson();
. . .
}
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HOLLYWOOD SCHEMA IN ODL
class Celebrity
class Celebrity extends Person
( extent celebrities)
{
attribute date birthDate;
relationship Agent agent inverse Agent::celebrities;
void createCelebrity(in string ssn, in string name, in string gender, in string phone,
in string address, in date birthDate);
void deleteCelebrity();
. . .
}
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INHERITANCE OF STATE VS.
INHERITANCE OF BEHAVIOR
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Classes in ODMG 2.0 are types that can be directly
instantiated.
The extends relationship represents inheritance of state and
behavior, where the subordinate class inherits all of the
properties and behavior of the class that it extends.
Interfaces can be used to define types that cannot be
directly instantiated. Interfaces are used to define the
inheritance of behavior only.
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Interfaces may inherit from other interfaces (is-a relationship).
Classes may inherit from interfaces (is-a relationship).
Classes may inherit from other classes (the extends relationship).
Interfaces may not inherit from classes.
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SUMMARY OF SYNTAX FOR INTERFACE
CLASSES
interface i_name
{
methodDefinitions
…
}
class c_name [extends superClass]: i_name
( …)
{
…
}
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