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ADVANCED DATABASES. ODMG Object Model, Object Definition Language (ODL). Khawaja Mohiuddin Assistant Professor Department of Computer Sciences Bahria University (Karachi Campus) [email protected] https://sites.google.com/site/khawajamcs.

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odmg object model object definition language odl
ADVANCED DATABASESODMG Object Model,Object Definition Language (ODL)

Khawaja Mohiuddin

Assistant Professor

Department of Computer Sciences

Bahria University (Karachi Campus)

[email protected]

https://sites.google.com/site/khawajamcs

Contents for this lecture are taken from:

Chapter 10 of “Database Systems: Models, Languages …”, 6th Ed.” by Elmasri and Navathe

(Chapter 11 of “Fundamentals of Database Systems” 6th Ed. by Elmasri and Navathe)

objectives
Objectives
  • To get to know how Object Data Management Group (ODMG) was formed
  • To understand the ODMG modeling terminology
  • To learn how Interfaces and Classes are defined in ODMG object model
  • To learn how Objects are inherited
  • To know the built-in Interfaces and Classes in ODMG object model
  • To understand the Object Definition Language (ODL)
  • To learn the graphical notations used in ODL
the odmg object model
The ODMG Object Model
  • Many experimental ODBMS prototypes created:
    • Orion system by MCC, OpenOODB by Texas Instruments, Iris system by Hewlett-Packard laboratories, Ode system by AT&T Bell Labs, ENCORE/ObServer project at Brown University, etc.
  • Many Commercial ODBMS are available:
    • GemStone Object Server of GemStone Systems, ONTOS DB of Ontos, Objectivity/DB of Objectivity Inc., Versant Object Database and FastObjects by Versant Corporation, ObjectStore of Object Design, and Ardent Database of Ardent, etc.
  • Because of the popularity of relational and object-relational systems, ODMS did not find widespread use.
the odmg object model cont d
The ODMG Object Model (cont’d.)
  • The lack of a standard for ODMS for several years may also have caused some potential users to shy away from converting to this new technology.
  • Need for a standard model and language was recognized.
  • A consortium of object DBMS vendors and users, called Object Data Management Group(ODMG), proposed a standard whose current specification is known as the ODMG 3.0 standard.
  • The standard includes the object model, the object definition language (ODL), the object query language (OQL), and the bindings to object-oriented programming languages.
the odmg terminology
The ODMG Terminology
  • ODMG object model is meant to provide a standard data model for object databases, just as relational model describes a standard data model for relational databases
  • Objects and Literals
    • Basic building blocks of the object model
    • Object has both object identifier and state (current value)
    • literal has a state (value) but no object identifier
    • Object’s state changes, literal’s does not
the odmg terminology cont d
The ODMG Terminology (cont’d.)
  • Object has five aspects:
    • Identifier
      • a unique system-wide identifier (Object_id)
      • every object must have an object identifier
    • Name
      • an object may be given a unique name
      • not all individual objects will have names
      • mainly objects that hold collections of objects (extents) will have a name.
      • these names are used as entry points to the database
      • the user can then locate other objects that are referenced from these objects
      • it is possible to give more than one name to an object
      • all names within a particular ODMS must be unique
the odmg terminology cont d1
The ODMG Terminology (cont’d.)
  • Lifetime
    • specifies whether persistent object or transient object
    • persistent object is a database object
    • transient object is an object in an executing program that disappears after the program terminates
    • lifetimes are independent of types (some may be transient whereas others may be persistent for same type)
  • Structure
    • specifies how object is constructed by using type constructors
    • specifies whether an object is atomic or not
    • atomic object refers to a single object that follows a user-defined type, such as Employee or Department
the odmg terminology cont d2
The ODMG Terminology (cont’d.)
  • Structure (cont’d.)
    • if not atomic, then object will be composed of other objects. Example: collection object
    • atomic object is different from atom constructor covered in Section 11.1.3, which referred to all values of built-in data types
  • Creation
    • refers to the manner in which an object can be created
    • typically accomplished via an operation new for a special Object_Factory interface
    • (Will cover in more detail later)
the odmg terminology cont d3
The ODMG Terminology (cont’d.)
  • Literal
    • Value that does not have an object identifier
    • value may have a simple or complex structure
    • Three types of literals: atomic, structured, and collection
      • Atomic literals correspond to the values of predefined, basic data types. Example: long, short, float, boolean, char, string, etc.
      • Structured literals correspond roughly to values constructed using tuple constructor, include built-in structured literals like Date, Interval, Time, etc. and user-defined structured literals defined as needed by each application
      • Collection literals specify a literal value that is a collection of objects or values. The collection itself does not have an Object_id
the odmg terminology cont d4
The ODMG Terminology (cont’d.)
  • Behavior refers to operations
  • State refers to properties (attributes and relationships)
  • Interface
    • Specifies only behavior of an object type
    • Typically noninstantiable(no objects are created corresponding to an interface)
    • May have state properties (attributes and relationships), but these cannot be inherited
    • Serves to define operations that can be inherited by other interfaces and classes
the odmg terminology cont d5
The ODMG Terminology (cont’d.)
  • Class
    • Specifies both state (attributes) and behavior (operations) of an object type
    • Instantiable(objects can be created)
    • objects are typically created based on the user-specified class declarations that form a database schema
interface and class definitions in odmg
Interface and Class Definitions in ODMG
  • interface Object {
  • ...
  • booleansame_as(in object other_object);
  • object copy();
  • void delete();
  • };
  • Class Date : Object {
  • enum Weekday
  • {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday};
  • enum Month
  • {January, February, March, April, May, June,
  • July, August, September, October, November, December };
  • unsigned short year();
  • unsigned short month();
  • unsigned short day();
  • ...
  • booleanis_equal(in Date other_date); ... };
interface and class definitions in odmg cont d
Interface and Class Definitions in ODMG (cont’d.)

interface Collection : Object {

...

exception ElementNotFound{ Object element; };

unsigned long cardinality();

booleanis_empty();

...

booleancontains_element(in Object element);

void insert_element(in Object element);

void remove_element(in Object element)

raises(ElementNotFound);

iteratorcreate_iterator(in boolean stable);

... };

interface set : Collection {

set create_union(in set other_set);

...

booleanis_subset_of(in set other_set);

... };

inheritance in the object model of odmg
Inheritance in the Object Model of ODMG
  • Behavior inheritance
    • Also known as IS-A or interface inheritance
    • Specified by the colon (:) notation
    • Requires the supertype to be an interface
    • Multiple inheritance is allowed
  • EXTENDS inheritance
    • Specified by keyword extends
    • Inherit both state and behavior strictly among classes
    • Multiple inheritance via extends not permitted
built in interfaces and classes in the object model
Built-in Interfaces and Classes in the Object Model
  • Collection objects
    • Inherit the basic Collection interface
  • I = O.create_iterator()
    • Creates an iteratorobject Ifor the collection object O
  • Collection objects further specialized into:
    • set, list, bag, array, and dictionary
atomic user defined objects
Atomic (User-Defined) Objects
  • Specified using keyword class in ODL
  • Attribute
    • Property; describes some aspect of an object
  • Relationship
    • Two objects in the database are related
    • Only binary relationships are explicitly represented
    • Keyword inverse
      • Specifies that two properties define a single conceptual relationship in inverse directions
  • Operation signature:
    • Operation name, argument types, return value
atomic user defined objects cont d
Atomic (User-Defined) Objects (cont’d.)

class EMPLOYEE

( extent ALL_EMPLOYEES

key Ssn )

{

attribute string Name;

attribute string Ssn;

attribute date Birth_date;

attribute enum Gender{M, F} Sex;

attribute short Age;

relationship DEPARTMENT Works_for

inverse DEPARTMENT::Has_emps;

void reassign_emp(in string

New_dname)

raises(dname_not_valid);

};

class DEPARTMENT

( extent ALL_DEPARTMENTS

key Dname, Dnumber )

{

attribute string Dname;

attribute short Dnumber;

attribute structDept_mgr {EMPLOYEE

Manager, date Start_date}

Mgr;

attribute set Locations;

attribute structProjs {string

Proj_name, time Weekly_hours)

Projs;

relationship set Has_emps

inverse EMPLOYEE::Works_for;

void add_emp(in string New_ename) raises(ename_not_valid);

void change_manager(in string New_mgr_name; in date

Start_date); };

extents keys and factory objects
Extents, Keys, and Factory Objects
  • Extent
    • Contains all persistent objects of class
    • Behaves as a set object (see EMPLOYEE class)
  • Key
    • One or more properties whose values are unique for each object in extent
    • A class with an extent can have one or more keys (see DEPARTMENT class)
  • Factory object
    • Used to generate or create individual objects via its operations (provides constructor operations)
more on factory objects
More on Factory Objects
  • By inheriting this interface, users can create their own factory interfaces for each user-defined (atomic) object type, and can implement the operation new differently for each type of object

interface ObjectFactory {

Object new();

};

interface SetFactory : ObjectFactory {

Set new_of_size(in long size);

};

interface ListFactory : ObjectFactory {

List new_of_size(in long size);

};

interface ArrayFactory : ObjectFactory {

Array new_of_size(in long size);

};

the object definition language odl
The Object Definition Language ODL
  • Support semantic constructs of ODMG object model
  • Its main use is to create object specifications, i.e. classes and interfaces
  • Independent of any particular programming language
summary
Summary
  • Overview of concepts utilized in ODMG object model
    • Object identity and identifiers; operations; inheritance; complex structure of objects through nesting of type constructors; and how objects are made persistent
  • Description of the ODMG object model and object Definition language (ODL)
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