1 ODMG. 2 Object Database Management Group (ODMG) ODMG has been formed in late 1991 by: ObjectDesign,…

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ODMG

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ODMG• Object Database Management Group

(ODMG)ODMG has been formed in late 1991 by:

ObjectDesign, Ontos, O2 Technology, Versant, Objectivity, Digital Equipment, Hewlett-Packard, Itasca, Intellitic, Poet Software, Servio, Texas Instruments

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R.G.C. Cattell The Object Database Standard : ODMG, Release 1.2, 1996

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R.G.C. Cattell The Object Database Standard : ODMG, Release 1.2, 1996

R.G.C. Cattell, D.K. Barry The Object Database Standard: ODMG 2.0, 1997

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ODMG• Aims

To put forward a set of standards allowing an ODBMS customer to write portable applications, i.e. application that could run on more than one ODBMS

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ODMG• ODMG versus Relational DBMS

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ODMG• ODMG versus Relational DBMS

Application Data Structures

Relational Representation

RDBMS

Copy and Translation Transparent

ODBMS Data Transfer

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ODMG• Architecture

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ODMG• Architecture

Declarations in ODL or Programming Language ODL

Declaration Preprocessor

metadata

Database

Application Source in extended Programming Language

Programming Language Compiler

Application Binaries

Linker

Running ApplicationData Access

OO DBMS Runtime

Fig. 1 ODMG DBMS Architecture

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ODMG• Components

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ODMG• Components

FrameworkA portion of ODMG that is common to all programming languages

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ODMG• Components

FrameworkA portion of ODMG that is common to all programming languages

Framework consist of:

»Object Model

»Object Definition Language

»Object Query Language

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ODMG• Components

Bindings

Bindings for each programming language in which ODBMS is used (currently: C++, Smalltalk)

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ODMG• Basic concepts

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The model is based on objects with object identifiers

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Objects are categorised into types

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The behaviour of objects is defined by a set of operations

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The behaviour of objects is defined by a set of operations

The state of objects is determined by a set of properties (attributes, relationships)

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Each object may have a unique name

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Operations are defined by operation signatures

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Attributes are defined by attribute signatures

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Attributes are defined by attribute signatures

Relationships are specified by relationship signatures

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Collection types include sets, bags, lists and arrays

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Object types are related in subtype/supertype graph

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Object types are related in subtype/supertype graph

An extent set can be declared to contain all instances of a given type

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Individual instances can be uniquely identified by the value they carry for some property or set of properties (keys)

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ODMG• Type hierarchy

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ODMG• Type hierarchy Denotable Object

Object Literal

Atomic Object Structured Object Atomic LiteralStructured Literal

Type

Exception

Iterator

Collection<T>

Structure <e1:T1,..., en:Tn>

Set<T> Bag<T> List<T>Array<T>

String Bit String

IntegerCharacter

BooleanFloat

Immutable Sructure <e1:T1,..., en:Tn>

Immutable Collection<T>

Immutable Set<T>

Immutable List<T>

Immutable String

Immutable Bit String

Immutable Bag<T>

Immutable Array<T>

enumeration

DateTime

Date Time

Interval

Fig. 2 The ODMG type hierarchy

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ODMG• Object Definition Language

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Employee

TeachingAssistant Professor

Section

Student

Course

teaches

is taught by

assists

has TA

has prerequisites

is prerequisite

belongs to

consists of

has

of

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interface Course( extent courses

keys name, number )

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keys name, number ){

attribute String name;attribute String number;

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attribute String name;attribute String number;relationship List<section> has_sections

inverse Section::is_section_of{ order by Section::number };

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relationship Set<Course> has_prerequisitesinverse Course::is_prerequisite_for;

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relationship Set<Course> has_prerequisitesinverse Course::is_prerequisite_for;

relationship Set<Course> is_prerequisite_forinverse Course::has_prerequisites;

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Boolean offer( in Unsigned Short semester)raises(already_offered);

Boolean drop( in Unsigned Short semester)raises(not_offered);

};

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interface Section( extent sections

key (is_section_of, number) )

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interface Section( extent sections

key (is_section_of, number) ){ attribute String number;

relationship Professor is_taught_by inverse professor::teaches;

relationship TA has_TA inverse TA::assists;

relationship Course is_section_of inverse Course::has_sections;

relationship Set<Student> is_taken_by inverse Student::takes;

};

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interface Employee( extent employees

key (name. id) ){

attribute String name;attribute Short id;attribute Unsigned Short annual_salary;

void hire();void fire() raises (no_such_employee);

};

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interface Professor:Employee( extent professors ){ attribute Enum Rank { full, associate, assistant} ;

relationship Set<Section> teachesinverse section::is_taught_by;

Short grant_tenure()raises(ineligible_for tenure);

}interface TA: Employee, Student(){

relationship Section assistsinverse Section::has_TA;

};

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interface Student( extent students

keys name, student_id ){ attribute String name;

attribute String student_id;attribute Struct Address

{ String college,String room_number,

} dorm_address;relationship Set<Section> takes

inverse Section::is_taken_by;

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ODMG• Object Definition Language)

Boolean register_for_course(in Unsigned Short Course,in Unsigned Short Section )

raises(unsatisfied_prerequisites,section_full,course_full );

void drop_course(in Unsigned Short Course )raises( not_registered_for_that_course);

void assign_major(in Unsigned Short Department );

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Short transfer( in Unsigned Short old_section,in Unsigned Short new_section );

};

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ODMG• Programming language (C++) binding

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There is single unified type system across the programming language and the database

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The programming language-specific binding for ODL/OML respects the syntax and semantics of the base programming language into which it is being inserted

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The programming language-specific binding for ODL/OML respects the syntax and semantics of the base programming language into which it is being inserted

The binding is structured as a small set of additions to the base programming language

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Expressions in OML compose freely with expressions from the base programming language and vice versa

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ODMG• C++ binding

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ODMG• C++ binding

Persistent-capable classes

class Professor : public Persistent_Object

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ODMG• C++ binding


class Professor : public Persistent_Object{ public: Ref<Department> dept

inverse Department::professors;

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ODMG• C++ binding


class Professor : public Persistent_Object{ public: Ref<Department> dept

inverse Department::professors;Set<Ref<Student>> advises

inverse Student::advisor;};

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ODMG• C++ binding

Ref-based approach

For each persistence-capable class T, an ancillary class Ref<T> is defined

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ODMG• C++ binding

Ref-based approach

For each persistence-capable class T, an ancillary class Ref<T> is defined

Ref<Professor> profP;Ref<Department> deptRef;profP->grant_tenure();deptRef = profP->dept;

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ODMG• Mapping ODMG Model into C++

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Object type -> C++ class

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Structure -> struct or class

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Collections -> template classes

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Collections -> template classes

template<class T> class Set: public Collection<T>{...};class Ship {...};Set<Ref<Ship>> Cunard_Line;

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subtype/supertype hierarchy ->hierarchy of classes

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operations -> C++ functions

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relationships -> methods that traverse

relationship

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relationships -> methods that traverse

relationship

arrays of objects -> Varray C++ class

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keys -> ?

extents -> ?

name -> ?

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ODMG• C++ ODL

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ODMG• C++ ODL

Attributesclass Student : public Persistent_Object{ String name;

Date birth_date;Phone_Number dorm_phone;

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ODMG• C++ ODL


Date birth_date;Phone_Number dorm_phone;struct{ int PO_box;

String university;String city;String state;String zip_code;

} university_address;

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ODMG• C++ ODL


Date birth_date;Phone_Number dorm_phone;struct{ int PO_box;

String university;String city;String state;String zip_code;

} university_address;List<String> favorite_friends;

};

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ODMG• C++ ODL

Relationshipsclass Department : public Persistent_Object{public:

Set<Ref<Professor>> professorsinverse Professor::dept;

};

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ODMG• C++ ODL

Relationshipsclass Department : public Persistent_Object{public:

Set<Ref<Professor>> professorsinverse Professor::dept;

};

class Professor : public Persistent_Object{

Ref<Department> deptinverse Department::professors;Set<Ref<Student>> adviseesinverse Student::advisor;

};

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ODMG• C++ ODL

Relationshipsclass Student : public Persistent_Object{ public:

Ref<Professor> advisorinverse Professor::advisees;

Set<Ref<Course>> classesinverse Course::students_enrolled;

};

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ODMG• C++ ODL

Relationshipsclass Student : public Persistent_Object{ public:

Ref<Professor> advisorinverse Professor::advisees;

Set<Ref<Course>> classesinverse Course::students_enrolled;

};

class Course : public Persistent_Object{public:

Set<Ref<Student>> students_enrolledinverse Student::classes;

};

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ODMG• C++ ODL

Unidirectional Relationships

struct Responsible{ String dept;

Ref<Employee>e;Date due_date;

};

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ODMG• C++ ODL

Unidirectional Relationships

struct Responsible{ String dept;

Ref<Employee>e;Date due_date;

};

class Order{ public:

Set<Ref<Client>> who;String what;Responsible contact;

};

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ODMG• C++ ODL

Object Creationstatic const Database * const Database::transient_memory;

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ODMG• C++ ODL

Object Creationstatic const Database * const Database::transient_memory;Forms of new operator:(i) void * operator new(

size_t size,const char* typename = 0);

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ODMG• C++ ODL



(ii) void * operator new(size_t size,

constRef<Persistent_Object> &clustering,const char* typename =0);

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ODMG• C++ ODL



(ii) void * operator new(size_t size,

constRef<Persistent_Object> &clustering,const char* typename =0);

(iii) void * operator new(size_t size,Database * database,const char* typename =0);

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ODMG• C++ ODL

Object creationDatabase *yourDB, *myDB;

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ODMG• C++ ODL


Ref<Schedule> temp_sched1 =new Schedule;

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ODMG• C++ ODL



Ref<Professor> prof2 =new( yourDB, "Professor") Professor;

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ODMG• C++ ODL



Ref<Professor> prof2 =new( yourDB, "Professor") Professor;

Ref<Student> student1 =new(myDB) Student;

Ref<Student> student2 = new(student1) Student;

Ref<Student> temp_student =new(Database::transient_memory) Student;

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ODMG• C++ ODL

Object Deletion

Ref<any_Type> obj_ref;// set obj_ref to refer to persistent objectobj_ref.delete_object();

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ODMG• C++ ODL

Object Deletion

Ref<any_Type> obj_ref;// set obj_ref to refer to persistent objectobj_ref.delete_object();

Object Modification

obj_ref->mark_modified();

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ODMG• C++ ODL

Object References

– Object references are instances of Ref<T>

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ODMG• C++ ODL

Object References


– All accesses to persistent objects are made via methods defined on classes Ref, Persistent_Object, Database

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ODMG• C++ ODL

Object References


– All accesses to persistent objects are made via methods defined on classes Ref, Persistent_Object, Database

– The dereference operator -> is used to access members of the persistent object "addressed" by a given object reference

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ODMG• C++ ODL

Attributes

prof->id_number = next_id;

cout << prof->id_number;

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ODMG• C++ ODL

Relationships

1-1class A { Ref<B> inverse B::ra }

class B{ Ref<A> inverse ::rb; }

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ODMG• C++ ODL

Relationships

1-1class A { Ref<B> inverse B::ra }

class B{ Ref<A> inverse ::rb; }

a.rb = &b; //add relationshipa.rb.clear(); // remove relationshipa.rb = &bb; //modify relationship

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ODMG• C++ ODL

Relationships

1:Mclass A{ Set<Ref<B>> sb inverse B::ra; }

class B{ Ref<A> ra inverse A::sb; }

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ODMG• C++ ODL

Relationships

1:Mclass A{ Set<Ref<B>> sb inverse B::ra; }

class B{ Ref<A> ra inverse A::sb; }

a.sb.insert_element(&b); // add relationshipa.sb.remove_element(&b); // remove relationship.

or b.ra.clear();b.ra = &&aa; // modify relationship

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ODMG• C++ ODL

Relationships

M:Nclass A{ Set<Ref<B>> sb inverse B::sa; }

class B{ Set<Ref<A>> sa inverse A:sb; }

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ODMG• C++ ODL

Relationships

M:Nclass A{ Set<Ref<B>> sb inverse B::sa; }

class B{ Set<Ref<A>> sa inverse A:sb; }a.sb.insert_element(&b); // add relationshipa.sb.remove_element(&b); // remove relationship

or b.sa.remove_element(&a);a.sb.replace_element_at(&bb, 3); // modify relationship

Documents

1 ODMG. 2 Object Database Management Group (ODMG) ODMG has been formed in late 1991 by: ObjectDesign,…