Object Identity:

Any object has 2 properties i.e. state & behaviour hence, it’s similar to the program variable but object has complex structure.

• There are two types of object :-

  1.) Transient object 2.) Persistent object

  1.) Transient object: - These objects exist during the execution but destroy ones the program terminates.

  2.) Persistent object: - These objects persist & store into database even if program terminate. Whenever any object created DBMS assigns unique identifier called as object identity & its abbreviated as OID.

OID is used for two purposes.

• To identity each objects uniquely.
• Make reference to another object.
• Properties of OID
• Its unique
• Its system generated
• Its invisible to the user
• It’s not possible t perform operation on OID
• It’s in mutable i.e. once its generated
• It cannot be regenerated
• It has along integer values
• Object structure

Every object has internal structure that can be specified by using 6 types of type constructor (AST LAM)…

1. ATDM: - Internal structure of object consists of automatic values that may be of type integer float, character, string, data etc.
2. SET:- Internal structure of object, consist of collection of OID’s of other objects that may be constructed from different type constructor its denoted by {i1 , i2 , i3 , …}
3. Tuples:- Internal structure of object, consist of collection of OID’s other objects that may be constructed from different type constructor its denoted by {a1 : i1 ; a2 : i2 ; a3 : i3, …} where a1 , a2 , a3 , … be the attributers & i1 , i2 , i3 be OID’s
4. List :- Its similar to the set but it’s an ordered collection its denoted by { i1 , i2 , i3 , …}
5. ARRAY: - It’s similar to list but it has limitations I.e. it’s of fixed size.
6. MULTISET or bag: - It’s similar to the set but it may contain duplicate. Any object structure is represented

By triplet i.e. {I, C, V}

I = Object identifier.

E = type constructer.

V = value.

For e.g.:- Let us consider the following relation.

Location:-

For above 2 relations object structure can be created as follows:-

01 = <i1, atom,="" 5="">

02 = <i2, atom,="" “research="">”

03 = <i3, atom,="" “l1”&gt;<="" p="">

04 = <i4, atom,="" “l2”&gt;<="" p="">

05 = <i5, set,="" <i3,="" i4="" &gt;<="" p="">

06 = <i6, tuple="" ;&lt;="" dno;="" i="" 1,="" d="" name="" i2,="" coc="">

• Type constructor

  It’s used to define the data structure for object oriented, DB there are six types of type constructor. (Refer objects structure)

  Let us consider employee & department relation.

  Type constructor can be created as follows:-

     Define type employees
     Type   (id: integer;
      Name: string, 
      Gender: string,
      DOB: date,
      Address: string,
      Salary: Float
      Manager: Employee,
      D no: Department.)
      End;
  
  
     Define type name 
     Type (fname
               Mname
               Dname)
               End;
  
       Define type address 
         Type (apt no:              
                   Area:
                   City:
                   Pin code:
                    End;   )
  
      Define type department 
      Type (dno: integer
                 Dname: string
                Location: set (string), manager
                                    Employees)
                 End;