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Explain with suitable e.g. object identity, object structure & type constructors in OODBs.
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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.

Dno Dname - - -
5 Research - - -

Location:-

Dno Dname
5 4
5 12

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;
    
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