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Catalla & cea
INTRODUCTION

 There are some instances when a
  primary key doesn’t exist in the
  real world or when the existing
natural key might not be a suitable
           primary key.
SURROGATE KEY:

Is a primary key created by
the database designer to
simplify the identification of
entity instances.
Catalla & cea
ADVANTAGE

Since it has no intrinsic meaning,
values for it can be generated by
the DBMS to ensure that unique
values are always provided.
Catalla & cea
TABLE 5.4


  DATE       TIME_START   TIME_END   ROOM      EVENT_NAME      PARTY_OF

6/17/2010     11:00AM      2:00PM    Allure      Burton           60
                                                 Wedding
6/17/2010     11:00AM      2:00PM    Bonanza   Adams Office       12

6/17/2010     3:00PM       5:30PM     Allure   Smith Family       15

6/17/2010     3:30PM       5:30PM    Bonanza   Adam’s Office      12

6/18/2010     1:00PM       3:00PM    Bonanza    Boy Scouts        33

6/18/2010     11:00AM      2:00PM     Allure     March of         25
                                                  Dines
6/18/2010     11:00AM     12:30PM    Bonanza   Smith Family       12
 Given the data shown in table 5.4 you would
          model the EVENT entity as:

EVENT(DATE, TIME_START, TIME_END,ROOM
        ,EVENT_NAME,PARTY_OF)
DATE TIME_ TIME        ROOM      EVENT_     PART
     START _EN                    NAME      Y_OF   What primary key would you
             D                                     suggest? In this case , there is no
6/17 11:00 2:00        Allure    Burton      60    simple natural key that could be
 /10  AM    PM                   Wedding
                                                   used as a primary key in the
6/17/   11:00   2:00   Bonanza   Adams       12    model. Based on the primary key
 10      AM     PM               Office            concepts you learned about in
                                                   previous chapters, you might
6/17/   3:00    5:30    Allure    Smith      15    suggest one of these options.
 10     PM      PM                Family

6/17/   3:30    5:30   Bonanza   Adam’s      12
 10     PM      PM                Office

                                                       (DATE, TIME_START, ROOM)
6/18/   1:00    3:00   Bonanza     Boy       33                    Or
 10     PM      PM                Scouts                (DATE, TIME_END, ROOM)
6/18/   11:00   2:00    Allure   March of    25
 10      AM     PM                Dines
6/18/   11:00   12:3 Bonanza      Smith      12
 10      AM     0PM               Family
DAT TIME_      TIME_   ROO      EVENT_     PART
 E  START       END     M        NAME      Y_OF        Assume you select the
                                                  composite primary key (DATE,
                                                  TIME_START,ROOM) for the
6/17   11:00   2:00P   Allure   Burton      60    EVENT entity. Next ,you
/10     AM       M              Wedding
                                                  determine that one EVENT may
6/17   11:00   2:00P   Bonan    Adams       12    use many RESOURCES such as
/10     AM       M       za     Office            tables, projectors, pc and
                                                  stands, and that the same
6/17   3:00    5:30P   Allure    Smith      15    RESOURCE may be use for
/10    PM        M               Family           many EVENTS. The RESOURCE
                                                  entity would be represented by
6/17   3:30    5:30P   Bonan    Adam’s      12    the ff. attributes:
/10    PM        M       za      Office

6/18   1:00    3:00P   Bonan      Boy       33    RESOURCE (RSC_ID,
/10    PM        M       za      Scouts           RSC_DESCRIPTION,RSC_T
6/18   11:00   2:00P   Allure   March of    25    YPE, RSC_QTY,RSC_PRICE)
/10     AM       M               Dines
6/18   11:00   12:30   Bonan     Smith      12
/10     AM      PM       za      Family
DATE TIME_ TIME        ROOM     EVENT      PART
     START _EN                  _NAME      Y_OF   Given the business rules, the M:N
             D                                    relationship between RESOURCE
                                                  and EVENT would be represented
6/17   11:00   2:00P   Allure   Burton      60
                                                  via the EVNTRSC composite entity
/10     AM       M              Wedding
                                                  with a composite primary key as
6/17   11:00   2:00P   Bonan    Adams       12    follows:
/10     AM       M       za     Office
                                                    EVNTRSC (DATE, TIME _START,
6/17   3:00    5:30P   Allure    Smith      15      ROOM, RSC_ID, QTY _USED
/10    PM        M               Family
                                                   You now have a lengthy four-
6/17   3:30    5:30P   Bonan    Adam’s      12     attribute composite primary key.
/10    PM        M       za      Office            What would happen if the
                                                   EVNTRSC entity’s primary key
                                                   were inherited by another
6/18   1:00    3:00P   Bonan      Boy       33     existence dependent entity? At
/10    PM        M       za      Scouts            this point, you can see that the
6/18   11:00   2:00P   Allure   March of    25     composite primary key could
/10     AM       M               Dines             make the implementation of the
                                                   database and program coding
6/18   11:00   12:30   Bonan     Smith      12
                                                   unnecessarily complex.
/10     AM      PM       za      Family
Surrogate primary keys are accepted
   practice in today's complex data
            environments.
They are especially helpful when there
  is no natural key, when the selected
 candidate key has embedded semantic
     contents or when the selected
       candidate key is too long or
             cumbersome.
However , there is a trade-off; if you use
  a surrogate key, you must ensure that
     the candidate key of the entity in
 question performs properly through the
  use of “unique index” and “not null”
               constraints.
PREPARED BY:




   ROSELYN P. CEA
ALLYSA JANE CATALLA
      BLIS -III

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Catalla & cea

  • 2. INTRODUCTION There are some instances when a primary key doesn’t exist in the real world or when the existing natural key might not be a suitable primary key.
  • 3. SURROGATE KEY: Is a primary key created by the database designer to simplify the identification of entity instances.
  • 5. ADVANTAGE Since it has no intrinsic meaning, values for it can be generated by the DBMS to ensure that unique values are always provided.
  • 7. TABLE 5.4 DATE TIME_START TIME_END ROOM EVENT_NAME PARTY_OF 6/17/2010 11:00AM 2:00PM Allure Burton 60 Wedding 6/17/2010 11:00AM 2:00PM Bonanza Adams Office 12 6/17/2010 3:00PM 5:30PM Allure Smith Family 15 6/17/2010 3:30PM 5:30PM Bonanza Adam’s Office 12 6/18/2010 1:00PM 3:00PM Bonanza Boy Scouts 33 6/18/2010 11:00AM 2:00PM Allure March of 25 Dines 6/18/2010 11:00AM 12:30PM Bonanza Smith Family 12
  • 8.  Given the data shown in table 5.4 you would model the EVENT entity as: EVENT(DATE, TIME_START, TIME_END,ROOM ,EVENT_NAME,PARTY_OF)
  • 9. DATE TIME_ TIME ROOM EVENT_ PART START _EN NAME Y_OF What primary key would you D suggest? In this case , there is no 6/17 11:00 2:00 Allure Burton 60 simple natural key that could be /10 AM PM Wedding used as a primary key in the 6/17/ 11:00 2:00 Bonanza Adams 12 model. Based on the primary key 10 AM PM Office concepts you learned about in previous chapters, you might 6/17/ 3:00 5:30 Allure Smith 15 suggest one of these options. 10 PM PM Family 6/17/ 3:30 5:30 Bonanza Adam’s 12 10 PM PM Office (DATE, TIME_START, ROOM) 6/18/ 1:00 3:00 Bonanza Boy 33 Or 10 PM PM Scouts (DATE, TIME_END, ROOM) 6/18/ 11:00 2:00 Allure March of 25 10 AM PM Dines 6/18/ 11:00 12:3 Bonanza Smith 12 10 AM 0PM Family
  • 10. DAT TIME_ TIME_ ROO EVENT_ PART E START END M NAME Y_OF Assume you select the composite primary key (DATE, TIME_START,ROOM) for the 6/17 11:00 2:00P Allure Burton 60 EVENT entity. Next ,you /10 AM M Wedding determine that one EVENT may 6/17 11:00 2:00P Bonan Adams 12 use many RESOURCES such as /10 AM M za Office tables, projectors, pc and stands, and that the same 6/17 3:00 5:30P Allure Smith 15 RESOURCE may be use for /10 PM M Family many EVENTS. The RESOURCE entity would be represented by 6/17 3:30 5:30P Bonan Adam’s 12 the ff. attributes: /10 PM M za Office 6/18 1:00 3:00P Bonan Boy 33 RESOURCE (RSC_ID, /10 PM M za Scouts RSC_DESCRIPTION,RSC_T 6/18 11:00 2:00P Allure March of 25 YPE, RSC_QTY,RSC_PRICE) /10 AM M Dines 6/18 11:00 12:30 Bonan Smith 12 /10 AM PM za Family
  • 11. DATE TIME_ TIME ROOM EVENT PART START _EN _NAME Y_OF Given the business rules, the M:N D relationship between RESOURCE and EVENT would be represented 6/17 11:00 2:00P Allure Burton 60 via the EVNTRSC composite entity /10 AM M Wedding with a composite primary key as 6/17 11:00 2:00P Bonan Adams 12 follows: /10 AM M za Office EVNTRSC (DATE, TIME _START, 6/17 3:00 5:30P Allure Smith 15 ROOM, RSC_ID, QTY _USED /10 PM M Family You now have a lengthy four- 6/17 3:30 5:30P Bonan Adam’s 12 attribute composite primary key. /10 PM M za Office What would happen if the EVNTRSC entity’s primary key were inherited by another 6/18 1:00 3:00P Bonan Boy 33 existence dependent entity? At /10 PM M za Scouts this point, you can see that the 6/18 11:00 2:00P Allure March of 25 composite primary key could /10 AM M Dines make the implementation of the database and program coding 6/18 11:00 12:30 Bonan Smith 12 unnecessarily complex. /10 AM PM za Family
  • 12. Surrogate primary keys are accepted practice in today's complex data environments.
  • 13. They are especially helpful when there is no natural key, when the selected candidate key has embedded semantic contents or when the selected candidate key is too long or cumbersome.
  • 14. However , there is a trade-off; if you use a surrogate key, you must ensure that the candidate key of the entity in question performs properly through the use of “unique index” and “not null” constraints.
  • 15. PREPARED BY: ROSELYN P. CEA ALLYSA JANE CATALLA BLIS -III