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Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
Newreport db
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Newreport db

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  • 1. INTRODUCTION There are some instances when a primary key doesn’t exist in the real world or when the existingnatural key might not be a suitable primary key.
  • 2. SURROGATE KEY:Is a primary key created bythe database designer tosimplify the identification ofentity instances.
  • 3. ADVANTAGESince it has no intrinsic meaning,values for it can be generated bythe DBMS to ensure that uniquevalues are always provided.
  • 4. TABLE 5.4 DATE TIME_START TIME_END ROOM EVENT_NAME PARTY_OF6/17/2010 11:00AM 2:00PM Allure Burton 60 Wedding6/17/2010 11:00AM 2:00PM Bonanza Adams Office 126/17/2010 3:00PM 5:30PM Allure Smith Family 156/17/2010 3:30PM 5:30PM Bonanza Adam’s Office 126/18/2010 1:00PM 3:00PM Bonanza Boy Scouts 336/18/2010 11:00AM 2:00PM Allure March of 25 Dines6/18/2010 11:00AM 12:30PM Bonanza Smith Family 12
  • 5.  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)
  • 6. DATE TIME_ TIME ROOM EVENT_ PART START _EN NAME Y_OF What primary key would you D suggest? In this case , there is no6/17 11:00 2:00 Allure Burton 60 simple natural key that could be /10 AM PM Wedding used as a primary key in the6/17/ 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 might6/17/ 3:00 5:30 Allure Smith 15 suggest one of these options. 10 PM PM Family6/17/ 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 Dines6/18/ 11:00 12:3 Bonanza Smith 12 10 AM 0PM Family
  • 7. DAT TIME_ TIME ROOM EVENT_ PART E START _EN NAME Y_OF Assume you select the D composite primary key (DATE, TIME_START,ROOM) for the6/17 11:00 2:00P Allure Burton 60 EVENT entity. Next ,you/10 AM M Wedding determine that one EVENT may6/17 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 same6/17 3:00 5:30P Allure Smith 15 RESOURCE may be use for/10 PM M Family many EVENTS. The RESOURCE entity would be represented by6/17 3:30 5:30P Bonan Adam’s 12 the ff. attributes:/10 PM M za Office6/18 1:00 3:00P Bonan Boy 33 RESOURCE (RSC_ID,/10 PM M za Scouts RSC_DESCRIPTION,RSC_T6/18 11:00 2:00P Allure March of 25 YPE, RSC_QTY,RSC_PRICE)/10 AM M Dines6/18 11:00 12:30 Bonan Smith 12/10 AM PM za Family
  • 8. 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 represented6/17 11:00 2:00P Allure Burton 60 via the EVNTRSC composite entity/10 AM M Wedding with a composite primary key as6/17 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 another6/18 1:00 3:00P Bonan Boy 33 existence dependent entity? At/10 PM M za Scouts this point, you can see that the6/18 11:00 2:00P Allure March of 25 composite primary key could/10 AM M Dines make the implementation of the database and program coding6/18 11:00 12:30 Bonan Smith 12 unnecessarily complex./10 AM PM za Family
  • 9. Surrogate primary keys are accepted practice in todays complex data environments.
  • 10. 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.
  • 11. 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.
  • 12. PREPARED BY: ROSELYN P. CEAALLYSA JANE CATALLA BLIS -III

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