Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zImplementation
Appendix C #z
The University Lab: Conceptual Design, Verification,
#z #z #z #z #z
Logical Design, and Implementation
#z #z #z #z
Discussion Focus #z
How #zis #za #zdatabase #zdesign #zverified, #zand #zwhy #zis #zsuch #zverification #znecessary?
Use #zour #zdetailed #zanswer #zto #zquestion #z1 #zto #zfocus #zclass #zdiscussion #zon #zdatabase #zdesign
#zverification. # z Stress #zthat #zthe #zverification #zprocess #zuses #zthe #zinitial #zER #zmodel #zas #za #zcommunication
#ztool.
The #zdesigner #zmay #zbegin #zthe #zverification #zprocess #zby #zdescribing #zthe #zorganization's #zoperations #zto
#zits #zend #zusers, #zbasing #zthe #zdetailed #zdescription #zon #zthe #zinitial #zER #zmodel. # z Next, #zexplain #zhow #zthe
#zoperations #zwill #zbe #zsupported #zby #zthe #zdatabase #zdesign. #zStress #zthat #zthe #zdesign #zmust #zsupport #zthe
#zend-user #zapplication #zviews, #zoutputs, #zand #zinputs. #zPoints #zto #zbe #zaddressed #zinclude #zsuch #zquestions
#zas:
• Is #zthe #zdescription #zaccurate? #zIf #znot, #zwhat #zaspects #zof #zthe #zdescription #zmust #zbe #zcorrected?
• Does # z the # z model # z support # z the # z end-user # z requirements? # z If # z not, # z what # z aspects # z of
# z the # z end-user #zrequirements #zhave #znot #zbeen #zaddressed #zor #zhave #zbeen #zaddressed
#zinadequately?
Keep #zin #zmind #zthat #zeven #za #zmodel #zthat #zperfectly #zaddresses #zall #zinitially #zdetermined #zend #zuser
#zrequirements # z is #zlikely #zto #zneed #zadjustments #zas #zthose #zend #zusers #zbegin #zto #zunderstand #zthe
#zramifications #zof #zthe #zdatabase #zdesign's #zcapabilities. #zIn #zmany #zcases, #zthe #zend #zusers #zmay #zlearn
#zwhat #zthe #zorganization's #zprocesses #zand #zprocedures #zactually #zare, #zthus #zleading #zto #znew
#zrequirements #zand #zthe #zperception #zof #znew #zopportunities. #zThe #zdatabase #zdesigner #zmust #zkeep #zsuch
#zlikely #zdevelopments #zin #zmind, #zespecially #zif #z(s)he #zworks #zas #za #zdatabase #zdesign #zconsultant.
#z(Anticipation #zof #zsuch #zdevelopments #zmust #zbe #zfactored #zinto #zthe #zcontract #znegotiations #zfor
#zconsulting #zfees.)
1
, Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zImplementation
Discuss #zthe #zrole #zof #zthe #zsystem #zmodules.
The use of system modules can hardly be overemphasized in a database design environment. Stress
these module characteristics and features:
• Modules represent subsets of the database model: Smaller "pieces" are more easily
understood.
• Modules are self-contained and accomplish a specific system function; if such a system
function must be modified, other functions remain unaffected.
• Modules fit into a modular database design, which is more easily modified and adapted to
new circumstances. Because modification efforts are focused on a database subset,
productivity of both designers and application developers is likely to be enhanced.
Module interfaces must be clear if the modules are expected to work well within the overall system.
Answers to Review Questions
#z #z #z
1. Why #zmust #za #zconceptual #zmodel #zbe #zverified? #zWhat #zsteps #zare #zinvolved #zin #zthe #zverification #zprocess?
The #zverification #zof #za #zconceptual #zmodel #zis #zcrucial #zto #za #zsuccessful #zdatabase #zdesign. #zThe
#zverification #zprocess #zallows #zthe #zdesigner #zto #zcheck #zthe #zaccuracy #zof #zthe #zdatabase #zdesign #zby:
• Re-examining #zdata #zand #zdata #ztransformations.
• Enabling #zthe #zdesigner #zto #zevaluate #zthe #zdesign #zefficiency #zrelative #zto #zthe #zend
#zuser's #zand #zsystem's #zdesign #zgoals.
Keep #zin #zmind #zthat, #zto #za #zlarge #zextent, #zthe #zbest #zdesign #zis #zthe #zone #zthat #zserves #zthe #zend-user
#zrequirements #zbest. #zFor #zexample, #za #zdesign #zthat #zworks #zwell #zfor #za #zmanufacturing #zfirm #zmay
#znot #zfit #zthe #zneeds #zof #za #zmarketing #zresearch #zfirm, #zand #zvice #zversa.
The #zverification #zprocess #zhelps #zthe #zdesigner #zto #zavoid #zimplementation #zproblems #zlater #zby:
• Validating #zthe #zmodel's #zentities. #z(Remember #zthe #zminimal #zdata #zrule.)
• Confirming #zentity #zrelationships #zand #zeliminating #zduplicate, #zunnecessary, #zor
#zimproperly #zdefined #zrelationships.
• Eliminating #zdata #zredundancies.
• Improving #zthe #zmodel's #zsemantic #zprecision #zto #zbetter #zrepresent #zreal-world #zoperations.
• Confirming #zthat #zall #zuser #zrequirements #z(processing, #zperformance, #zor #zsecurity) #zare #zmet.
Verification #zis #za #zcontinuous #zactivity #zin #zany #zdatabase #zdesign. #zThe #zdatabase #zdesign #zprocess #zis
#zevolutionary #zin #znature: #zIt #zrequires #zthe #zcontinuous #zevaluation #zof #zthe #zdeveloping #zmodel #zby
#zexamining #zthe #zeffect #zof #zadding #znew #zentities #zand #zby #zconfirming #zthat #zany #zdesign #zchanges
2
, Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zenhance #zthe #zmodel's #zaccuracy. #zImplementation
The #zverification #zprocess #zrequires #zthe #zfollowing #zsteps:
1. Identify #zthe #zdatabase's #zcentral #zentity.
The # z central # z entity # z is # z the # z most # z important # z entity # z in # z our # z database, # z and
# z most # z of # z the # z other #zentities #zdepend #zon #zit.
2. Identify #zand #zdefine #zeach #zmodule #zand #zits #zcomponents.
The # z designer # z divides # z the # z database # z model # z into # z smaller # z sets # z that # z reflect # z the
# z data # z needs # z of #zparticular #zsystems #zmodules #zsuch #zas #zinventory, #zorders, #zpayroll, #zetc.
3. Identify #zand #zdefine #zeach #zof #zthe #zmodule's #zprocesses.
Specifically, #zthis #z step #z requires #z the #z identification #z and #z definition #zof #z the #z database # z transactions
that #zrepresent #zthe #zmodule's #zreal-world #zoperations.
4. Verify #zeach #zof #zthe #ztransactions #zagainst #zthe #zdatabase.
2. What #zsteps #zmust #zbe #zcompleted #zbefore #zthe #zdatabase #zdesign #zis #zfully #zimplemented? #z(Make
#zsure #zthat #zyou #zlist #zthe #zsteps #zin #zthe #zcorrect #zsequence #zand #zdiscuss #zeach #zstep #zbriefly.)
The #zDBLC, #zdiscussed #zin #zdetail #zin #zChapter #z9, #z“Database #zDesign,” #zconstitutes #za #zdatabase's
#zhistory, #ztracing #zit #zfrom #zits #zconceptual #zdesign #zto #zits #zimplementation #zand #zoperation. #zWe
#zhighly #zrecommend #zthat #zthe #zdatabase #zdesigner #zfollow #zthe #zDBLC's #zsteps #zcarefully #zin #zorder #zto
#zensure #zthat #zthe #zdatabase #zwill #zproperly #zmeet #zall #zuser #zand #zsystem #zrequirements.
Before #za #zdatabase #zcan #zbe #zsuccessfully #zimplemented, #zthe #zfollowing #zsteps #zmust #zbe #zcompleted:
1. Define #zthe #zconceptual #zmodel's #zcomponents: #zentities, #zattributes, #zdomains, #zand #zrelationships.
2. Normalize #zthe #zdatabase #zto #zensure #zthat #zall #ztransitive #zdependencies #zare #zeliminated
#zand #zthat #zeach #zentity's #zattributes #zare #zsolely #zdependent #zon #zits #zkey #zattribute(s).
3. Verify #zthe #zconceptual #zmodel #zto #zensure #zthat #zthe #zproposed #zdatabase #zwill #zmeet #zthe
#zsystem's # z transaction #zrequirements #zand #zthat #zthe #zend-user #zand #zsystems #zrequirements
#zwill #zbe #zmet.
3
, Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zImplementation
The # z verification # z process # z will # z probably # z delete # z and/or # z create
# z entities, # z attributes, # z and #zrelationships. #zIt #zmay #zalso #zrefine #zexisting #zentities,
#zattributes, #zand #zrelationships.
4. Create #zthe #zlogical #zdesign #zwhich #zrequires #zthe #zdefinition #zof #zthe #ztable #zstructures, #zusing
#za # z specific #zDBMS #z(relational, #znetwork #zor #zhierarchical). #zLogical #zdesign #zalso #zincludes,
#zif #znecessary, #zappropriate #zindexes #zand #zviews.
5. Create #zthe #zphysical #zdesign #zto #zdefine #zaccess #zpaths, #zincluding #zspace #zallocation, #zstorage
#zgroup #zcreation, #ztable #zspaces, #zand #zany #zother #zphysical #zstorage #zcharacteristic #zthat #zis
#zdependent #zon # z the #zhardware #zand #zsoftware #zto #zbe #zused #zin #zthe #zsystem's
#zimplementation.
6. Implement #zthe #zdesign. # z Somehow, #zthis #zlast #zstep #zseems #zto #zsuffer #zfrom #zplanning
#zneglect, #zto # z the #zdetriment #zof #zthe #zsystem's #zoperation. #zImplementation, #zoperation,
#zand #zmaintenance # z plans #zmust #z(at #zleast) #zinclude #zcareful #zdefinition #zand #zdescription #zof
#zthe #zactivities #zrequired #zto #zimplement #zthe #zdatabase #zdesign:
• loading #zand #zconversion
• definition #zof #zdatabase #zstandards
• system #zand #zprocedures #zdocumentation: #zsecurity, #zbackup, #zand #zrecovery
• operational #zprocedures #zto #zbe #zfollowed #zby #zusers
• a #zdetailed #ztraining #zplan
• identification #zof #zresponsibilities #zfor #zoperation #zand #zmaintenance.
3. What # z major # z factors # z should # z be # z addressed # z when # z database # z system # z performance
# z is # z evaluated? #zDiscuss #zeach #zfactor #zbriefly.
Database #zsystems #zperformance #zrefers #zto #zthe #zsystem's #zability #zto #zretrieve #zinformation #zwithin #za
#zreasonable #zamount #zof #ztime #zand #zat #za #zreasonable #zcost. #zKeeping #zin #zmind #zthat #z"reasonable"
#zmeans #zdifferent #zthings #zto #zdifferent #zpeople, #zwe #zmust #zaddress #zat #zleast #zthese #zimportant
#zperformance #zfactors:
• Concurrent #zusers
For # z any # z given # z system, # z the # z more # z users # z connected # z to # z the # z system, # z the
# z longer # z the # z data #zretrieval #ztime.
• Resource #zlimits
The #zfewer #zresources #zthat #zare #zavailable #zto #zthe #zuser, #zthe #zlonger #zthe #zaccess #zqueues #zwill #zbe.
• Communication #zspeeds
Lower #zcommunication #zspeeds #zmean #zlonger #zresponse #ztimes.
• Query #zresponse #ztime
Queries #zmust #zbe #ztuned #zto #zprovide #zoptimum #zquery #zresponse #ztime. #z(See #zAppendix #zC,
#z“Database #zPerformance #zTuning.”) #zLack #zof #zquery #zresponse #ztuning #zmeans #zslow
#zresponse # z times. #zDepending #zon #zhow #zgood #zthe #zdesign #zand #zthe #zprogram #zcode #zare,
#zthe #zquery #zresponse #ztime #zcan #zvary #zfrom #zminutes #zto #zhours #zfor #zthe #zsame #zquery.
4
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zImplementation
Appendix C #z
The University Lab: Conceptual Design, Verification,
#z #z #z #z #z
Logical Design, and Implementation
#z #z #z #z
Discussion Focus #z
How #zis #za #zdatabase #zdesign #zverified, #zand #zwhy #zis #zsuch #zverification #znecessary?
Use #zour #zdetailed #zanswer #zto #zquestion #z1 #zto #zfocus #zclass #zdiscussion #zon #zdatabase #zdesign
#zverification. # z Stress #zthat #zthe #zverification #zprocess #zuses #zthe #zinitial #zER #zmodel #zas #za #zcommunication
#ztool.
The #zdesigner #zmay #zbegin #zthe #zverification #zprocess #zby #zdescribing #zthe #zorganization's #zoperations #zto
#zits #zend #zusers, #zbasing #zthe #zdetailed #zdescription #zon #zthe #zinitial #zER #zmodel. # z Next, #zexplain #zhow #zthe
#zoperations #zwill #zbe #zsupported #zby #zthe #zdatabase #zdesign. #zStress #zthat #zthe #zdesign #zmust #zsupport #zthe
#zend-user #zapplication #zviews, #zoutputs, #zand #zinputs. #zPoints #zto #zbe #zaddressed #zinclude #zsuch #zquestions
#zas:
• Is #zthe #zdescription #zaccurate? #zIf #znot, #zwhat #zaspects #zof #zthe #zdescription #zmust #zbe #zcorrected?
• Does # z the # z model # z support # z the # z end-user # z requirements? # z If # z not, # z what # z aspects # z of
# z the # z end-user #zrequirements #zhave #znot #zbeen #zaddressed #zor #zhave #zbeen #zaddressed
#zinadequately?
Keep #zin #zmind #zthat #zeven #za #zmodel #zthat #zperfectly #zaddresses #zall #zinitially #zdetermined #zend #zuser
#zrequirements # z is #zlikely #zto #zneed #zadjustments #zas #zthose #zend #zusers #zbegin #zto #zunderstand #zthe
#zramifications #zof #zthe #zdatabase #zdesign's #zcapabilities. #zIn #zmany #zcases, #zthe #zend #zusers #zmay #zlearn
#zwhat #zthe #zorganization's #zprocesses #zand #zprocedures #zactually #zare, #zthus #zleading #zto #znew
#zrequirements #zand #zthe #zperception #zof #znew #zopportunities. #zThe #zdatabase #zdesigner #zmust #zkeep #zsuch
#zlikely #zdevelopments #zin #zmind, #zespecially #zif #z(s)he #zworks #zas #za #zdatabase #zdesign #zconsultant.
#z(Anticipation #zof #zsuch #zdevelopments #zmust #zbe #zfactored #zinto #zthe #zcontract #znegotiations #zfor
#zconsulting #zfees.)
1
, Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zImplementation
Discuss #zthe #zrole #zof #zthe #zsystem #zmodules.
The use of system modules can hardly be overemphasized in a database design environment. Stress
these module characteristics and features:
• Modules represent subsets of the database model: Smaller "pieces" are more easily
understood.
• Modules are self-contained and accomplish a specific system function; if such a system
function must be modified, other functions remain unaffected.
• Modules fit into a modular database design, which is more easily modified and adapted to
new circumstances. Because modification efforts are focused on a database subset,
productivity of both designers and application developers is likely to be enhanced.
Module interfaces must be clear if the modules are expected to work well within the overall system.
Answers to Review Questions
#z #z #z
1. Why #zmust #za #zconceptual #zmodel #zbe #zverified? #zWhat #zsteps #zare #zinvolved #zin #zthe #zverification #zprocess?
The #zverification #zof #za #zconceptual #zmodel #zis #zcrucial #zto #za #zsuccessful #zdatabase #zdesign. #zThe
#zverification #zprocess #zallows #zthe #zdesigner #zto #zcheck #zthe #zaccuracy #zof #zthe #zdatabase #zdesign #zby:
• Re-examining #zdata #zand #zdata #ztransformations.
• Enabling #zthe #zdesigner #zto #zevaluate #zthe #zdesign #zefficiency #zrelative #zto #zthe #zend
#zuser's #zand #zsystem's #zdesign #zgoals.
Keep #zin #zmind #zthat, #zto #za #zlarge #zextent, #zthe #zbest #zdesign #zis #zthe #zone #zthat #zserves #zthe #zend-user
#zrequirements #zbest. #zFor #zexample, #za #zdesign #zthat #zworks #zwell #zfor #za #zmanufacturing #zfirm #zmay
#znot #zfit #zthe #zneeds #zof #za #zmarketing #zresearch #zfirm, #zand #zvice #zversa.
The #zverification #zprocess #zhelps #zthe #zdesigner #zto #zavoid #zimplementation #zproblems #zlater #zby:
• Validating #zthe #zmodel's #zentities. #z(Remember #zthe #zminimal #zdata #zrule.)
• Confirming #zentity #zrelationships #zand #zeliminating #zduplicate, #zunnecessary, #zor
#zimproperly #zdefined #zrelationships.
• Eliminating #zdata #zredundancies.
• Improving #zthe #zmodel's #zsemantic #zprecision #zto #zbetter #zrepresent #zreal-world #zoperations.
• Confirming #zthat #zall #zuser #zrequirements #z(processing, #zperformance, #zor #zsecurity) #zare #zmet.
Verification #zis #za #zcontinuous #zactivity #zin #zany #zdatabase #zdesign. #zThe #zdatabase #zdesign #zprocess #zis
#zevolutionary #zin #znature: #zIt #zrequires #zthe #zcontinuous #zevaluation #zof #zthe #zdeveloping #zmodel #zby
#zexamining #zthe #zeffect #zof #zadding #znew #zentities #zand #zby #zconfirming #zthat #zany #zdesign #zchanges
2
, Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zenhance #zthe #zmodel's #zaccuracy. #zImplementation
The #zverification #zprocess #zrequires #zthe #zfollowing #zsteps:
1. Identify #zthe #zdatabase's #zcentral #zentity.
The # z central # z entity # z is # z the # z most # z important # z entity # z in # z our # z database, # z and
# z most # z of # z the # z other #zentities #zdepend #zon #zit.
2. Identify #zand #zdefine #zeach #zmodule #zand #zits #zcomponents.
The # z designer # z divides # z the # z database # z model # z into # z smaller # z sets # z that # z reflect # z the
# z data # z needs # z of #zparticular #zsystems #zmodules #zsuch #zas #zinventory, #zorders, #zpayroll, #zetc.
3. Identify #zand #zdefine #zeach #zof #zthe #zmodule's #zprocesses.
Specifically, #zthis #z step #z requires #z the #z identification #z and #z definition #zof #z the #z database # z transactions
that #zrepresent #zthe #zmodule's #zreal-world #zoperations.
4. Verify #zeach #zof #zthe #ztransactions #zagainst #zthe #zdatabase.
2. What #zsteps #zmust #zbe #zcompleted #zbefore #zthe #zdatabase #zdesign #zis #zfully #zimplemented? #z(Make
#zsure #zthat #zyou #zlist #zthe #zsteps #zin #zthe #zcorrect #zsequence #zand #zdiscuss #zeach #zstep #zbriefly.)
The #zDBLC, #zdiscussed #zin #zdetail #zin #zChapter #z9, #z“Database #zDesign,” #zconstitutes #za #zdatabase's
#zhistory, #ztracing #zit #zfrom #zits #zconceptual #zdesign #zto #zits #zimplementation #zand #zoperation. #zWe
#zhighly #zrecommend #zthat #zthe #zdatabase #zdesigner #zfollow #zthe #zDBLC's #zsteps #zcarefully #zin #zorder #zto
#zensure #zthat #zthe #zdatabase #zwill #zproperly #zmeet #zall #zuser #zand #zsystem #zrequirements.
Before #za #zdatabase #zcan #zbe #zsuccessfully #zimplemented, #zthe #zfollowing #zsteps #zmust #zbe #zcompleted:
1. Define #zthe #zconceptual #zmodel's #zcomponents: #zentities, #zattributes, #zdomains, #zand #zrelationships.
2. Normalize #zthe #zdatabase #zto #zensure #zthat #zall #ztransitive #zdependencies #zare #zeliminated
#zand #zthat #zeach #zentity's #zattributes #zare #zsolely #zdependent #zon #zits #zkey #zattribute(s).
3. Verify #zthe #zconceptual #zmodel #zto #zensure #zthat #zthe #zproposed #zdatabase #zwill #zmeet #zthe
#zsystem's # z transaction #zrequirements #zand #zthat #zthe #zend-user #zand #zsystems #zrequirements
#zwill #zbe #zmet.
3
, Appendix #zC #zThe #zUniversity #zLab:
Conceptual #zDesign #zVerification, #zLogical #zDesign, #zand
#zImplementation
The # z verification # z process # z will # z probably # z delete # z and/or # z create
# z entities, # z attributes, # z and #zrelationships. #zIt #zmay #zalso #zrefine #zexisting #zentities,
#zattributes, #zand #zrelationships.
4. Create #zthe #zlogical #zdesign #zwhich #zrequires #zthe #zdefinition #zof #zthe #ztable #zstructures, #zusing
#za # z specific #zDBMS #z(relational, #znetwork #zor #zhierarchical). #zLogical #zdesign #zalso #zincludes,
#zif #znecessary, #zappropriate #zindexes #zand #zviews.
5. Create #zthe #zphysical #zdesign #zto #zdefine #zaccess #zpaths, #zincluding #zspace #zallocation, #zstorage
#zgroup #zcreation, #ztable #zspaces, #zand #zany #zother #zphysical #zstorage #zcharacteristic #zthat #zis
#zdependent #zon # z the #zhardware #zand #zsoftware #zto #zbe #zused #zin #zthe #zsystem's
#zimplementation.
6. Implement #zthe #zdesign. # z Somehow, #zthis #zlast #zstep #zseems #zto #zsuffer #zfrom #zplanning
#zneglect, #zto # z the #zdetriment #zof #zthe #zsystem's #zoperation. #zImplementation, #zoperation,
#zand #zmaintenance # z plans #zmust #z(at #zleast) #zinclude #zcareful #zdefinition #zand #zdescription #zof
#zthe #zactivities #zrequired #zto #zimplement #zthe #zdatabase #zdesign:
• loading #zand #zconversion
• definition #zof #zdatabase #zstandards
• system #zand #zprocedures #zdocumentation: #zsecurity, #zbackup, #zand #zrecovery
• operational #zprocedures #zto #zbe #zfollowed #zby #zusers
• a #zdetailed #ztraining #zplan
• identification #zof #zresponsibilities #zfor #zoperation #zand #zmaintenance.
3. What # z major # z factors # z should # z be # z addressed # z when # z database # z system # z performance
# z is # z evaluated? #zDiscuss #zeach #zfactor #zbriefly.
Database #zsystems #zperformance #zrefers #zto #zthe #zsystem's #zability #zto #zretrieve #zinformation #zwithin #za
#zreasonable #zamount #zof #ztime #zand #zat #za #zreasonable #zcost. #zKeeping #zin #zmind #zthat #z"reasonable"
#zmeans #zdifferent #zthings #zto #zdifferent #zpeople, #zwe #zmust #zaddress #zat #zleast #zthese #zimportant
#zperformance #zfactors:
• Concurrent #zusers
For # z any # z given # z system, # z the # z more # z users # z connected # z to # z the # z system, # z the
# z longer # z the # z data #zretrieval #ztime.
• Resource #zlimits
The #zfewer #zresources #zthat #zare #zavailable #zto #zthe #zuser, #zthe #zlonger #zthe #zaccess #zqueues #zwill #zbe.
• Communication #zspeeds
Lower #zcommunication #zspeeds #zmean #zlonger #zresponse #ztimes.
• Query #zresponse #ztime
Queries #zmust #zbe #ztuned #zto #zprovide #zoptimum #zquery #zresponse #ztime. #z(See #zAppendix #zC,
#z“Database #zPerformance #zTuning.”) #zLack #zof #zquery #zresponse #ztuning #zmeans #zslow
#zresponse # z times. #zDepending #zon #zhow #zgood #zthe #zdesign #zand #zthe #zprogram #zcode #zare,
#zthe #zquery #zresponse #ztime #zcan #zvary #zfrom #zminutes #zto #zhours #zfor #zthe #zsame #zquery.
4
