在定义一个关系结构时,应该说明 ( )

A、字段、数据项及数据项的值
B、属性名、属性数据类型及位数
C、关系名、关系类型及作用
D、记录名、记录类型及内容
查看答案
正确答案:

B

答案解析:

暂无解析

上一题
你可能感兴趣的试题

Ifyoudonotfindtherequiredinformationusingthetipsfromtheprevioussection,thenyouneedtoconsultanonlineservicetofindthepieceofinformationyouwerelookingfor.Threedifferenttypesofserviceshavebeenestablishedovertheyears:crawlers,directoriesandmetasearchengines.Thefirstcrawlerwascreatedbackin1993.ItwascalledtheWorldWideWorm.Itcrawledfromonesitetothenextandindexedallpagesbysavingthecontentofthewebpagesintoahugedatabase.Crawlersorspidersvisitawebpage,readit,andthenfollowlinkstootherpageswithinthesiteandevenfollowlinkstoothersites.Webcrawlersreturntoeachsiteonaregularbasis,suchaseverymonthortwo,tolookforchanges.Everythingacrawlerfindsgoesintoadatabase,whichpeopleareabletoquery.TheadvantageofthewebcrawlersisthattheyhaveanextensivedatabasewithalmostthecompleteInternetindexedinit.Thedisadvantageisthatyougetthousandsofwebpagesasaresponseforalmostanyrequest.Webdirectoriesworkalittledifferently.Firstofalltheycontainastructuredtreeofinformation.Allinformationenteredintothistreeiseitherenteredbythewebmasterwhowantstoannouncehisnewwebpageorbythedirectorymaintainerwholooksatthewebpagessubmitted.ThedirectorieswherewebmasterscansubmitboththeURL(UniformResourceLocator)andthedescriptionnormallycontainmoremisleadinginformation.Gettingintomostwebdirectoriesisacombinationofluckandquality.Althoughanyoneisabletosubmitawebpage,thereisnoguaranteethatacertainpagewillbeincluded.Somedirectorieschargeforsubmission,whichisbasicallyarip-off.Somecrawlersmaintainanassociateddirectory.Ifyoursiteisinthedirectory,therankingofyourwebsitenormallywillbehigher,asitisalreadypre-classified.Manydirectoriesworkwithcrawlerstogether,inordertodeliverresults,whennothingcanbefoundinthedirectory.MetasearchenginesdonothaveadatabasewithURLsanddescriptions.Insteadtheyhaveadatabaseofsearchengines.Ifyouenteryourkeywordsintoametasearchengineitwillsendoutrequeststoallthedirectoriesandcrawlersithasstoredinitsdatabase.ThemetasearchengineswithamoresophisticatedapplicationinthebackgroundareabletodetectdoubleURLswhichcomebackfromthevarioussearchenginesandpresentonlyasingleURLtothecustomer.

34.Crawlerisakindof__________.

A.wormB.searchengineC.serviceD.directory

35.ThedisadvantageofCrawleristhatit__________.

A.providesacompletedatabase

B.takestoomuchtimetofindtheneededinformation

C.providestoomuchuselessinformation

D.givesresponsetoeveryquest

36.Whocaninputinformationtothewebdirectories?

A.Onlywebmasters.

B.Bothdirectorymaintainersandwebmasters.

C.Anyonewhowantstoannounceawebpage.

D.Anyonewhohasfoundanewwebpage.

翻译:invain

视力;洞察力n.v_______________

多层库房的层高是指()

A、下层楼地面至上层楼地面的高度
B、下层楼地面至上层楼板地面的高度
C、下层楼地面至梁底面的高度
D、库房的净高

完型填空(本大题共10小题,每小题1分,共10分)从选项中选择一个最适合短文的选项,错选、多选或未选均无分。

Joggingisbecomingoneofthe___21___growingactivitiesinthenation.Morepeoplearestartingjogeachyear.This,however,isarecentoccurrence.Itwasnotlongago__22____joggerswereraresight.Somepeoplethoughtthattheylookedquitestrange.As__23____peoplebeganjoggingthesightofthembecamemorecommon.Therearemanyreasons___24___apersontotakeupjogging.First,itisagoodformofexercise.Thisis__25____itinvolvestheuseofmanypartsofthebody.Theexercisingoftheheartisofgreatbenefit.Thisisoneofthemostimportantpartsofthehumanbody.Iftheheartdoesnotgettheneededexercise,seriousproblemscanoccur.___26___reasonforjoggingisforenjoyment.___27___beinggoodforpeople,itcanalsobeverymuchfun.Partofthefunofjoggingcomesfromtheopportunityitprovidesformeetingotherpeoplewhoenjoyit.One___28___thatshouldbeconsidered___29___apersontakesupjoggingasaformofexerciseofenjoymentisthatitisnotforeveryone.Peopleshouldfirstcheck30theirdoctorsandbepreparedtofindanotherformofexerciseifjoggingisnotrecommended.

21.A.fastestB.quickestC.mostD.best

22.A.whenB.whileC.thatD.as

23.A.manyB.thoseC.moreD.the

24.A.ofB.withC.forD.in

25.A.thatB.whyC.reasonableD.because

26.A.AB.OtherC.TheotherD.Another

27.A.ExceptB.ExceptforC.BesidesD.Regardlessof

28.A.matterB.eventC.thingD.occurrences

29.A.ofB.thatC.whatD.when

30.A.outB.overC.onD.with

热门试题 更多>
相关题库更多>
网络技术
数据库
信息安全技术
软件测试技术
试卷库
试题库