Buffer Management in Multimedia Database Systems

Abstract

The delivery of continuous and synchronous multimedia data from a database server to multiple destinations over a network presents new challenges in the area of buffer management. Many factors that were not considered in conventional buffer management must be examined. In this paper, we investigate the principles of buffer management for multimedia data presentations in object-oriented database environments. The primary goal is to minimize the response time of multimedia presentations while ensuring that all continuity and synchronization requirements are satisfied. Minimum buffering requirements to guarantee the continuity and synchrony of the presentation of multimedia data are first proposed. A prefetching technique which satisfies these requirements is then developed. These principles and technique provide users with the full range of information required to develop a database environment for multimedia presentations. 1 Introduction Advances in multimedia computing techn...

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SreenivasGollapudi andAidongZhang
DepartmentofComputerScience
StateUniversityofNewYorkatBu?alo
Bu?alo?NY?????
fgolla?s?azhangg?cs?bu?alo?edu
Abstract
Thedeliveryofcontinuousandsynchronousmultimediadatafromadatabaseserverto
multipledestinationsovera networkpresen tsnewchallengesinthe areaofbu?ermanagement?
Manyfactorsthatwerenot consideredinconventionalbu?er managementmustbeexamined?In
thispaper?weinvestigatetheprinciplesofbu?ermanagementformultimediadatapresen tations
inobject?orienteddatabaseenvironments?Theprimary goalistominimizetheresponsetimeof
multimediapresentationswhileensuringthat all contin uityandsynchronizationrequirements
aresatis?ed? Minimumbu?ering requirements to guarantee the con tinuity andsynchronyof
thepresen tationofmultimediadataare?rstproposed?Aprefetchingtechniquewhic hsatis?es
theserequirementsisthen developed?These principlesandtec hniqueprovideuserswiththefull
range ofinformationrequiredto developadatabaseenvironmen tformultimediapresentations?
?Intro duction
Advances inmultimediacomputing technologies have o?ered newopportunitiesto store?manage?
and presentmultimediadata indatabasesystems?Ithasalreadybecomeevidentthat object?
orien teddatarepresentation andmanagement providesapromisingapproach to themanipulation
ofmultimediadata?Tosupp ortits ?exibleretrieval?con tinuousmediadatam ust?rstbe parsedin to
represen tablesegmen ts? whichwe term media objects?In order tore?presen ttheoriginaldatastream
tousers?synchronizationconstraintsamongmedia objectsmustbe speci?edandmaintained?Such
synchronization isusuallytermedintra?stre amsynchr onization? Anadditional complication arises
withthetiming relationshipsthatmayexist amongthe di?eren ttypesofmediadatastreams?For
example?manymultimediaapplications?such asrecordingand playback ofmotionvideo and audio?
slidepresentations?andvideo conferencing?require the synchronizeddisplay ofmultiple media data
streams?However? suchmediadatastreams maynotbe mergedpriortostorage inadatabase?
and suchamergerwillv astlycompoundthedi?culties ofretrieving componentmedia? Thus?the
synchronization ofmultiplemediadatastreams?termedinter?stre amsynchronization?becomes an
essentialprerequisitetoanysuccessfulmultimediadatabaseapplication?LG??b?LG??a??
Bu?ermanagementwithinthemultimediadatabase system is essentialtoensurethemainte?
nanceoftheintra?and inter?streamsynchronizationrequirements ofmultimediadatapresentations?
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spacem ustbesu?cienttosimultaneouslyholdallthesestreams?Furthermore?anappropriate
allocation and replacement strategymustbepro videdto anticipatethedemandsofdelays anduser
interactions? Suchastrategymust minimizetheresp onsetimeofmultimediapresentationswhile
guaranteeingthatallcontinuityandsynchronizationrequiremen tsaresatis?ed? Th us?thecentral
issuesinthis contextinvolvetheprovisionof e?cientpreloadingand replacement mechanismsfor
cachingmedia ob jects?These mechanismsare in tendedto ensurethatthe de?nedcon tinuityand
sync hrony ofmediastreamswillbepreservedtothegreatestextentpossible?ev enif there areuser
interactionsandloadingdelays?
Research involving bu?ermanagement inmultimediadatabase systemsisstill initsinfancy
?TK???? Moser etal?MKK???haveproposedabu?erstrategy termed ?least?mostrelev ant for
presentation??Thisbu?er strategy investigates thee?ects ofsuchuser interactionsas ?rewind?
and?fastforward? onbu?er design?A mec hanismisproposedwhichreducestheensuingdelay
afteruserinteractions?Chaudh urietal ?CGS???haveinvestigatedtheproblem ofcontinuously
displa yingcompositeobjectsthat aredynamically speci?ed atthe serv erlevel?T echniques based
onsimple slidingand bu?eredsliding are proposedwhic hsupportcon tinuousdisplaybypartial
prefetc hing ofoverlappingmediaobjects? Such anapproach ispreferable to the naivestrategy
ofprefetching the en tirety ofoverlapp ed media ob jects? NgandY ang ?NY??? have attemptedto
maximize bu?eranddiskutilization within theconstraintsofa?xedamountofbu?erspaceand
diskbandwidth?b othofwhich arepre?determined in thedesignphase?Prefetchingstrategiesthat
areapplicabletodatabase systemsareproposed whichmaximize the throughputofthe system?
In thispaper?wesystematically studytheprinciples underlyingbu?er managementform ulti?
mediadatapresentation in object?oriented database environments? Mediastreamsarestored as
sets of mediaobjectscoupled withspeci?edsynchronization requirements? Complementarytothe
workproposedbyChaudhuri etal?CGS????we investigate theminimumbu?ering requirements
that are necessary toguaran teethe contin uity andsync hrony of the presentation ofmultimedia
data? This isaccomplishedby ?rstdetermining theminim umconsuming times ofmedia objects
following their loadingtimes? while guaran teeingthehiccup?freepresen tation of the mediastreams?
The presentationofb othasinglemedia streamandmultiple streams with or withoutthee?ectof
delaysareconsidered?Wethenstudytheprinciplesofmedia ob jectsconsumption?Least upp er
boundsonbu?er sharing amongmediaob jectsare de?ned? Theseminimum bu?ering requiremen ts
establisha framework forbu?er managementinthemultimediadatabasesystem?Aprefetc hing
tec hniquewhichsatis?estheminimumbu?eringrequirementswillbedev eloped? Theseprinciples
?

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modelstobeused inthispaper?InSection??wepresenttheprinciplesof bu?er managementfor
individualmediastreams?bothwithorwithoutdelays?InSections??wediscussbu?erconsumption
formultiplestreams?Section?presen tsabu?erallocation andreplacementstrategy? Concluding
remarksanddirections forfutureresearch are o?eredinSection ??
?The SystemandData Models
Inthissection?weshallintroduce thesystem anddatamodelsthatwillbeusedintherestofthe
paper?
Thesystem architectureunderconsideration is illustratedinFigure ??This architectureincludes
a centralizedmultimediadatabasemanagementsystem ?databaseserv er??amultimediadatabase?
andasetofclientswhichaccesstheserver? Withinthemultimediadatabasemanagementsystem?
amultimedia pla ybackmanagement functionisin tegrated intoanobject?orien teddatabasesystem
?OODBS??Thissystemis curren tlybeingdesignedandimplemen tedontop of O??aw ell?known
OODBS?How ever?the design strategiescanbe appliedto anyOODBSenvironmentthatsupp ort
aC??interface?The system isdesigned tohandleimage? audio?andvideo media objects?
Multimedia database
Database Server
Network
Client 1Client 2Client 3
Client n
Figure ??Systemarc hitecture
?

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videostreamcanbesegmented in toasetof atomic ob jects?each ofwhich containsa setof video
frameswith speci?cseman ticmeaning? Similarly?acontin uous audiostreamcanbesegmented
in toaset ofatomic objects?each ofwhich con tainsa setof audiosampleswith sp eci?c semantic
meaning?
Theatomic ob jects withina media stream arelinkedtogether through synchronizationtime
constraints?Theseconstrain ts may specifydiscrete? con tinuous?ov erlapping?orstep?wiseconstan t
time ?owrelationshipsamongthe atomicobjects?F orexample?somemultimediastreams? such as
audioand video?arecontin uousinnature?inthat they?owacross time?otherdatastreams? such
as slidepresentationsandanimation?havediscrete?overlapping? orstep?wisetime constraints? It
may? for example?benecessary todisplaytwodistinctslide objectsjointlywithinasingle slide
presentation stream?Ingeneral? thetemporalrelationshipb etw eentwoatomicob jectsina single
stream may conform toany of thethirteen temp oralrelationshipsdescribed in ?All???? In our
representation?eachatomic object isassociatedwitharelativestarttime anda time interv al which
speci?es theduration ofitsretriev al?with theinitialatomicobjectsinthe mediastreamassumed
to startattimezero?Theactualstart timeofamedia object isusuallydynamically determined?
Onceamedia streamis inv oked? it isasso ciatedwith an actualstarttime?eachmedia object within
thatstream willsimilarlybe asso ciated withan actualstarttime?Weuseho? t??titodenotethat
objectois tobe deliveredat timetandwilllasttimeperiod?t?
Mediaobjects fromdi?erent datastreamsma yneed tobe linkedthrough timeconstrain tsto
specify their synchronization?F orexample? inslidepresen tationapplications? anaudio objectm ust
beplayedalongwitha slideobject? The temporalrelationshipb etw eentwoatomicobjectsfrom
di?erentmediastreams mayalso conformtoany ofthe thirteentemp oral relationshipsdescribed
in?All????Synchronizationrequirements maybe speci?edas meta?data or speci?ed intransaction
programs? In somecases? the relativetimeand timein terval associated withan atomicobjectmay
needtobeadjustedtoconformwiththesesynchronizationrequirements?
?Bu?erModel
Inthis section?we willdev elopaframew orkwhichgeneratesthe requiredstart timesfor media
objects? This framework guaran tees thecontin uity of mediastreampresen tationwhileminimizing
bu?erutilization?We assumethat eachmediastream issegmented in toa set ofmedia objectsin
them ultimediadatabase? Thus?theprop osedprinciples aredev eloped at theob ject level rather
?

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