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··~·ALI UNAL. M. Sc.•
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Submitted to ~he School o~ G~aduate Studies 1n
~ ?a~tial FU1~i~~ent o~ the Requi~cments
-!'o: the Degree
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CENTRALISED TIME'SERIES MANAGEMENT FOR CONTINUOUS HYDROLOGY
ON PERSONAL-~ICROCOMPUTER NETWORKS
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-DOCTOR OF PHILOSOPHY (1985)(Civil Engineering)
McMASTER.UNIVERSI~Y
Hamilton. Ontario
,;
•TITLE:
AUTHOR:•
Centralised time series management for continuous hydrology onpersonal microcomputer netvorks.
Ali Unal.
B. Eng:. COrta Dogu Teknik Universitesi. Turkey)
, "" M. Sc. (University of
,111ln01s at Urb~~a-Champaign. USA)
.",,,
< '-SUPERVISOR: Dr, .... JaJ:les
,-
.-.-NUMBER ,OF PAGES: XIV. 170
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_ ~ABSTRACT •"
:....-
Continuous~ hydrology packages such as. Hyd~olog1c Simulation, /
Prog~,am--Fortran. EHSPF) and Version 3 of f:he'StoJ;.m Water "Management Model
(SWMM3) require extensive comPuting t~m~ even for certain" cases of event~
•modelling. 'In their original sequential. time-sharing. computing schemes.
CO~~i~~~US modelling applications required a prohibitively expensive;~"'.,
overatl turn-around ti~e a~d an overvhelming amount of manual
Input/Output (I/O) time series (TS) data management effort. By
decentralizing the processing. avo1din~ a time-sharing computing
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environment. a~d finding vays to keep track of I/O TS data as part of the
processing. these problem~ can be overcome.
Computational. Hydraulics G~up Time Series'M~~ager ,(CHGTSM). a
~
Database Managemen~ Syst~m (DBMS), vas developed by the present author to
proviqe easy ~~cess to TS data. independent of details of~storage. CHGTSM~ ~
, A'
is based on ~~ unconventional" data access technique. also developed by
the author, that h~~dles variable resolution continuous TS records. The
CHG ,Time Series ·Store (CHGTSS) is prepared by · ..·the CHGTSM. CHGTSM is
applied succesfully, In a case study, CHGTSM saved 88~ in hard disk
storage compared \ 'to the ra.... database. ""'C~GTSM serves event as ....ell as
continuous mode~"l1ng applicatio~·. A' rnan~al for CHGTSM is "also ....ritten by
the presen~~author.. 1':
CHGTSM can be. used. to .-d·istribu"te th~· database to the .riodes"~ of a
".'" .ll'nked c~nfi&ura~1-on .t)f ·microcornput.e.r~. D1stributed process1.ng.· (DIS?) of
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'cent,alized data is made possible by CHG Distributed Data Processing
Soft~are (CHGDPS). CHGDPS. developed by the present author. is a shell
around CHGTSM which includes,security,,-
provisions ~d nOd~ synchronization."assistance. The simulation of a DISP application for continuous
hydrologic modelling in a 'L'ocal ,Area Net~ork (LAN) improved the' computing
efficiency by 54~ compared, to sequenti~l'processi~g. :CHGDPS vil~ allov
true concurrency only through a batch application.
CHGD?S sync~rorrization assi~~ance relies on i~ming relations of
the com.Eutational modules . that are ~ accessing _.the system. A program
measurement (PM) t.echnique \las a~apted. enhanced and applied by the
present au~hor.to otrt~in the ~iming.~elations. Suph DI~P control helps
the user to optimize over~l~~sys~em processing. Fo~ example. ~HGDPS may- . ..~,
decide (or' help dec.ide~ a shift from one computational approach to·
~~other for consideratio~s of time. spa~e. numerical stability. and
, ,accuracy.
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~.'
.·The DISP scheme i-s flexib!e\~~d can~- ... .,........ .;.-
.: . .~... '
computers e.g.... -LAN' s.~ :.'~ ~-,':
be implemented on ~~y linked
distributed data gathering and
, '.'Computational Hseto}cigy Work Group System (CHWGS) is assessed as an-real> time control (RTC} devices. ~~e vhole system. called the
t,
-.:,- . -,
enviro~m~nt ~or coritinuous (or event) hydrologic modelling.
data gath''':;:ing- and distributed RTC.
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-ACKNOIILEDGMENTS
I vould like _to thank ~y supervisor Dr. Wm. James fo~ his
continuing ~ssistance and,
encouragement throughout the York.• I would
also like. to thank my supervisory caromi ttee members. Dr. P. H,amb11n. Dr.
S. Poehlman and Dr'. B. Szabados for their. valuable advice. 'I,
Thanks are due to Dr. R. Johanson and U.S Army Corps. of Engineers
Hydrologic Engineering Center for their generousity in supplying the
documentation that I have requested. "
Several members of CRG contributed to CHCTSS by collecting and
rs~oring ~he da~a. Special ~hanks ~o Ms. Chris Dziura and Mr. P.
Ni~~richter for bUilding Hamilton ~~d Toronto· ~atabases. Thanks are
extended to Metro Toronto Department of Publi~ works for supplying the
~~o da~~.
Th~~ks are also extended to Mr. M. Robi~son and Mr. M. Stirrup
for t;t:lJCir... suggestions.
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TABLE OF CONTENTS·
t
"ABSTRACT
ACKNOWLEDCEMENTS.
LIST OF TABLES
LIST OF FICURES
PREFACE
1.-INTRODUCTION
"
\.'~'.
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".. ' Pa&e
?"
(iii)
,(v)
(x)
(xi)., I:
(XiV)
... 1 . 1 P~oblern description
1.2 Identificati~n Of. solutions
1 ,:3" S~UdY procedure'.
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5
6
",
1.4 SCO~~~ and·~he limitations of the study" •
•
7
2. BACKCROUND,< .. .,.-
2. 1 Evolving cia t'B.·· environment .fot' cont.UJ.uous hydrologjt?., '
2.1.1 Continuous modelling an~'~vent modelling
-:.' '.2.1.2 Continuous models"•
2_1.3 Va.ria.ble~t~mp6tal and spatial r;solut;on ..
-,
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2.1.4
. ,
HSPF da~a managemen~ approach for. ' . cont~nuo~~" mo~ll in~.:-. . ' ~ .. ....
2.1.5 Real-time contral i,o ·urban ....ater sj"stems'
"
Data ~ollection. tra~smission .and storage..... ... ".
2.2 Data gathering
2.2.1
...,;:.. :."
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23
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• .For a ;.description 'of acronyms used ..~ :' ,
(vi)
see List of Abbrevi~tions.~ ..
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2.4 :Computer networks ~~~ distributed processing
: '2.6.3 An approach to re-evaluate solutions
24
25
26
27
29/
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31
31
33
36
36
39
39
40
41
43
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45
46
46
50
58
63
70
71
72
I
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CHGTSM da;a comp"essio~" '
Structure of', CHGTSS, '
Dynamic flow routing ~"
'irIME SERIES ,MkNAGEMEN.T',_
3.2,6" DBASE III and, CHGTSM
3.2.3 CHGTSM programs
2.6.1) Determining equations
'3 ~ 2,2 LeveJ.'s of s·torage,
"
2.5.1 Baslc con~e~ts~
'.2.~.2 Centralized ~etwork control
,2.4.1 ~as1c principles of computer networks
2.3.1 Basic concepts
·3,2 ..4
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"3.2,8 I/O handlers~ ,_
·Z.6.~ Solu~ion of the St. Venant equations
'1:'2."' ~Introduction
.,3,2.5 Query attributes of' CHGTSM
\,. ',,
2,2.4 CHG data collection
2,-3:3 E"isting DBMS's,
3.1 Design requirements for ~SM •
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3,2 .cHGTSM
2.3 Data~ase management systems
~ 2.'.2 Database structures
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2.5 ?'rogram measuz:ement
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4.2 PM results
4, PRQGRAM MEASUREMENT
4, (2 The PM techniqU:,,'<."
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,Case tor P~.,
{Introduction, .,4, 1 ,1
4.1.} The ap~lfcation me~hod
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4.2.1, General ;~~ults
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4.2.} PMRUNOFF, .... ~4.2.4 PMRAINPAK
4.2.5 PCrFMl timing. ,
.,
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-,4~~'6 P~on numerical ~pproaches to dynamic routing'
5. DISTRIBUTED PROCESSING OF CENTRALIZED DATA
5.1 .~Case for a special ~ont;ol'systeQ "..
,5.2 ChwGS
,-
5.2.1 }ntroduction"
,
5.2.2 CHWGS hardyare
5.2.3 CHGLAN,,'
5,3 CHCDPS
5.}~1 Introduction
5:3.2 Operations of CHCDPS
5.3.3 Securi~y provisions in CHeDPS'. '
5.3.4 PM provisions in CHCDPS
5.3.5 Overall operation of CHGDPS
5.3.6 ChVCS va Qequential computing
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(viii)
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.,6.2.1 Que~y operations
/,6. j1-PPLICATIONS TO cOttPUTATIO~L HYDRAULICS '.I CHWCS enviro,nment f ' ,.
;76.2 Query' and~compU.tationa:l-operatio;;',; of .CHGTSM-
"
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6.; CHC.TSS"
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. ~:,3.2 Toronto"
6.;.; 'comyres~ion
" 6.4 . .cficTSM 1/,0 Handlers
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6.4.1 .Input ha:;dl.ers
6.4':2 Output.··handlers. ,
6.5' C~se studies u;in~ CHCT~M~ . .
6..5:1 '. Chedoke C'<eek. Study .•..
6.5.2 To~onto Study .•
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7. CONCLUSIONS' '.
7.1 Evolving compu"Ci!1S envirc;mrnen,t for .ChW'G$ 's'
7.2 C!iWCS
7.3 An evaluation of the study
REFERENCES • J,.../
161
. LIST OF ABBREVIATIONS 167
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. I(ix)
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• LIST OF TABLE~· . P,,&es
...... , 4.1
Disk space allocations for CHGTSM.
Using LINPACK in half precision.
72
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5.1 Net~ork characteristics of Net~are.
5.3a Computation times for sequential processing.
5.3b Computation times for 'distributed processing.
5.3c Simulation of the DIS? problem.
6.1 Toronto rainfall data.
"
*.For·a description of acronyrn~ used. see List'of Abbreviations.- ~. ' :.
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'09
129
129·
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Pac;e·
..4
11
1 1
14
1:f
19
22;...• .".- .22 -28
.,.
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30 ".... 30
33 "
33
"..,.....;. 35",
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.session.
Options for tapping a rnai~frame database.
The three best kno....n database approaches")
',.Three levels of database architec\u~e.
Typical control loop in a combined se\.1er__:sys"tem.
ANNIE - Sample
......
Centrali~ed vs distributed RJC system.
Activities involved in a HSPF operation.
Comparison of observed and computed peak flo~~.
Overview of PCSWMM3.
LIST OF FIGURES·
Centralized database fo~ a net~ork of microcomputers.
3.2 Levels of sto~age in CHGTSS.
2.13
2.10
3.'· A relational database file.•
2.12b Possible topologies for communication subnetsusing broadcasting.
2.12a Possible topologies for a point to point subnet:
2.9 DBMS stored-record interface.
2.'1 Architecture of a typical mainframe DBMS.
2.8
2.7
2.4
2.5
2.6
2.3
2.2 Overview of HS?F.
)-'2.1
•
3.3a Logical viev of type di~ecto~y....' 49
3.30 Logical vi~~ of uppe~ pa~t of TSSDIR. 49, "
.'. ,...,..-.
• Fo~ a desc~iption of ac~ony~s used. see List of Abb~eviations.
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;.4 Relations which qualify a sp~~ of TS data. 51
Logical viev of a tuple for permanent data.
Logical vie'w" of"a tuple for temporary data.'.r 0.:-
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60
52
52
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.,CHdT~ information flo~.....
Structure of a secondary label.
·;.7a
...... -.5.7b; ....'
3.7~ 'Control variables ~n a TS record. 60
3.8. :..-.Portion of QRETRIV output f~le.....~ 69
85
79
78
91
.'- "
..FOR'J;.~~ code fo;' .'<!Ibroutin·e DEPTH in EXTRAN.
~..
4.;
4.1 a-; ."~'.'-, P,' ......._ .... ,H
.}4. 1b J PM--: p~ocedure fo-r D"SPTH ..~- ,,..;..... :;... ._" .'-
4. i'~' Master Oavchart" 'fo;- EXTRAN..~... ".;;;;...; ..
Var iat lOrj 0:::' ...;.:t( EXTR.AN) .~~ ~ .. ,
. --V7'
.,.~,'-.:~.-.".. .,.",
.... :.:""-"
; 4.4 PME~TRAN for C~~E~~1~2 and CORONA PC. 92
The secur;ty p~ovisio~s in CHGD?S.
Retrieval of a TS'file in DIS? mode.
Directo~y recor~ for processed TS data during DIS?
128
98
125
'17
122
120
120
113
112
10;
10;
\
_.
eHG Ha~il~n dat~ acqui~i~ion·system.-
?repan:C~io:'l of a TS fi:ie ... in·DIS? ....-:tode.,
Directory record ~or ~~ticipated TS data d~ring DIS?~
PM for expl~ci~.EXTRAN.
Flowchart of CHCD?S.
/ ..~'Conceptual represen~ation of EXTRAN ~odel.
!-M ~or implicit EXTRAN .".
Architecture of CHG~?S.
4.5
4.6a
4.6b
5.1
5.2-."5.;
5.4a
5.4b
5.5
5.6
5.7
/-".6 .J.;.'
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Storms ~s identified by CHCTSM.
Sample CHCTSM/userinteraction.
.'Toronto storms ranked by volume.
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~ .1 41
143
146
147
,.. 149
149
150
:
; { /, .modea11ng ~ith S~~3.
"
iStacks for s6r~~ng by maximum intensity~
Output operations by cHCTSM. "..
TS for isolated storms (events.)':
CHCTSM output for continuo~
,.,
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"~.." "':.:.~.,
:PREFACE
.' "
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Database Syste~s". tpe.ijYdrologic Sirnul~tion Pr95rarn-Fo~ran (HSPF) o~ US
term1~ology varies among the user community.
•...
..., ,
to
Most 'terms
Introduction"An
.'
are ad,aptec"-f:-om Date:
. '".f'
,~ ~'Patabase
:!'>
and~efinitions:7sed
"
Environtlental Protection Agency (EPA) a.'1d the data managemen't routines- of~ ~',
Hydrologic Engineering Center (HEC} of the US Army Corps of Engineers.,"
f, Quotations that have been abstracted and/Or adapted frorn'10 of the.'
.'.,
~riter's papers are credited in the te~t and in the list of references .
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, INTROOUCTHj/>
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(James ":a."d ..Unal-;... "' 984a"..b),,: ... '." ;:: " ," oJ
,. '
..:.; The general pr'9c.ed~e us:ed in.'·~his study-".
..r : .',". ~ ..~:
evalved f::;om::·the •.~.r ~ ~,~r •s.',
." - 0' 1 .,
beloY is '~bstrac~ed with'ml~~r chang~s.frorn these.pip~rs.. ,"... '.. '.. -' ", ...... .''-'
••.. Sect.ion ," , _,
... .'. '.
.."
ins'trUmentation;' f1 eid
~'c-' ,...• r-o.,.".'.' '. . '... . ".I . •_........ :l:i:":§loee",ln-g: .. ."..' .-.
.. .mic~oprocesso~-based
'of . :fUndamental.
hydraul ics .and hy·c.r0 fo,gy, ·.i~cl U:de.~ . - r"
.'"
Sl'tuatlons. a~d modelling:
"
3.cccssion; aDp~ t·catio:-:. progra..":l SY5tCrolS..' ...., .'
documentation and reporte----.
..o.c..",er a~ ion:,
text' processing;. ~ - ..-,
and,-
~eal-time control~f ~ater systems.
t\pplication programs c~r~ently 'vid~ly useq in Civil ...¥. ..:.nglneerlng~
computational hyd::-aulics include processes usually subs~~ed under
~... dlsci~lin~s of ~eteQrology., .. , ,., ..exa.":lpLe • -""a~e.r.5 dl"~tr i cut 10n-,
,-
q~~lity cO:1~l"'ol,
.-coasta'i ~.nd tldal .c;:.g.lneerlng.
, . '" ' . ,.... ...draindge net""ofks.'""atet and.~aste""ater treatment pldnts,
.. " J .. • •
urbanstations,
·•..ate:"'.,.
-. "
ove;al'.1".....eViden.-=.
~
.~ '-I i·ttle or :10-
sys-:,.cms,
acquisi tio"n' "anc."1 management.) ~ is" ..-' .. .. .
and s·oi't...·ar ~ s;y·st..e~s are.· ondef'gqiJ'1g r ,;P i d d-e.,;.e"l,opment.~:1, ... ~-.......
bUild:ng (;ncludi~g data
'.1 •
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-,
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, '... .;". ....
"Certainly no perrormance evaluation ot such general sys~ems 1u~' being
"attempted,,.
~,
continuous modelling as, .." W'ell.:as event c'odelling: Even~'- Q9del11tl.g is'.. ~.. . .
assoc~~ted: with ~th~~tr~~it~onal desi£n stor~' p~losdphY ",~er; ,startup. ," .. • .,' 1'., ~ .. • .' '.';'
,:va14es must, be" ~s~1mat7ed..· C~ntinuo;s' "modei ling r~'quire~; use .... of'_'available
'.
of
Hube;-
"
see"
used.,',
ac~.:myms:
"
of
. .:. ,"
'.. ~
.~ J' •
S1oIMM~' (Johansol1 et: ,!-l," 1981;. .' .,"
"'. . ~ ~progr",,;:' '..pack~es j fn ,';- the
.~.. .-r~~ent,XY d~veloped in a·: reC16~e batchwer e
description.
e,g, HSPF. and
" ,
operat1o~al or appli6ation pr~grarn systems
a
area
Fo%'"."
, ..
large'
mainframe env1roncent.
hydrau~i~s/hydrology
'Abbreviations. - These
"
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1982), ~he current
:., .,,:
attractive (~~~es:
.:, ......records
..p;o:cessing f.a ,.m.Uch;.mor·e
'" .
-,tRobinac;n and JomiS', 1981 r,
•
tn the pas:', ·hYdrOlogiCail.m~de~ling h~:> been mostly r'e<;tricted to'
. . ~ ..,." .'. '. . '.. . .di,screte events. HO'Jev,e:r. \lith the~ il:lpr~ved .affor_daQ.~lity"of cooputi'ng.... ," ... . . (
continuo~us
"
".,"
"
,-,
.... 1l-as pro.....~n!~uch more' problematical t.ll'~ th~ ~r·elatrvel'y._6imple engi.neering.., ,. ,.:-'"and sdenUftc, algoritltms and r.outin.es tn>ically include-d 1,n ,tQe large
;.
A very-large p'ortion of this data is"
of
",time series (TS) in natUfe artd reqUires.
transition to contlnuo~! model;tng nov fores~ad~~~ dif~icult ~:oblema... p ,,'"
,';~pu't/OJi'tPut~~I/P) data '1:l"';'ageine';~_. '., ~'. .":'0' ......
",
:;
"
"
system packages. ,-The app;1cations of the principles of the DBMS"s' and various
.,linked configurations of PC's (i.e. LAN's) appear to offer a reasonable
.' ,
. J' al t-ernative. In cost cases. the cost performance of poverful PC '.s. w.i:th a....'" .:/".
ce~tral hard disk system. and using the nev generation of integrated. .
'/"1 ,a,..,-..' ..
",".."". "
'.,
.:..
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. '
.." .... .,;.
'.:~ 80r~are, is eV1de~~i.s>-better 'than- tha~' of mainfr~ea_ '. '''l,
'"
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,;.1.
.-" ,,
,:..."
." .-"
..~..-"
~he ' aya'tem a'tudied b.ere ~a a -.>e'tw~rk of'microc;;""u'tera connec'ted: ;. .... ''''~' ." .' .. ~: ....:' -
a cen'tral 4iak~opera'ting aya'tem func~ioning on ~:.erver (aee :-tfgm:e
logicalofco~pu'ters executes-a separable block.... '. . . . .nodal, ,
eaeh
, ,:',.1). T~e aya~em primarlly:'''';;liea on a D!lf'lS,;.moa't'of wJ:;fch ia devo'ted"'to
. ,,'. ..' . . .... '.' .~. , .TS da'ta: mana&emen't. : l/hUe'the aerver' holda ,tne "eWork opera'tiiig ays'tem.,
. '':'.,' . :. ..... . .."
tt\e
-,..-..
:
-,
Th~ routines may involve data
.' .," .... ,.acquisi tion'.
. ... :"
which it is dedicated...,runoff . '''.,modelling. transport or
ar'ainage. . syS"'tccs net~6rks':," ) ."
water quality modeJ'li ng. cos't-benefi t
;, ,!' analyiis / or s't';'Ustical p.os't-processing." . "
enY'ironment.... vith.'
mul'ti-processing
'the .. 'traditional
.'i'tS mul 'ti-uaer." and
DIS?," has evolved frombllJ3ed,-Microcomputer-.
-~
~maint'rame:
". capabir1Uea (i.e. mUl1;i-tasking). The mainframe database used,'by a group
. .. ~,
of eng~eers.or sc1ent1s~B 1s also ma1nt~1ned'on apentral disk system,with magne:ic 'tape backup capabilities. Such a 'da'tabase could be made
"
coherent and available to every member of the resear~ and developmen't"
,
",- group with appropriate security safeguards,
For ex~ple. for a concurrent ~rocess1ng application, software can
, , .pe writ'ten to ensure that 'the ~elevan't P?rtion of 'the TS oU'tput from~the
,'lqg,ically preceeding block of prQgrams (for example. 'the precipi'ta'tion
c""
analysis)., ia properly" completed befo"e 'the logically SUbsequent
computational procedures are allowed access to that TS (for example. the. "
, 'rainfall/runoff moQelling). Thus a series of computational modules could
access to a cen'tral TS database in which the first input TS segment is
~~alysed for precipitation by a module. ~~d when complete, the output
".-
...,.-
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.'
•,
•
-,
:
~".
~. ."
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•
.' ."' .
.-
.
•
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Data PCbase '"' 1Tr
't..••~. -- >
."~, ..,
'--.- I~
,
PC ;.: .' .;' PC ..~c#2" #3 ..# 4
;::'..
""•
"
-"
.•
,
.'
Ccnt:-al i::.ed databa::o:e for a nC't,vo:-k<Glf r.l.lcrocomputers.
.. '
..'..
,
"
.. .,
'.
", , ",
.......
, ,
..
. . 5
" -ava11a'c'le~ for 'thll't' segllle'n't·, 'to~ '. ' ~ .' '.. .' .'
'the' r'ainfall/run'off module
"
"
18
,.~o,,1;roi p!' ano'ther user),' A...'. .; , .. ~
. ~ '.. . ......'. ~. . .for year 1979 ...hile' rainfall/runof!' ,TS. .' .' '-. '. . - .•. ~
..TS is,processed
:. "
.........precipi'ta't-ion
, -; ......p,rocess,ed up 't.o year , 978', -the 'transport ne't¥or1< ·is p~ocl'fJsed up 'tp 1977,
; . ..} ". , .,.
'the se"'ag~ 'trea'tmen't ~~an't processi~g u~ 'to ye~r 1976, .and.'the'disp~rsion: • . '.. " 'e' ~ • • • . ' '. •. ,
of .'tlle resul -tinll; pollu'tan'ts in. 'tl!.e receiving ...i'ters 'up 'to "year' 975; all-. .- .
; '", . .... .'.. (per~i'Ps under ••'the
,'..~.
.:-'.",. ...
.,,,'
" .
" .
"j~ .; t
..of -tohis processing occUl'ing. . ~. . .concurrently..'
, ,
, .~: Iden'tifica'tion of solu'tions
Con'tinlJous mod.el}ing using a large urban s'torm ...a'ter package like
.' '.SWMM3 "in a sequential time-sharing comp~t1ng env1ronment~ c~~ates tvo
significan't problelllll,: ,") i't makes manual managemen't o'f ,I/O TS da'ta
.vir'tually impassible 2) a ~on cost-effective
..
compu'ting process. ·Solu'tion8. 'to 'these problems lie in 'the selec'ted
,application of recen~ advances in computer technolo~ to co~putat1onal
hydrology, .-A specially adap'ted, appliCa'tion-Or1~n'tedDBMS ...hich provides easy
.-acces~ 'to TS da'ta, independen't of de~ai~c of ~'to.age'c~ r~duce the I/O
continuous TS recordc efficien'tly.
data management problem. The DBMS mus't
... "
-resolution
, .Computing efficiency CL~ be e1gn1f1c~tly improved by ~r~piac1ng>
sequen'tial processing ...i'th parallel p.oceesing.•~ !
~'
in ...hich' . independen't
portions o! a large package execute.concurrently in a 'properly linked.' ,
config~~tion of PC's.'- ....
Note that concurrent processing c~~ ~also be
.'achieved in a cainframe environment using cUlti-u~e~ fea~ures. but-that a
-,',-• PC net~ork is in~erentli core r~liable.
:---.--...
~:
"