PERT/CPM ITS APPLICATION TO LIBRARY ANDINFORMATION SYSTEMS

. Introduces ~he PERT/CPM (Netwoyk Analysis) tech-n'Ul~s.and ~Zains the methodology of their appli-eatrion, Apphes CPM technique for planning andscheduling publication of an cWstivtcting service.Suggests other aYea8 of application of PERT/CRMtechniques in Zibrary.and information works. Conclud-es t~t Ne~rk AnaZysi~ is applicabZe to libraryand ~nformat~on works ~th a few exceptions likereference service.

1. INTRODUCTION

In order to solve the problems and to aidthe planning of library and information works,various te chn lque » have been used, e.g. flowcharting. Prograznrne (or Performance) Evalua-tion and Review Technique (PERT) is used as aplanning and control t echn ique to expedite success-ful completion of any project or programme. Itis a modification of milestone budgeting and it usesa time -ev enr network analys is. PERT can handleuncertainty, and hall the capacity for predictionand simulation.

Critical Path Method (CPM) is a!.SO a plan-ning and control" technique but is used whereinthere is certainty of time schedule, e. g. publi-cation of an abstract bulletin. It places moreemphasis on optimum utilisation of resources andreduction in ~erall cost. A delay in any taskalong this path would ne ce s aa r lly delay completionof the p ro jec t ,

Thus PERT /CPM or Network Analysis maybe described as a group of techniques for present-ing information relating time and resources so asto assist in analysing, planning, scheduling, andcontrolling projects/programmes. With the helpof PERT /CPM, it ill possible to follow the actualprogress of the project and evaluate the proposedalternatives with respect to cost and time.

Z. ELEMENTS OF PERTjCPM OR NETWORKANALYSIS

Z. I Activity - An activity is a clearly definableportion of a project, which could be an operation,

Vol Z5 No 1-4 Mar-Dec 1978

M.K.DHIRENDRA RAOplanning & LLailum D;WisionNational Physical LaboratoryNew Delhi~llOOlZ

a process or a situation consuming time andnormally other resources. It lies between twoevents.

Z.2 Events mark the completion of one or aeve ralactivities at a given point of t irne .

Z. 2. 1 Start 'Event - An event with succeed ing butno prec ed ing act iv it ie s ,

Z. 2. 2 End Event - An event. VI ith preced ing but .,.0

succeeding activities.

2.3 Dummy Activities - An activity wh teh r epze-sents only an int e rd epend encv and does not con-sume either resources or t irn e . In ot.her words,when an activity on one pat r- 'cannot he .started'until the completion of another a(;tivity on a

.different path, the completion. ev ent of the 'mustbe completed' activity is jc ined by II d.'~mmyactivity to the starting eveut of the 'cannot bestarted' activity.

Logical relationships between activitiescan now be representee! all.·folluwtl:

a) In F ig. I, act iv ity cmay be started onthe completion ofactivitles A and B.

b) In Fig. Z, activ it iesB and C may bestarted on thecornplet ion ofactivity A.

c) In Fig. 3, activitiesBand C may startafter the complet ionof Activity A.

Activity D canstart after thecomplet ion ofactivities B and c.

31

DHIRENDRA RAO

2.4 Critical Path is the path traced by a conti-nuous chain of critical activities from the startevent to finish event; such that the sum of theactivlty durations is largest compared to other'Paths.

.s

F===~,r=========~~7

~t---"'----~

Fig.4

There are 3 paths inFig.4.

1- 2, 2-5, 5 -7 11 days

II 1- 3, 3-7 15 days

III 1-4, 4-6, 6 -7 12 days

II is the c rit ic al path and project durationis 15 days.

Activities on critical path are calledcritical activities and they govern the projectduration.

In a network, there may be more than onecritical path. The paths other than critical pathare called as alack paths. The term 'Slack'pertains to events only and may be negative.

2.5 Schedul in& - The process of an igningcalendar dates to various event timings in thenetwork.

2.6 Crashing - In many projects the estimatedproject duration may be more than the targetduration, in which case it is required to comp re s sthe critical path/s to achieve the target duration.

Crashing is also done to offset the indirectcosts like supervisory cost, capital cost, penalties,etc. which rises with time.

2.7 Updating - The process of periodic reviewing,reallocating resources where necessary, an .redraft ing the network, when the project is inactual progress.

For completed activities the time ls takenas zero, for activities in progress the time re-maining is taken and for other activities the latestestimate value is substituted.

Terms

3. RULES AND SYMBOLS USED IN NETWORK ANALYSIS

~xplanatory Remarks

l. Optimis tic time

2. Pessimistic time estimate

3. Most likely time estimate

4. Expected activity time

5.

6.

Earliest event

Latest event time

a

b

m

tIel or te

T(E) or TE

T(Ll or TL XATC I

While rendering,t(el, T(E), and T(Llhas been adopted forease of typing

7. Actual time of completion

J. aULEI NoII1 SYWIIOLI USED IN "rrwoaK ANALYSII . C_ot.

Ito. Torm Iymbol

.. Acttvity

~. •• pruetltattonof eve"l.

10. -------- ....II

32

ExplanOLtory R.emarka

Time flow. from the taU to the head 9f tM II'row Thel_.h.net direction of the ar r ow have ,,0 •••• Ule •• c. alther, •• o.a~phlcaUv or in terma of Ume The eam. WIlt of tl~ .ho ••.•be ueed thr oughout the "_work.

Evente are l'''I' ••• t.4 by nWllber ••P • S .t •••.••for pr~.din. and euce •• eIllll no••••••.

Can alee. b. deplct,.d by .ubl.lln. 01' •••• U.ctlve c •••••

Ann Llb Sei Doc

T (f) -t- 'IL) 1.oft·••..,,_.- .h•••• 11•••• v ••••••••• $l..'P' ••."•..•..the lat •••• v.t tim •• TIL). _<I~ c Bottom aeament _. the ¥"tual tlm • ., campi ••••• of U••8-- event. ATe

Feference ~o I:the urne event nbln In four aeame,.. ia. tile t. lull

r--.",..-...,..--'" In other net .•..ork. leament waul' b•••••••• for·~•• "t.

P£RT/CPM

u.

13. Interface event

14. MUutone event

15. ~\ft1berlu. ofevent,

4. PROCEDURE FOR DEVELOPING' A NETWORKPLAN

A network plan is a diagramatic r ep r e senta>tion of the activities which must be undertaken andcompleted for carrying out a project.

The first step in network systems is todef ine clearly and unarnb iguously the goals to bereached. We must, therefore answer the followingquestions with a statement of premises.

al What are the project objectives?

b) What are the major activities of thework to be performed, and their re-lationships?

c) How will be the division of work/respons ibilit ies?

d) What resources, i,e. men, material,and/or machinery is available orrequired?

e) What are the likely lnform at Ion re-quirements of the var ious types andlevels of management to be 'involved inthe project?

Once these are set, then the network can beconstructed, based on the logical.relationshipsbetween the various tasks.

The following steps ~y be followed whiledrawing a network plan.

4.1 List separately all the activities of the project.

4.2 Indicate the immediately preceding andsucceeding activities.

4.3 The next step is to draw the network whichportrays each of these activities.

While drawing the network:

V()l 25 No 1-4 Mar-Dee 1978

All lucceedln. eventl of •• tven ,wee.41n •••••• h••••be numbered aerially from top to t.ottom .• \lCe •••••

event. h.v~ a Maher numb •. thar tIl.&r ,..ece4 •••••••••.

4.3. I Group the act Ivit les in order of Precedence.

4.3.2 All those activities Which should occursimultaeeously at any given instant should be puttogether.

4.3.3 Different processes should be arranged. inthe natur al order in which they should occur.

4.4 Rearrange the activities in such a way thatthe network appearance improves, for example,see that unnecessary dummies are eliminated.

4.5 Estimate the time and resources required foreach activity.

4.6 Calculate the critlcal path.

In brief, in the PERT /CPM technique theprojects are broken down to individual events andactivities and arranged in a logical network.These individual activities are then given timeestimates for the ir execut ion.

5. ACTIVITY TIME ESTIMATE

There are two distinct systems of estimat-ing activity duration. In single time estimate,which is used in CPM, the estimates are basedon the past experience and averaging the timevalues from past records.

In 3-time estimate, for every activity, thetime is estimated under three assumed situations.

The 3 Urnes are -

1. Optimist ic time (al: It is a~ estimate of theminimum time an activity will take, when every-thing goes right the first time.

2. Pessimistic time (b): It is an estimate ofmaximum time an activity will take - a resultwhich would occu-r und er adverse conditions.

/

DmRENDRA RAO

3. Most likely time (rn) : It is an estimate ofthe normal time an activity will take, a resultwhich would occur most often if the activity couldbe repeated many times under similar c ircum-stances.

Activity Duration' or 'Expected ActivityT Ime' is the time which an act ivity is pred icted torequire for its completion. It is denoted by tIe) or

te'

There are two distinct systems of estimat-ing Activity Duration.

In 'Single time estimate' this would be thesame as the 'Most likely time', m.

The expected time for the activity under the'Three time estimate' is given by the formula:

tIe) a + 4m + b6

3-time estimate is used in PERT.

5.2 Calculation of Earliest event time, T(E)

It is the earliest possible time at which anevent can occur.

In analys ing a network, the earliest eventtimes for all the events in the network should becalculated first·proceeding from the start eventto the end event.

If there is only one activity preceding anevent, the calculation of its earliest event time isstraight forward:

Earliest event time of preced ing event +estimate for the activity inbetween.

This set of calulations is called the For-ward Pass.

When an event is preceded by severalactivities, consider all the activities merging intoan event node.

. II, 18, 15 & 14 are theearliest event times,T(E) , of events 1,2,3 &: 4 respectively.

Fig.5

Event 5 in the Fig. 5 c an take placeearliest on:

the 16th day be cuaae of activity Athe 20th day because of activity Bthe 21st day because of activity Cthe 23rd day because of activity D

But since event 5 does not occur unt U allthe four activities A, B, C and D are completed,event 5 can occur earliest on the 23rd day.

Thus, the earliest event time, T(E), isequal to the maximum of all the totals of theearliest event time of the preced ing event and thetime required for the activity inbetween.

5.3 Calculation of latest event time T(L)

It is the latest poss ible time at which anevent should occur so that the targeted projectdurat ion is not exceeded.

The latest event times in a network arecalculated backwards starting from the end eventand asking for each preced ing event the question -what is the latest time the preceding event canoccur, once the latest event time for the succeed-ing event is known?

Tha latest event time for the end event isthe same as the earliest event time calculatedfor it.

If the re- is only one activity flowing out froman event, its latel!t time calculation ill straight-forward:

Latest event time of the succeedingevent - time est imate for the activityi$etween.

If there are several act lv lt ies flowing outfrom an event, its latest event time rnuat be cal-culated backwards from the viewpoint of each suchactivity.

Fig. 6

Event 5 in the F ii.' 6 mullt take placelatellt on: .

the 35th day because of activity Ethe 33rd day bec ause of actlvlty Fthe 3Znd'day be cauee of activity G

Ann Lib Sel Doc

PERT/CPM

But, since neither event 6, 7 or 8 can bedelayed mo re than the time spec if ied against the m,the event 5 rnuat be c orrrplet ed latest on the 32ndday.

Thus, the latest event time is the rn in irnurnof all the values obtained by taking away the acti-vity times from the latest times correspondingsucceeding events.

The othe r time est imates are Earlieststart time, Earliest finish time, Lat eat f m iaht irne , Lead time, Lag time etc.

5.4 Calculation of Floats:

Float is the play, i. e. the amount of excesst irne , available on any activity. There are tnainlytwo kinds of floats.

5.4. 1 Total Float, (TF)

It is the total expans ion available to anact ivity.

Total float (Latest eventtime ofsucceed ingevent)

(Earliest (Activityevent time - time)of preced ingevent)

L e.T(L) T(E)

. Succeeding event Preceding event) -tf e)

Total float on critical activities is zero,indicating that there is no play available on criticalact iv it ies.

5.4. 2 F re!,.£ 10at (F.:F): It is the amount ofexpansion available without upsetting the subse-quest activities.

Free float = (Earliest eventtime ofsucceedingevent)

(Ear lie stevent timeof preced-ing event)

(Activity- time)

T(E)i. e. Succeeding

event

T(~Precedingevent

-t( e)

The other less commonly occurring Floatsare Independent float, Negative float and Inter-ference float.

The term float pertains to activities only.

6. APPLICATION OF CPM FOR PLANNING ANDSCHEDULING PUBLICATION OF AN ABSTRACTBULLETIN

Envisage a reg ional Documentation Cent rewhich proposes to br ing out a monthly abstract ingae rv ice of documents received by it. Let the

Vol 2S No 1-4 Mar-Dec 1978

various activities in the publication of the abstract-ing service be as under:

1. Receive, scan and select a r-t ic Ie s f r omcurrent documents for abstracting purpose,

2. Note the complete bibliographica1 citationof the documents on standard slip.

3. Prepare abstract on the slip or use authorabstract with suitable modifications, ifnecessary.

4. Conceptually analyse the document andselect subject headings for indexing.

Collect all the abstracts and arrange, underconvenient broad subject headings, alpha-betically by the author's name.

5.

6. Review and check the entries.

7. Ser ialise the entr ie s and prepare the con-tents page.

8. Type rnaste rs of the entr ies and check.After c or r ect ing, release the typed sheetsto printing section for laying out on plates.

9. A1phabetise the author index and subjectindex te rms .

10. Type masters of the indexes and verify.After cor r e ct i.ng, pass on the typed sheetto p r inti.ng section fo r layin~ out.

11. Print copies of the abstract bulletin byphoto-offset printing technique.

12. Collate and bind.

In the CPM network (F ig. 7), the timingsfor the various activities are based on the follow-ing assumptions.

1. Average number of art icles abstracted is500.

2. Number of abstractors are four.

3. Working hours is six hours/day.

4. Rate of preparation of abstracts by oneabstractor is eight/day. Therefore, fourabstractors can abstract 500 articles inabout 15 days. (This includes the time forselection of subject headings for indexingand writing the abstracts on slips. Thisalso assumes that in 70'7. of the cases theabstractor uses the author's abstract withlittle or no modification).

5. Two abstractors can sort 500 ent r Ies andclass ify under broad subject head ings inone day.

DHlR ENDR A R AO

Fl •. t: .J:TWORK ra. PUBLICATION OF AN ABSTRACT BULLETIN

P11I:PARE ASSTR ACTS• SELI:CT SUBIECT soar • CLAIISIFYHEAPINGS E/otTRa:S

t:!S~f.;ln~~--:7:=:-"~"' ,'•...---- .•11(o 15 DaYo 1 Da¥

II. • 0

1. AYOUT MASTERS

or n.TRIES

IIDTE CRITICAL PATH [5 34.5 DayoJ:ARUI:ST EVENT TIME. 15 Dayo IT(E) of EVEIC'T 1]I.ATEST EVE"T TIME = 30 Davo IT(L) OF EVE"1 f>1TOT AL rLOAT • 130.Z8) .ZI .0 ITr OF EVE/otTS 7 AND 51nEE FLOAT. 1(30·Z8) . Zl = 0 IFF OF EVE/otTS 7 AN> 51

6: One person can serlalise the entries byauthor under the broad subject headingsand prepare contents 1ist in two days.

Table I:

7. Typin~ of maste r s of ent r ie s by two typistsfollowed by their verification and correc-tion may take about six dav s ,

EventNo.

8. Laying out of above maste rs may takeabout two days by two pers ons ,

9. Alphabetisation of author index and subjectindex may take about two days by twopersons.

10. Typing of maste r s of indexes by one typis t,their checking and correction may taketwo days.

11. Laying out of indexes by two pe rsons maytake about three hours, i. e .• half a day.

iz. Printing and binding of average 300 copiesof the abstract bulletin may take about twodays by three persons.

Table I summarises the various activitiesin the publication of an abstract bulletin withcorrelponding timings involved.

36

10.

SERIA1.ISE • PREPARECONTENTS PAOI:

Z Daye

NIXT [SSUISTARTS

.0

34·5

Activities and timings involved in thepublication of an abstract bulletin

Activity

1. Prepare abstracts and selectSubject headings

Z. Sort and classify entries

3. Review and check entries

4. Se r ial is e and preparecontents page

5. Type masters of entriesand ve rify

6. Layout masters of entrieson plate s

7. Prepare author and subjectindexes

8. Type masters of indexes

9. Layout indexes on plates

Print copies and bind

ActivityDuration(ind~ __

15

4

Z

6

2

2

2

0.5

2

Ann Lib Sci Doc

6.1 Interpretation of the CPM network

The completed CPM network shows that itwould take thirty four and a half working dayB forpublishing one issue of the abstracting periodical,provided, all the activities, from start to end, takeplace in the required coordination and success ionwithout any delay. It may be noted that the workfor the second issue of the abstracting periodicalcan be started on the twenty first day of the pro-gress of first issue. But, taking into account theregular and other government declared holidaysin an year, increasing growth of contributions,and other unforseeable circumstances, the abstract-ing periodical may reasonably planned to be amonthly service.

6. 2 Monitoring and Evaluation

It is very important that, during the imple-mentation stage, the performance of the variousactivities and the progree s of the work should bemeasured against the CPM network schedules andshortfalls, if any, should be identified and rectified.

7. AREA OF APPLICATION OF PERT/CPM INLIBRARY AND INFORMATION WORKS

al Building and construction work, viz., Newlibrary buildings.

bl Introduction of new services, e. g. SDIservice, translation service etc.

cl Reorganisation of the existing system,e. g. adoption of revised classificationscheme, moving to new building etc.

dl Major repair, overhaul and maintenance,e. g. Computer and reprographic equip-ment.

e) Installation of new equipment or facilities,e. g. installation of computer facility.

fl Miscellaneous preparations of annuallibrary accounts.

Vol Z5 No 1-4 Mar-Dee ,I 978

PERT/eM

8. CONCLUSION

PERT/CPM is a very versatile techniqueavailable for exploitation by information manage,s/executives. PERT/CPM minimises the delays,interruptions and conflicts. These techniques arevery helpful in co-ordinating various jobs of thetotal project and thereby expedite and achievecompletion of project on time. The exampleshown in Sec. 6 proves that PERT /CPM techniqueis applicable to Library and Information works.But, some areas in information science areintangible to PERT/CPM, e.g., reference ser-vice. For large quantum projects, c orrrpute r eanbe employed very effectively.

ACKNOWLEDGEMENT

The author is grateful to Shr l T. N. Rajan,Scientist, INSDOC, and Sh r i R. P. S. Luther,Engineer-in-Charge (PERT), NIDC, for theirhelpful discussions and suggestions.

REFERENCES

[ I) ARCHIBALD (Russel m , VlLLORlA(Richard Ll: Network-based managementsystems (PERT/CPMl. New York, JohnWiley &r. Sons, 1967.

[2) KASHYAP (M M): Network analysis, alibrary project management tool. J. Lib.In!. Sei. 1(2), 1976, 199-231.

[3) SHAFFER (L Rl. RITTER (J Bl, MEYER(W L) : Critical path method. New YorkMcG raw -Hill, 1965. '

[4) WALKER (J R Al:special librar ies .Association, 1966.

Information bulletin inLondon, Library

[5] WIEST (Jedome m , LEVY (Ferdinand K):A management guide to PER T /CPM.Englewood Cliffe, New Jersey, Prentice-Hall, 1969.

37