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Resource Allocation with Dependencies in Business Process Management Systems

Abstract

Business Process Management Systems (BPMS) facilitate the execution of business processes by coordinating all involved resources. Traditional BPMS assume that these resources are independent from one another, which justifies a greedy allocation strategy of offering each work item as soon as it becomes available. In this paper, we develop a formal technique to derive an optimal schedule for work items that have dependencies and resource conflicts. We build our work on Answer Set Programming (ASP), which is supported by a wide range of efficient solvers. We apply our technique in an industry scenario and evaluate its effectiveness. In this way, we contribute an explicit notion of resource dependencies within BPMS research and a technique to derive optimal schedules.

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Resource Allocation with Dependencies in Business Process Management Systems

Author: Havur, Giray; Cabanillas Macías, Cristina; Mendling, Jan; Polleres, Axel
Publisher: Springer
Year: 2016
DOI: 10.1007/978-3-319-45468-9_1
Source: https://idus.us.es/bitstreams/2015f5db-c9d1-4f1b-91e8-51fbf1dc5a80/download
Resou ce Alloca ion wi h Dependencies
in Business P ocess Managemen Sys ems
Gi ay Ha u , C is ina Cabanillas, Jan Mendling, and Axel Polle es
Vienna Uni e si y o Economics and Business, Vienna, Aus ia
{gi ay.ha u ,c is ina.cabanillas,jan.mendling,axel.polle es}@wu.ac.a
Abs ac . Business P ocess Managemen Sys ems (BPMS) acili a e
he execu ion o business p ocesses by coo dina ing all in ol ed esou ces.
T adi ional BPMS assume ha hese esou ces a e independen om one
ano he , which jus ifies a g eedy alloca ion s a egy o offe ing each wo k
i em as soon as i becomes a ailable. In his pape , we de elop a o -
mal echnique o de i e an op imal schedule o wo k i ems ha ha e
dependencies and esou ce con lic s. We build ou wo k on Answe Se
P og amming (ASP), which is suppo ed by a wide ange o efficien
sol e s. We apply ou echnique in an indus y scena io and e alua e i s
effec i eness. In his way, we con ibu e an explici no ion o esou ce
dependencies wi hin BPMS esea ch and a echnique o de i e op imal
schedules.
Keywo ds: Answe Se P og amming ·Op imali y ·Resou ce
alloca ion ·Resou ce equi emen s ·Wo k scheduling
1 In oduc ion
Business P ocess Managemen Sys ems (BPMS) ha e been designed as an in e-
g al pa o he business p ocess managemen (BPM) li ecycle by coo dina ing
all esou ces in ol ed in a p ocess including people, machines and sys ems [1].
A design ime, BPMS ake as inpu a business p ocess model en iched wi h
echnical de ails such as ole assignmen s, da a p ocessing and sys em in e aces
as a specifica ion o he execu ion o a ious p ocess ins ances. In his way, hey
suppo he efficien and effec i e execu ion o business p ocesses [2].
I is an implici assump ion o BPMS ha wo k i ems a e independen om
one ano he . I his assump ion holds, i is fine o pu wo k i ems in a queue and
offe hem o a ailable esou ces igh away. This app oach o esou ce alloca-
ion, can be summa ized as a g eedy s a egy. Howe e , i he e a e dependencies
be ween wo k i ems, his s a egy can easily become subop imal. Some domains
like enginee ing o heal hca e ha e a ich se o ac i i ies o which a ious
Funded by he Aus ian Resea ch P omo ion Agency (FFG) g an 845638 (SHAPE).
esou ces, human and non-human, a e equi ed a he same ime. Resou ce con-
flic s ha e o en he consequence ha wo king on one wo k i em blocks esou ces
such ha o he wo k i ems canno be wo ked on. This obse a ion emphasizes
he need o echniques o make be e use o exis ing esou ces in business
p ocesses [3].
In his pape , we add ess cu en limi a ions o BPMS wi h espec o aking
such esou ce cons ain s in o accoun . We ex end p io esea ch on he in e-
g a ion o BPMS wi h calenda s [4] o ake dependencies and esou ce conflic s
be ween wo k i ems in o accoun . We de elop a echnique o speci ying hese
dependencies in a o mal way in o de o de i e a globally op imal schedule o
all esou ces oge he . We define ou echnique using Answe Se P og amming
(ASP), a o malism om logic p og amming ha has been ound o scale well
o sol ing p oblems as he one we ackle [5]. We e alua e ou echnique using
an indus y scena io om he ailway enginee ing domain. Ou con ibu ion o
esea ch on BPMS is an explici no ion o dependence along wi h a echnique o
achie e an op imal schedule.
The pape is s uc u ed as ollows. Sec ion 2p esen s and analyzes an indus-
y scena io. Sec ion 3concep ually desc ibes he esou ce alloca ion p oblem.
Sec ion 4explains ou ASP-based solu ion and how i can be applied o he
indus y scena io. Sec ion 5e alua es he solu ion. Sec ion 6discusses ela ed
wo k. Sec ion 7summa izes he conclusions o he wo k and he u u e s eps.
2 Mo i a ion
In he ollowing, we desc ibe an indus y scena io ha leads us o a mo e de ailed
defini ion o he esou ce alloca ion p oblem and i s complexi y.
2.1 Indus y Scena io
A company ha p o ides la ge-scale echnical in as uc u e o ailway au oma-
ion equi es igo ous es ing o he sys ems deployed. Each sys em consis s o
diffe en ypes and numbe o ha dwa e ha a e fi s se up in a labo a o y. This
se up is execu ed by some employees specialized in diffe en ypes o ha dwa e.
A e wa ds, he simula ion is un unde supe ision.
Figu e 1depic s wo p ocess models ep esen ing he se up and un phases
o wo es s. We use ( imed) Pe i ne s [6] o ep esen ing he p ocesses. The
p ocess ac i i ies a e ep esen ed by ansi ions (ai). The numbe wi hin squa e
b acke s nex o he ac i i ies indica es hei (de aul maximum) du a ion in
gene ic ime uni s (TU). The numbe s unde p ocess names indica e he s a -
ing imes o he p ocess execu ions: 8 TU o Tes -1 and 12 TU o Tes -2.
The p ocesses a e simila o all he es ing p ojec s bu diffe in he ac i i ies
equi ed o se ing up he ha dwa e as well as in he esou ce equi emen s asso-
cia ed wi h hem. Ce ain esou ces can only be alloca ed o ac i i ies du ing
wo king pe iods, i.e., we wan o en o ce ime in e als (so called b eaks) whe e
Fig. 1. Wo kflow o wo p ojec s
some esou ces a e no a ailable. In ou scena io, no esou ce is a ailable in he
in e als [0,8), [19,32), [43,56), and [67,80).
Fo comple ing es s, he a ailable non-human esou ces in he o ganiza ion
include 13 uni s o space dis ibu ed in o 2 labo a o ies (Table 1) and se e al
uni s o 3 ypes o ha dwa e (Table 2). The human esou ces o he company
a e specialized in he execu ion o specific phases o he wo es ing p ojec s,
whose ac i i ies a e able o comple e in a specific ime. Table 3shows a ailable
esou ces in diffe en p ocess phases and he e o e, hei abili y o conduc ce -
ain ac i i ies along wi h hei yea s o expe ience in he company in squa e
b acke s.
The equi emen s on he use o such esou ces in he p ocess ac i i ies a e
showninTable4. Each p ocess ac i i y equi es a specific se o esou ces o i s
comple ion. Fo ins ance, h ee o he ac i i ies in ol ed in he se up o Tes -1
equi e 1 employee wo king on 1 uni o he ha dwa e HW-1 in a labo a o y; 1
se up ac i i y equi es 1 employee wo king on 1 uni o he ha dwa e HW-2 in
a labo a o y; and he un ac i i y equi es 4 employees. Besides, a es can only
be execu ed i he whole se up akes place in he same labo a o y.
The aim in his scena io is o op imize he o e all execu ion ime o simul-
aneous es s and consequen ly, he space usage in he labo a o ies.
2.2 Insigh s
The esou ce alloca ion p oblem1deals wi h he assignmen o esou ces and
ime in e als o he execu ion o ac i i ies. The complexi y o esou ce allo-
ca ion in BPM a ises om coo dina ing he explici and implici dependencies
1Commonly e e ed as scheduling.
ac oss a b oad se o esou ces and ac i i ies o p ocesses as well as om sol ing
po en ial conflic s on he use o ce ain esou ces. As we obse e in ou indus y
scena io, such dependencies include, among o he s: (i) esou ce equi emen s,
i.e., he cha ac e is ics o he esou ces ha a e in ol ed in an ac i i y (e.g.,
oles o skills) (c . Table 3); (ii) empo al equi emen s. Fo ins ance, he du a-
ion o he ac i i ies may be s a ic o may depend on he cha ac e is ics o he
se o esou ces in ol ed in i , especially o collabo a i e ac i i ies in which se -
e al employees wo k oge he (such as o he ac i i ies o he un phase o a
es ing p ocess). Fu he mo e, esou ce a ailabili y may no be unlimi ed (e.g.,
b eak calenda s). In addi ion, esou ce conflic s may eme ge om in e depen-
dencies be ween equi emen s, e.g., ac i i ies migh need o be execu ed wi hin
a specific se ing which may be associa ed wi h (o sha e esou ces wi h) he
se ing o o he ac i i ies (e.g., all he se up ac i i ies o a es ing p ocess mus
be pe o med in he same labo a o y).
A esou ce alloca ion is easible i (1) ac i i ies a e scheduled wi h espec o
ime cons ain s de i ed om ac i i y du a ions and con ol flow o he p ocess
model, and (2) esou ces a e alloca ed o scheduled ac i i ies in acco dance wi h
esou ce a ailabili y and esou ce equi emen s o ac i i ies. This combina o-
ial p oblem o finding a easible esou ce alloca ion unde cons ain s is an
NP-Comple e p oblem [7]. Howe e , o ganiza ions gene ally pu sue an op imal
alloca ion o esou ces o p ocess ac i i ies aiming a minimizing o e all exe-
cu ion imes o cos s, o maximizing he usage o he esou ces a ailable. In
p esence o objec i e unc ions he esou ce alloca ion p oblem becomes ΔP
2[8].
3 Concep ualiza ion o he Resou ce Alloca ion P oblem
Figu e 2illus a es ou concep ualiza ion o he esou ce alloca ion p oblem. We
di ide i in o h ee complexi y laye s ela ed o he a o emen ioned dependencies
and esou ce conflic s. Op imiza ion unc ions can be applied o all ypes o allo-
ca ion p oblems. This model has been defined om he cha ac e is ics iden ified
in ou indus y scena io as well as in ela ed li e a u e [9].
Table 1. A ailable space in labs
LAB −1LAB −2
Space 4 9
Table 2. A ailable ha dwa e (HW)
Type Uni s
HW1 hw1a, hw1b, hw1c
HW2 hw2a, hw2b, hw2c, hw2d
HW3 hw3a, hw3b, hw3c
Table 3. Specializa ion o employees
Tes −1Tes −2
Se up Run Se up Run
Glen[7]  
D ew[7] 
E an[3] 
Ma y[5]  
Ka e[6]  
Amy[8]   
Table 4. Ac i i y equi emen s
Ac i i ies Requi emen s
Tes -1 a1−a31Employee:Se up-1, 1 Ha dwa e:HW-1, 1 Lab:a1-a4same lab
a41Employee:Se up-1, 1 Ha dwa e :HW-2, 1 Lab:a1-a4same lab
a54Employee:Run-1, a e execu ion(a.e.) elease he lab o a1-a4
Tes -2 a6−a81Employee:Se up-2, 1 Ha dwa e:HW-2, 1 Lab:a6-a11 same lab
a9−a11 1Employee:Se up-2, 1 Ha dwa e :HW-3, 1 Lab:a6-a11 same lab
a12 2Employee:Run-2 (hasExp>5), a.e. elease he lab o a6-a11
Fig. 2. Resou ce alloca ion in business p ocesses
Fig. 3. Resou ce on ology and example ins an ia ion

3.1 Basic Resou ce Alloca ion
Th ee elemen s a e in ol ed in a basic esou ce alloca ion, namely: a model ha
s o es all he in o ma ion equi ed abou he esou ces a ailable, in o ma ion
abou he expec ed du a ion o he p ocess ac i i ies, and a language o defining
he es ic ions ha cha ac e ize he alloca ion.
Resou ce On ology. As a uni o m and s anda dized ep esen a ion language,
we sugges he use o RDF Schema (RDFS) [10] o model o ganiza ional in o -
ma ion and esou ces. Figu e 3illus a es a sample RDFS on ology, in which
a esou ce is cha ac e ized by a ype and can ha e one o mo e a ibu es.
In pa icula , any esou ce ype (e.g. Employee) is a subclass o d s:Resou ce.
The a ibu es a e all o ype d :P ope y; domain ( d s:domain) and ange o
a ibu es a e indica ed wi h s aigh a ows labeled wi h he a ibu e name,
whe eas dashed a ows indica e an d s:subclassO . The e a e h ee diffe en ypes
o esou ces: Employee,Ha dwa e and Lab, whe e Ha dwa e has h ee esou ce
sub ypes. Employees ha e a ibu es o hei name (hasName), ole(s) (has-
Role) and expe ience le el (hasExp) in he o ganiza ion (numbe o yea s). Labs
p o ide a ce ain amoun o space o expe imen s (hasSpace). An ins an ia ion
o he on ology is desc ibed a he bo om o he figu e using he RDF Tu -
le syn ax [11]. This ins an ia ion ep esen s Tables 1,2and 3o he indus y
scena io.
Ac i i y Du a ion. Resou ce alloca ion aims a p ope ly dis ibu ing a ail-
able esou ces among unning and coming wo k i ems. The main empo al aspec
is de e mined by he expec ed du a ion o he ac i i ies. The du a ion can be
p edefined acco ding o he ype o ac i i y o calcula ed om p e ious execu-
ions, usually aking he a e age du a ion as e e ence. This in o ma ion can be
included in he execu able p ocess model as a p ope y o an ac i i y (e.g. wi h
BPMN [12]) o can be modelled ex e nally. In ei he case, i has o be accessible
by he alloca ion algo i hm.
Resou ce Alloca ion. Resou ce alloca ion can be seen as a wo-s ep defini ion
o es ic ions. Fi s , he so-called esou ce assignmen s mus be defined, i.e., he
es ic ions ha de e mine which esou ces can be in ol ed in he ac i i ies [13]
acco ding o hei p ope ies. The ou come o esou ce assignmen is one o
mo e2 esou ce se s wi h he se o esou ces ha can be po en ially alloca ed o
an ac i i y a un ime. The second s ep assigns ca dinali y o he esou ce se s
such ha diffe en se ings can be desc ibed, e.g. o he execu ion o ac i i y
a1, 1 employee wi h ole se up-1, 1 ha dwa e o ype HW2, and 1 uni space o
a labo a o y a e equi ed.
The e exis languages o assigning esou ce se s o p ocess ac i i ies [13–
16]. Howe e , ca dinali y is gene ally dis ega ded unde he assump ion ha
2Since se e al se s o es ic ions can be p o ided, e.g. o ac i i y a1 esou ces wi h
ei he ole 1o skill s1a e equi ed.
only one esou ce will be alloca ed o each p ocess ac i i y. This is a limi a ion
o cu en BPMS ha p e en s he implemen a ion o indus y scena ios like he
one desc ibed in Sec . 2.1.
3.2 Ad anced Time Managemen
This laye ex ends he empo al aspec o esou ce alloca ion by aking in o
accoun ha : (i) esou ce a ailabili y affec s alloca ion, and ha (ii) he esou ce
se s alloca ed o an ac i i y may affec i s du a ion. Rega ding esou ce a ail-
abili y, calenda s a e an effec i e way o speci ying diffe en esou ce a ailabili y
s a us, such as a ailable, una ailable, occupied/busy o blocked [9]. Such in o -
ma ion mus be accessible by he esou ce alloca ion module. As o he a iable
ac i i y du a ions depending o he esou ce alloca ion, h ee specifici y le els
can be dis inguished:
–Resou ce-se -based du a ion, i.e., a iple (ac i i y, esou ceSe , du a ion)
s a ing he (minimum/a e age) amoun o ime ha i akes o he esou ces
wi hin a specific esou ce se (i.e., ca dinali y is dis ega ded) o execu e
ins ances o a ce ain ac i i y. Fo ins ance, (a1, echnician, 6) specifies ha
people wi h he ole echnician need (a leas /on a e age) 6 TU o comple e
ac i i y a1, assuming ha echnician is an o ganisa ional ole.
–Resou ce-based du a ion, i.e., a iple (ac i i y, esou ce, du a ion) s a ing
he (minimum/a e age) amoun o ime ha i akes o a conc e e esou ce
o execu e ins ances o a ce ain ac i i y. Fo ins ance, (a1,John,8) specifies
ha John needs (a leas /on a e age) 8 TU o comple e ac i i y a1.
–Agg ega ion-based du a ion, i.e., a iple (ac i i y, g oup, du a ion) s a ing
he (minimum/a e age) amoun o ime ha i akes o a specific g oup o
execu e ins ances o a ce ain ac i i y. In his pape , we use g oup o e e
o a se o human esou ces ha wo k oge he in he comple ion o a wo k
i em, i.e., ca dinali y is conside ed. The e o e, a g oup migh be composed
o esou ces om diffe en esou ce se s which may no necessa ily sha e a
specific esou ce-se -based du a ion. An agg ega ion unc ion mus be imple-
men ed in o de o de i e he mos app op ia e du a ion o an ac i i y when
a g oup is alloca ed o i . The defini ion o ha unc ion is up o he o ganiza-
ion. Fo ins ance, a g oup migh be composed o (John,Clai e), whe e John
has an associa ed du a ion o 8 TU o ac i i y a1and Clai e does no ha e a
specific du a ion bu she has ole echnician, wi h an associa ed du a ion o
6 TU o ac i i y a1. S a egies o alloca ing he g oup o he ac i i y could
be o conside he maximum ime needed o he esou ces in ol ed (i.e., 8
TU), o o conside he mean o all he du a ions (i.e., 7 TU) assuming ha
he join wo k o wo people will be as e han one single esou ce comple ing
all he wo k.
3.3 Ad anced Resou ce Managemen
The basic esou ce alloca ion laye conside s esou ces o be disc e e, i.e. hey
a e ei he ully a ailable o ully busy/occupied. This applies o many ypes o
esou ces, e.g. people, so wa e o ha dwa e. Howe e , o ce ain ypes o non-
human esou ces, a ailabili y can be pa ial a a specific poin in ime. Mo eo e ,
hey may ha e o he fluen a ibu es. Fo ins ance, cumula i e esou ces a e
hence cha ac e ized by hei dynamic a ibu es and hey can be alloca ed o
mo e han one ac i i y a a ime, e.g. in Fig. 2 he e is a esou ce oom 1 whose
occupancy changes o e ime.
We use he ASP sol e clasp [17] due o i s efficiency o ou expe imen s. This
allows us o use in ege a iables as a ibu es. The e a e also o he ex ensions
o ASP such as FASP [18] ha adds he powe o model con inuous a iables.
3.4 Op imiza ion Func ion
Sea ching o ( he exis ence o ) a easible esou ce alloca ion ensu es ha all he
wo k i ems can e en ually be comple ed wi h he a ailable esou ces. Howe e ,
ypically schedules should also ulfill some kind o op imali y c i e ion, mos
commonly comple ion o he schedule in he sho es possible o e all ime. O he
op imiza ion c i e ia may in ol e o ins ance cos s o he alloca ion o ce ain
esou ces o pa icula ac i i ies, e c.
Gi en such an op imiza ion c i e ion, he e a e g eedy app oaches [19]p o-
iding a subs an ial imp o emen s o e choosing any easible schedule, al hough
such echniques depend on heu is ics and may no find a globally op imal solu-
ion o complex alloca ion p oblems.
We e e o [20] o u he in o ma ion on a ious op imiza ion unc ions,
bu emphasize ha ou app oach will in p inciple allow a bi a y op imiza ion
unc ions and finds op imal solu ions – simila in spi i o encodings o cos
op imal planning using ASP [21].
4 Implemen a ion wi h ASP
Answe Se P og amming (ASP) [17] is a decla a i e (logic-p og amming-s yle)
pa adigm. I s exp essi e ep esen a ion language, ease o use, and compu a ional
effec i eness acili a e he implemen a ion o combina o ial sea ch and op imiza-
ion p oblems (p ima ily NP-ha d). Modi ying, efining, and ex ending an ASP
p og am is uncomplica ed due o i s s ong decla a i e aspec .
An ASP p og am Πis a fini e se o ules o he o m:
A0←A1,...,A
m,no A
m+1,...,no A
n.(1)
whe e n≥m≥0 and each Ai∈σa e ( unc ion- ee fi s -o de ) a oms; i A0is
emp y in a ule , we call a cons ain , and i n=m= 0 we call a ac .
Whene e Aiis a fi s -o de p edica e wi h a iables wi hin a ule o he
o m (1), his ule is conside ed as a sho cu o i s g ounding g ound( ), i.e.,
he se o i s g ound ins an ia ions ob ained by eplacing he a iables wi h all
possible cons an s occu ing in Π. Likewise, we deno e by g ound(Π) he se
o ules ob ained om g ounding all ules in Π. Se s o ules a e e alua ed in
ASP unde he so-called s able-model seman ics, which allows se e al models,
so called answe se s (c . [22] o de ails).
ASP Sol e s ypically fi s compu e a subse o g ound(Π) and hen use
a DPLL-like b anch and bound algo i hm o find answe se s o his g ound
p og am. We use he ASP sol e clasp [17] o ou expe imen s as i has p o ed
o be one o he mos efficien implemen a ions a ailable [23].
As syn ac ic ex ension, in place o a oms, clasp allows se -like
choice exp essions o he o m E={A1,...,A
k}which a e ue o any sub-
se o E; ha is, when used in heads o ules, Egene a es many answe se s,
and such ules a e o en e e ed o as choice ules. Ano he ex ension suppo ed
in clasp a e op imiza ion s a emen s [17] o indica e p e e ences be ween possible
answe se s:
#minimize{A1:Body1=w1,...,A
m:Bodym=wm@p}
associa es in ege weigh s (de aul ing o 1) wi h a oms Ai(condi ional o Bodyi
being ue), whe e such a s a emen exp esses ha we wan o find only answe
se s wi h he smalles agg ega ed weigh sum; again, a iables in Ai:Bodyi=wi
a e eplaced a g ounding w. . . all possible ins an ia ions. Se e al op imiza ion
s a emen s can be in oduced by assigning he s a emen a p io i y le el p. Rea-
soning p oblems including such weak cons ain s a e ΔP
2-comple e.
Finally, many p oblems con en ien ly modelled in ASP equi e a bounda y
pa ame e k ha eflec s he size o he solu ion. Howe e , o en in p oblems like
planning o model checking his bounda y (e.g. he plan leng h) is no known
up on , and he e o e such p oblems a e add essed by conside ing one p oblem
ins ance a e ano he while g adually inc easing his pa ame e k. Re-p ocessing
epea edly he en i e p oblem is a edundan app oach, which is why inc emen-
al ASP (iASP) [17] na i ely suppo s inc emen al compu a ion o answe se s;
he in ui ion is oo ed in ea ing p og ams in p og am slices (ex ensions). In
each inc emen al s ep, a successi e ex ension o he p og am is conside ed whe e
p e ious compu a ions a e e-used as a as possible.
A o me e sion o ou echnique is de ailed in [5]. We enhance ou encoding
in h ee olds: (1) basic esou ce alloca ion suppo ing mul iple business p ocesses
wi h mul iple unning ins ances, (2) defini ion o ad anced esou ce managemen
concep s, and (3) defini ion o ad anced ime managemen concep s. The en i e
ASP encoding can be ound a h p://goo.gl/Q7B2 4.
4.1 Basic Resou ce Alloca ion
This p og am schedules he ac i i ies in business p ocesses desc ibed as imed
Pe i ne s (c . he gene ic o mula ion o 1-sa e Pe i Ne s [5, Sec . 4]) and allo-
ca es esou ces o ac i i ies wi h espec o ac i i y- esou ce equi emen s. To
achie e his, he p og am finds a fi ing sequence be ween ini ial and goal places
o gi en p ocesses, schedules he ac i i ies in be ween, and alloca es esou ces
by complying wi h esou ce equi emen s. In ou p og am, a fi ing sequence is
ep esen ed as p edica es i e(a,b,i,k), which means ha an ac i i y ao a
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