Realising Dead Path Elimination in BPMN

Transcription

1 Relising De Pth Elimintion in BPMN Mtthis Weilih, Alexner Grosskopf Hsso Plttner Institute Potsm, Germny Alistir Brros SAP Reserh Brisne, Austrli Astrt The We Servie Business Proess Exeution Lnguge (BPEL) lks ny stnr grphil nottion. Vrious efforts hve een unertken to visulize BPEL using the Business Proess Moelling Nottion (BPMN). Although this is strightforwr for the mjority of onepts, it is triky for the full BPEL stnr, prtly ue to the insuffiiently speifie BPMN exeution semntis. The upoming BPMN 2.0 revision will provie this ler semntis. In this pper, we show how the e pth elimintion (DPE) pilities of BPEL n e expresse with this new semntis n isuss the limittions. We provie generi forml efinition of DPE n isuss resulting ontrol flow requirements inepenent of speifi proess esription lnguges. Keywors-BPEL, BPMN, e pth elimintion, moel trnsformtion, roun-tripping, proess moel lignment I. INTRODUCTION The Business Proess Moeling Nottion (BPMN) [1] s stnrise y the OMG hs emerge s the e-fto stnr for usiness proess moelling. Its evelopment ws t lest prtly riven y the lk of ny stnr grphil nottion for the We Servie Business Proess Exeution Lnguge (BPEL) [2] whih is the leing stnr in the fiel of We Servie orhestrtions. Between the poles of high-level usiness lignment n low-level proess entment, lot of reserh hs een onute on trnsformtions etween oth lnguges [3] [7]. A iiretionl lignment, however, suffers from oneptul mismthes [8]. In n erlier work, we revele BPEL s e pth elimintion (DPE) pilities s mjor issue for BPEL-to-BPMN trnsformtions, in prtiulr [9]. In generl, DPE refers to ontrol flow onept tht supports expliit skipping of tivities. Skipping n tivity n then le to the skipping of susequent tivities, to eliminte the e pth. By using onitions (onitionl DPE), susequent tivities n e exeute even though preeing tivities were skippe. This pper elortes on the relistion of DPE in BPMN. It relies on the semntis of the inlusive OR gtewy n the omplex gtewy. For oth onstruts, the urrent BPMN stnr [1] oes not provie n unmiguous efinition [9], [10]. The upoming revision 2.0 of BPMN [11] resses the exeution semntis of ll onstruts. In this pper, we evlute BPMN s DPE pilities se on the ltest puli rft of BPMN 2.0 [11] n the new semntis to e expete. We show how DPE n e relise in BPMN 2.0 n wht limittions remin. Bse thereon, we illustrte the pplition of our finings in the ontext of BPEL-to-BPMN trnsformtions. The reminer of this pper is struture s follows. Setion II illustrtes the onept of DPE y mens of n exmple proess, while we eite Setion III to forml efinition of DPE n isussion of its ontrol flow requirements. Afterwrs, Setion IV introues the relistion of DPE in BPM, isusses the mpping of DPE in BPEL to BPMN, n its limittions. We review relte work in Setion V n onlue in Setion VI. II. EXAMPLE WITH DEAD PATH ELIMINATION In orer to illustrte the essene of e pth elimintion, Figure 1 epits n exemplry BPEL proess. This orer-toshipping senrio is visulise in nottion similr to the one use in the BPEL speifition. The proess is triggere y the reeption of purhse orer. Afterwrs, flow tivity is tivte whih, in turn, strts two single tivities n two sequenes of tivities in prllel. Four of the tivities hve outgoing ontrol links (links for short) nme with smll letters, while trnsition onitions re elre t the soure of the links. Further on, join onition is speifie for tivity Sheule Proution. Semntis for this exmple re s follows: After n tivity with n outgoing link (e.g. Customer Sttus) ens, the trnsition onition (e.g. Mster Agreement?) is evlute n epening on the result, the ontrol link is set to either true or flse. These Boolen link vlues re onsiere in join onitions. Thus, tivity Sheule Proution is exeute only, if the orere items re not on stok t the shipping hus or if there exists mster greement with the ustomer. Skipping of tivity Sheule Proution will set its outgoing link to flse, whih invrily les to skipping of tivity Sheule Trnsport to Shipping Hu. This ehviour is referre to s e pth elimintion. III. DPE IN BUSINESS PROCESSES De pth elimintion (DPE) hs een wiely isusse in the ontext of exeutle workflows [12] [14]. However, we re not wre of onise moel tht ptures the essene of DPE formlly. Therefore, this setion efines

2 Sequene (suppressjoinfilure= yes ) Flow Customer Sttus Mster Agreement? Figure 1. Shipping Hu 1 Stok Empty? Sheule Trnsport To Shipping Hu Reeive Purhse Orer Sequene Store Orer ( Λ ) V Sheule Proution Sheule Shipping From Hu BPEL exmple senrio with DPE Sequene Shipping Hu 2 Stok Empty? Upte Sttistis DPE in the first prt. Bse thereon, we isuss the resulting requirements for token-flow se lnguges n nlyse the well-known workflow ptterns for overge of these requirements. Afterwrs, we present short survey on the pilities of ommon proess lnguges to ope with DPE. A. Definition of De Pth Elimintion First n foremost, we speify the notion of n yli proess moel in orer to provie onise efinition of the very ore of DPE. The efinition of n yli proess moel hs een inspire y the notion of synhronizing workflow moels s presente in [15]. Definition 1 (Proess Moel (PM)): A proess moel is tuple P = (N, ), where N is set of proess noes n N N is flow reltion onneting proess noes. P is lle yli, if the flow reltion is yli. As n revition we will use n s the set of ll rs iretly preeing n, i.e. n := {(x, y) y = n}. n is efine oringly for sueeing rs. Bse thereon, we efine proess moels, for whih the exeution of eh noe is pture y reltion tht onsiers the stte of its preeing rs. The set of sttes is given y S = {, exeute, skippe}. Definition 2 (PM with Expliit Enling): A proess moel with expliit enling is tuple P e = (N,, signl, ex) where (N, ) is n yli proess moel n for every noe n, lel s S, signl(n, s) speifies sttes for rs sueeing n: signl(n, exeute) (n {, true, f lse}), signl(n, skippe) = (n {f lse}), signl(n, ) = (n { }), for every noe n, ex(n) speifies the omintions of sttes of its preeing rs for whih n will exeute, where ex(n) ( n {true, flse}), suh tht e ex(n), n [ s S [ (, x) e ]]. From here on, we use the term proess moel to refer to n yli proess moel with expliit enling. The efinition of ex implies tht ritrry omintions of r sttes n e efine to trigger exeution. Figure 2 shows n exmple where noe n hs two preeessors n, i.e. n = {(, n), (, n)}. As speifie in the signl signl(,exeute) = {((,n),flse)} signl(,skippe) = {((,n),flse)} n ex(n) = {{((,n),flse),((,n),true)}, {((,n),flse),((,n),flse)}} Figure 2. enling Smple for onitionl reltion, r (, n) is set to flse in ll ses, i.e. might hve een exeute or skippe. It is worth to mention tht our efinition llows rs only to e set to true, if their soure noe hs een exeute. Further on, n will exeute if r (, n) is in stte flse n (, n) in stte true or flse. Further, we efine ex 1 (n) s the reltion ontining ll tuples of r / stte omintions, not leing to n exeution of n, i.e. ex 1 (n) = ( n {true, flse}) \ ex(n). Next, we present restritions on ex y introuing proess moels with plin enling s speil ses. While proess moels with onitionl enling n use ex to efine ritrry enling onitions, for proess moels with plin enling the ex reltion ontins ll ses in whih t lest one inoming r is true. Definition 3 (PM with Plin Enling): Let P e = (N,, signl, ex) e proess moel. Then, P e is proess moel with plin enling, if for ll noes n N it hols ex(n) {( n {flse})} =. The exmple from Figure 2 oes not show plin enling. Here, ex(n) woul look s follows in orer to omply with plin enling: ex(n) = {{((, n), true), ((, n), true)}, {((, n), true), ((, n), flse)}, {((, n), flse), ((, n), true)}}. Further on, we hrterise proess instnes y the notion of their stte, while negleting mens to istinguish ifferent instnes. Definition 4 (Stte of Proess Instne): Let P e = (N,, signl, ex) e proess moel. Then tuple I = (N,, signl, ex, st) is proess instne of P e in ertin stte, where st : N {, exeute, skippe} is funtion ssigning sttus lels to noes. The stte of proess instne is given y the funtion st. For ovious resons, ll noes re neither exeute nor skippe in the initil stte, i.e. n N : st(n) =. In orer to pture the ehviour of proess instne, we speify its semntis using stte trnsition system. The trnsition reltion is efine y set of trnsition rules, onsisting of ontext, soure stte n trget stte. The ontext is set of gur onitions, whih hve to hol in orer for the rule to pply. Semntis for the proess instne re given y the following three trnsition rules ( ontext is note ove the line, while the trnsition from the

3 soure stte to the trget stte is note elow the line). As shorthn nottion, we use n := {x N x n} for noes preeing n. Init st(n) = n = st (st \ (n, )) (n, exeute) 1 t1 ( I ) ( II ) ( III ) s 2 t2 s1 t s2 s1λ s2 s1 t s2 s1vs2 ( IV ) s t s Exe st(n) = p n signl(p, st(p)) ( n S) ex(n) st (st \ (n, )) (n, exeute) Figure 3. Control flow requirements Skip st(n) = p n signl(p, st(p)) ( n S) ex 1 (n) st (st \ (n, )) (n, skippe) Rule Init strts proessing of the proess instne, s it represents the exeution of noe without preeessors, rule Exe mrks the exeution of noe n, n rule Skip relises skipping. The tul hoie etween these two rules is se on ex(n). We test whether the omintion of the sttes of preeing rs is ontine in ex(n) or ex 1 (n). These sttes, in turn, re etermine y evluting the signl funtion for ll preeing noes. Plese note, tht in oth rules it is impliitly ensure tht ll preeessors of the respetive noe hve een either skippe or exeute. After we introue our forml fountion for proess moels n proess instnes, we re le to pture the hrteristis of DPE. Definition 5 (De Pth Elimintion): Let I = (N,,ex,st) e proess instne in ertin stte. Then the term e pth elimintion refers to stte trnsition esrie y trnsition rule Skip uring proessing of I. B. DPE Requirements on Token Flow Aoring to the forml moel presente in the previous setion, enling of noe is se on the stte of ll preeing rs. These r sttes, in turn, epen on the stte of their soure noes (however, they might not e equl, e.g., n tivity might e skippe, ut the outgoing links re set to true). In ontrst to tht, ommon proess esription lnguges tivte noes se on token pssing. Thus, efore we re le to summrise the requirements of DPE, we hve to ress how r sttes re propgte using token flow. There re three possile relistions. Type Tokens If the proess esription lnguge supports t lest two istinguishle types of tokens (true n flse tokens), the stte of n r is inite y sening orresponing token. One Ar n Non-Lol Semntis A token is sent on n r to inite the stte true. Non-lol semntis is pplie to istinguish the sttes flse n of the respetive r. Deite Ars There re two rs representing the sttes true n flse, respetively. An untype token is sent exlusively on one of them. Bse thereon, we summrise the requirements of DPE on token flow se lnguges s epite in Figure 3. First, we nee to e le to tivte rnh uner speifie onitions, s noe tivtion might not imply tivtion of the sueeing rnhes. Thus, mens to sen tokens se on onitions re essentil (I). In orer to relise DPE, we lso hve to merge ontrol flow se on join onition (II). This onition referenes the sttes of preeing rs. Thus, it orrespons to the reltion ex in Definition 2. The onrete relistion of this flow pttern epens on the wy the r sttes re inite using token flow. Requirement (II) n e further lssifie. In orer to relise plin DPE, the join onition must require tht one of the preeing rs hs een tivte (III). Another importnt speilistion of requirement (II) is join onition tht n express tht preeing r ws not tivte (IV). C. Going Beyon Workflow Ptterns It is worth to notie tht the forementione requirements re not overe y the well-known ontrol-flow ptterns [16] of the workflow ptterns frmework 1 to the full extent. While requirement (I) is pture y the Multi-Choie pttern, support for the requirements epens on how the r stte (true or flse) is propgte. In se of type tokens, requirements (III) n (IV) re pture y the Lol Synhronizing Merge pttern, wheres the generlistion of oth ptterns, nmely requirement (II), nnot e tre k to ny pttern. There is no mens to speify n ritrry join onition over the type of reeive tokens. If one r n non-lol semntis re use to moel the stte of n r, requirement (III) is overe y the Generl Synhronizing Merge pttern. However, requirement (IV) is not pture. The ontrol flow pttern requires n tivtion of t lest one of the inoming rs, whih is not the se for requirement (IV). Agin, requirement (II) is lso not support s join onitions se on the stte of inoming rs nnot e expresse. In se eite rs re use to inite r sttes, requirement (IV) is overe y the Simple Merge pttern, wheres requirements (II) n (III) re not pture iretly. A workroun woul e to enoe join onition using Synhronistion n Simple Merge ptterns. Due to the implie 1

4 Tle I SUPPORT FOR DPE Lnguge Support for plin DPE Support for on. DPE WS-BPEL 2.0 ontrol links ontrol links, join onitions UML AD EPC OR-split, OR-join 2, onitionl events YAWL OR-split, OR-join verosity, it seems questionle, whether this workroun is fesile for omplex senrios. All possile omintions of tivity sttes tht stisfy the join onition woul hve to e moelle expliitly. We oserve tht the limite overge of the requirements for DPE minly results from the neglet of r ientities in ll ontrol flow ptterns. In ontrst to iverging ptterns (e.g. Multi-Choie), onverging ptterns lwys ssume inistinguishle rs. This prelues ny possiility to speify merging ehviour se on onition over the type of inoming tokens or the stte of inoming rs. Even if two eite rs re use to propgte noe stte, these two rs nnot e orrelte in the set of inoming rs. D. DPE in Proess Desription Lnguges In the following, we present short survey on the pilities of ommon proess esription lnguges to relise DPE senrios. An overview is given in Tle I. As isusse for the exmple in Setion II, BPEL [2] supports DPE through ontrol links, trnsition onitions, n join onitions in flow onstrut. BPEL prohiits yli link epenenies n ontrol links must not enter or leve repetle onstruts. The BPEL semntis might le to ifferent ehviour of proess with n without DPE. Tht results from the potentil usge of negtion opertor in join onitions n the requirement to wit for synhronistion of ll rnhes efore the join onition is evlute. This phenomenon, referre to s sie effet, hs een stuie y vn Breugel n Koshkin in [17]. They lso propose ifferent DPE semntis for BPEL to voi sie effets, s they ssume these effets to e unintene in ny se. With our efinition of DPE in Setion III-A, we o not follow this opinion n omply with the existing BPEL semntis tht hs expliitly een ffirme y the OASIS WS-BPEL Tehnil Committee. The ommittee rejete proposl to restrit join onitions in orer to voi sie effets (f. issue 14 in the WS-BPEL Issues List 3 ). UML [18] introues Ativity Digrms (AD) in orer to esrie usiness proesses. Conitionl ivergene of rnhes n e expresse y fork noes with gur 2 The OR-join hs unerspeifie exeution semntis in EPCs. 3 puli/ownlo.php/11285/ wspel issues34.html#issue14 onitions. In orer to join onurrent rnhes, UML AD introue join noes. A plin join noe synhronises, if ll inoming rs hve een tivte. Further on, join speifition llows for further speifition of the merging ehviour. Aoring to [18], join speifition is onjuntion { joinspe = n } A B C Figure 4. AD D JoinSpe in UML of ientifiers of suset of inoming rs s illustrte in Figure 4. Thus, there re no mens to synhronise multiple rnhes, of whih only suset hs een tivte efore (i.e. there is no OR-join in UML AD). Even in se the isjuntion opertor woul e llowe in the join speifition, this issue woul not e resolve s isusse in [19]. Work on formlistion of semntis of UML AD [20], [21] typilly neglets the join speifition. Owing to the restrite expressiveness of the join speifition, UML AD support neither plin DPE nor onitionl DPE. While we n moel onitionl ivergene of rnhes in EPCs [22] iretly, lot of reserh hs een onute on the orresponing onvergene of rnhes through n OR-join [23], [24]. Groune on n OR-join formlistion, Menling shows the relistion of plin DPE in [25] when mpping BPEL to EPCs. However, onitionl DPE is not supporte ue to the sene of onstrut tht llows for merging of multiple rnhes se on onition. This lso prohiits ny relistion of DPE with eite rs to istinguish the true n flse stte. Aiming t inrese support for workflow pttern n well-efine semntis for the OR-join onstrut, vn er Alst n ter Hofstee introue YAWL in [26]. YAWL semntis re groune on untype token flow. Plin DPE is supporte vi OR-splits n OR-joins. As flow reltion entities re inistinguishle in YAWL, we nnot speify onitionl onvergene ehviour. Thus, onitionl DPE is not supporte. IV. DEAD PATH ELIMINATION IN BPMN This setion shows how e pth elimintion n e relise in BPMN. We first show the relistion of plin DPE n then isuss the hllenges ssoite with onitionl DPE. Afterwrs, DPE is reviewe isusse in the ontext of BPEL-BPMN-trnsformtions. In generl, semntis for BPMN re se on untype token flow, whih exlues the possiility to pply true n flse tokens in orer to propgte stte of n tivity (f. Setion III-B). As mentione efore, two onstruts tht re importnt for DPE hve unerspeifie semntis in the urrent BPMN stnr [9], [10]. Therefore, we se our isussion on the semntis propose in the ourse of the BPMN 2.0 stnristion [11].

5 signl(,exeute) = {((,),true),((,),flse)} ex() = {{((,),true),((,),flse),((e,),flse)}, {((,),flse),((,),true),((e,),flse)},, {((,),true),((,),true),((e,),flse)},...} ex -1 () = {{((,),flse),((,),flse),((e,),flse)}} Figure 5. A. Relistion of Plin DPE e 4 Relistion of plin DPE in BPMN Aoring to our forml moel efine in Setion III-A, plin e pth elimintion requires ertin tivity to e exeute, if one of the preeing rs hs een set to true. Therefore, the enling onition n e seen s n inlusive isjuntion over the sttes of preeing rs. Consequently, we n se our relistion on one r n nonlol semntis (f. Setion III-B) in orer to istinguish the sttes (true n flse) of n r. We illustrte the relistion y mens of the exemplry proess moel tht is epite on the left sie of Figure 5. It hs two noes without preeessors, n e, tht re exeute initilly. Afterwrs, the stte for rs strting t these noes re set se on the reltion signl whih is illustrte for noe. Further on, we see tht the ex reltion requires t lest one of the preeing rs of noe to e in stte true whih orrespons to plin DPE onfigurtion. The relistion of this senrio in BPMN is groune on onitionl flow n the merging inlusive OR-gtewy s illustrte on the right sie of Figure 5. The joint exeution of ll noes without preeessors is relise using prllel split gtewy in front of the respetive BPMN tivities. In generl, the stte true of n r in our forml moel is represente y sening token on the respetive sequene flow in BPMN. In our forml moel, stte of n r is erive vi the reltion signl. This onition, in turn, is reflete y the onitionl flow in the orresponing BPMN moel. The reltion signl oes only onsier the noe sttes, however, the orresponing onitions (1, 2, 3, 4, n 5) in the BPMN moel might lso e se on proess t, s the istint reltion etween the noe sttes n the r sttes is not require to oserve DPE. Further on, the sttes flse n of n r in our forml moel hve to e istinguishe in the respetive BPMN moel s well. This is hieve y the non-lol semntis of the OR-join. Tht is, the join wits for ll tokens nywhere upstrem of this sequene flow, i.e. there is no pth from token to this sequene flow unless the pth visits omintor 5 e or postomintor [..] A noe omintes sequene flow if eh pth from soure of the grph to the sequene flow visits tht noe. [11]. Due to the yli nture of our DPE moel, postomintors will never impt on the semntis of the OR-join n t most one token will e sen on eh r. Therefore, the r stte flse of our forml moel n e represente y the sene of sent token whih is etete y the OR-join semntis. Note tht stlling of the proess is possile even in plin DPE onfigurtion. Regring the exmple in Figure 5, we oul efine signl(, exeute) = {((, ), flse), ((, ), flse)}. Thus, the rs sueeing noe re lwys set to f lse. Tht woul result in skipping of oth noes n. If lso signl(e, exeute) = {((e, ), flse)}, noe will e skippe. In plin DPE onfigurtion ll potentil noes fter will e skippe either, s the reltion signl n set n r stte to true solely if the soure noe hs een exeute (f. Definition 2). This omplies with our BPMN moel s no tokens re sent fter tivities n e hve een exeute. Consequently, nother tivity might never e exeute fterwrs. B. Relistion of Conitionl DPE In ontrst to plin DPE, onitionl DPE llows for the speifition of n ritrry omintion sttes of preeing rs in orer to exeute ertin tivity. Therefore, the ORjoin nnot e pplie s in the se of plin DPE. Nomen est omen, however, the omplex gtewy is intene to moel omplex synhroniztion ehviour [11]. In generl, firing ehviour of the omplex gtewy is speifie using n tivtion expression whih is evlute with the reeption of every token. It might referene seprte token ounters for eh of the iretly preeing flow rs (ut not for flow rs elsewhere in the moel). One the tivtion expression evlutes to true, token is rete on the norml output flow. Afterwrs, the gtewy wits for token on eh of those inoming gtes tht it hs not yet reeive token in the first phse unless suh token oes not ome (f. inlusive join ehviour) [11]. Thus, the non-lol semntis known from the OR-join is reuse. Finlly, the gtewy resets y reting token on the optionl reset output flow. Conitionl DPE without negtion. First, we onsier onitionl DPE without negtion. Tht is, join onition requires ertin flow r to e either in stte true or oth sttes (true,f lse) re llowe in the join onition (see r (, ) in Figure 6). Tht is, whenever n exeution onfigurtion (i.e. set in ex(n)) speifies stte flse for n r, ex(n) hs to ontin nother exeution onfigurtion, in whih this r is require to e true, wheres the sttes for ll other rs remin unhnge. Formlly, for ll noes n it hols e ex(n), t [(t, flse) e e 2 ex(n)[e 2 \ e = {(t, true)}]]. In this se, semntis of the omplex gtewy llow for the relistion of onitionl DPE s illustrte in Figure 6. This

6 ex() = {{((,),true),((,),true),((,),flse)}, {((,),true),((,),true),((,),true)}} ( Λ ) Figure 6. Figure 7. Relistion of onitionl DPE without negtion in BPMN ex() = {{((,),flse),((,),true)} ( Λ ) Conitionl DPE with negtion nnot e relise in BPMN relistion resemles the one introue for plin DPE exept for the mpping of the join onition. In the proess moel on the left sie noe is exeute solely if the preeing rs from noe n re set to true. This onition hs to e enoe in the tivtion expression of omplex gtewy. It requires the token ounters of two gtes to e igger thn one, i.e. t 1 t 1. With the rrivl of every token (initing the stte true for the respetive r) this onition is evlute. Plese note tht for ll tivities potentilly sueeing tivity the following property hols ue to our ssumptions. For suh n tivity, the eision of exeution is either se on the stte true propgte on the pth oming from, or this pth oes not impt on this eision. Conitionl DPE with negtion. In se join onition ontins negtion, onitionl DPE nnot e relise in BPMN iretly. Tht is ue to the missing possiility to test for token sene on one of the inoming rs of the omplex gtewy. Even if the tivtion expression requires ertin token ounter to e zero, it might e the se tht token rrives t lter stge. Consier, for instne, Figure 7. Setting the tivtion expression to t = 0 t 1 woul le to unintene firing of the omplex gtewy in se exeution of tivity finishes efore exeution of finishe (ssuming tht oth tivities sen token on their outgoing onitionl flow). Therefore, this kin of onitionl DPE n only e relise if ifferent pproh is hosen in orer to istinguish the r sttes of our forml moel. As mentione in Setion III-B, two eite rs might e pplie in orer to represent the true n flse sttes of suh n r. ( Λ ) ( V ) Figure 8. Relistion of onitionl DPE with negtion is not fesile However, this pproh oes not seem fesile ue to the enormous overhe whih is illustrte in Figure 8 for the forementione join onition. C. BPEL Control Links in BPMN In ontrst to BPMN, BPEL supports the full rnge of DPE vrints. BPEL senrios showing plin DPE or onitionl DPE without negtion n e mppe to BPMN. For these senrios the mpping iretly follows from the relistion s esrie ove. However, lok-struture ontrol flow elements tht re prt of proess with DPE hve to e onsiere oringly. This is shown in Figure 9 whih illustrtes the BPEL proess from Setion II (whih shows onitionl DPE without negtion) in BPMN. We see tht the lok-struture BPEL tivities, e.g. the BPEL sequenes, result in itionl sequene flows. These flows hve to e synhronise using OR-join onstruts in orer to preserve the exeution semntis of the lok-struture tivities. Consier, for instne, tivity Sheule Shipping from Hu. It hs to e exeute fter tivity Store Orer, wheres tivity Sheule Proution might e exeute in etween, epening on the evlution of its join onition. To ope with this potentil exeution, the inlusive OR gtewy sueeing Sheule Proution is tivte one the first tivity Store Orer finishe exeution. Due to the non-lol semntis, it is ensure tht Sheule Shipping from Hu will only e exeute if Sheule Proution hs finishe or nnot e exeute t ll. Plese note tht there is still slight ifferene in exeution semntis etween the BPEL n the BPMN proess. As omplex gtewy representing join onition fires immeitely fter the onition is fulfille, susequent tivity (e.g. Sheule Proution) might run onurrently to tivities preeing the omplex gtewy (e.g. Hu 1). This potentil onurreny nnot our in the BPEL proess euse BPEL join onitions re evlute only fter ll links re set. V. RELATED WORK Besies the numerous pulitions on BPEL-BPMNtrnsformtions [3] [9], two fiels of reserh re further relte to our work. On the one hn, there re multiple pttern-se ssessments of BPMN n BPEL reveling ifferenes in their expressiveness with respet to ontrol

7 f f Λ Sheule Trnsport To Shipping Hu Customer Sttus Hu 1 Store Orer f f Λ (( Λ ) V ) Sheule Proution Hu 2 Upte Sttistis onitionl DPE without negtion n e relise iretly (lthough the ltter implies slight evition in semntis), wheres onitionl DPE with negtion nnot e expresse in fesile mnner. Tht, in turn, implies limittions for ny BPEL-BPMN-trnsformtion. We solely skethe suh trnsformtion for DPE, so tht onrete trnsformtion lgorithm is still to e presente. Moreover, the rther omplex relistion of onitionl DPE without negtion in BPMN rises questions onerning negtive impt on the unerstnility of the moel. Although semntis might e preise, the intrinsi omplexity of suh senrios might e seen s reson to voi onitionl DPE in BPMN moels. REFERENCES Sheule Shipping From Hu [1] OMG, Business Proess Moeling Nottion (BPMN) 1.2, Jnury [2] We Servies Business Proess Exeution Lnguge Version 2.0, OASIS, Jnury Figure 9. The exmple senrio in BPMN flow, t flow, n proess instntition mehnisms [27] [30]. Aleit se on oler versions of oth stnrs, these ssessments revel serious evitions etween oth lnguges. On the other hn, work on formlistions of oth lnguges is relte. Numerous pprohes hve een presente in orer to formlise BPEL semntis, refer to vn Breugel n Koshkin [31] for n overview. Most of these pprohes pture lso BPEL s DPE pilities. For BPMN, existing formlistions [32] [35] re se on former versions of BPMN. They either omit the inlusive OR n omplex gtewy or mke ssumptions tht o no longer hol true ue to BPMN 2.0. VI. CONCLUSION In the first prt, we elorte on the onept of e pth elimintion (DPE) in generl. We introue forml moel pturing the essene of DPE, erive requirements for token flow se lnguges, n gve n overview of support for DPE in ommon proess esription lnguges. Bse thereon, our seon ontriution is esription of how DPE n e relise in BPMN ssuming semntis propose for BPMN 2.0. As DPE in BPMN is motivte y n lignment with BPEL, we lso isusse to whih extent BPMN 2.0 n e use to represent BPEL regring DPE senrios. A mjor result of our work is the preise esription of ifferent kins of DPE long with isussion, whih of these DPE vrints n e relise in BPMN. Plin DPE n [3] S. White, Using BPMN to Moel BPEL Proess, BPTrens, vol. 3, no. 3, pp. 1 18, [4] C. Ouyng, M. Dums, A. H. M. ter Hofstee, n W. M. P. vn er Alst, From BPMN Proess Moels to BPEL We Servies, in ICWS. IEEE Computer Soiety, 2006, pp [5] O. Kopp, D. Mrtin, D. Wutke, n F. Leymnn, On the Choie Between Grph-Bse n Blok-Struture Business Proess Moeling Lnguges, in MoIS, ser. LNI, vol GI, 2008, pp [6] J. Menling, K. Lssen, n U. Zun, On the Trnsformtion of Control Flow etween Blok-Oriente n Grph-Oriente Proess Moeling Lnguges, IJBPIM, vol. 3, pp , Otoer [7] D. Shumm, D. Krstoynov, F. Leymnn, n J. Nitzshe, On Visulizing n Moelling BPEL with BPMN, in Proeeings of the 4th Interntionl Workshop on Workflow Mngement (ICWM2009). IEEE Computer Soiety, My 2009, Workshop-Beitrg. [8] J. Reker n J. Menling:, On the Trnsltion etween BPMN n BPEL: Coneptul Mismth etween Proess Moeling Lnguges, in CAiSE Workshop Proeeings - EMMSAD, June 2006, pp [9] M. Weilih, G. Deker, A. Großkopf, n M. Weske, BPEL to BPMN: The Myth of Stright-Forwr Mpping, in OTM Conferenes (1), ser. LNCS, vol Springer, 2008, pp [10] M. Dums, A. Großkopf, T. Hettel, n M. T. Wynn, Semntis of Stnr Proess Moels with OR-Joins, in OTM Conferenes (1), ser. LNCS, vol Springer, 2007, pp

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