Communicating MMS Events in a Distributed Manufacturing System Using CORBA

Copy igh © IF AC Dis ibu ed Compu e Con ol Sys ems, Coma, I aly, 1998 COMMUNICATING MMS EVENTS IN A DISTRIBUTED MANUFACTURING SYSTEM USING CORBA T. A iza' F .R. Rubio· • Depa amen o de Ingenie ia de Sis emas y A u oma ica, Uni e sidad de Se illa, Escuela Supe io de Ingenie os, Gamino de Los Descub imien os sin . E-41092 Se illa, Spain. Phone: +34 95 446 7364· Fax: +34 95448 73 85 . E-mail: [email p o ec ed] Abs ac : Nowadays, dis ibu ed compu ing sys ems a e widely used due o he g ea ad ances ha ha e been achie ed in compu e ne wo ks in he pas ew yea s, and pa ly due o hei low cos . De eloping so wa e o hese sys ems u ns ou o be complica ed, mainly due o he he e ogenei y o he dis ibu ed sys em componen s and he unde g ound communica ion laye s. MMS is a sui able language o ca y ou he communica ion be ween de ices in a he e ogeneous manu ac u ing sys em because i p o ides uni o mi y in he access o hem . This wo k p oposes he use o he ORB speci ied in CORBA om he OMG o communica e MMS e en s. Copy igh © 1998 IFAC Keywo ds: Dis ibu ed models, Objec -O ien ed p og amming, Communica ion p o ocols, E en s, Manu ac u ing Sys ems. 1. INTRODUCTION Dis ibu ed sys ems ha e ob ained g ea impo - ance in he pas ew yea s. They ha e been in- oduced in o a g ea di e si y o en i onmen s and explici ly in manu ac u ing sys ems. So ha , whe e he e we e isola ed componen s, he e a e now in eg a ed componen s in he dis ibu ed compu ing sys em, whe e he communica ion and coope a ion be ween hem is allowed. This ad an age is dec eased due o he he e o- genei y o he de ices ha can be ound in he manu ac u ing en i onmen s. Because o his, he necessi y o using a common p o ocol in o de o communica e hese in e connec ed elemen s a ises. In addi ion o his, using se ices p o ided by he p o ocol mus be easy om he poin o iew o he use applica ion. MMS is a communica ion p o ocol widely used in manu ac u ing dis ibu ed sys ems. I is an applica ion laye p o ocol ha homogenises he use o he de ices ha compound he sys em . MMS makes use o he objec o ien ed app oach o speci y he se ices ha a use can in oke o communica e wi h hese de ices. 149 On he o he hand , dis ibu ed objec me hod- ologies, whe e CORBA is amed, p o ide all he objec o ien ed me hodology ad an ages in dis- ibu ed sys ems. CORBA can make he MMS se ice use applica ion o eques he se ice easie , as i allows o s uc u e he sys em in objec s and a he same ime o ha e hese objec s dis ibu ed along he se e al componen s o he sys em, making he dis ibu ion anspa en o he use . Taking his in o accoun , esea ch has been un- de aken, bu hey do no deal wi h he e en communica ion, an impo an aspec o he MMS p o ocol ha allows o send e en no i ica ions o and om manu ac u ing de ices. The obje i e o his wo k is o p opose CORBA as he me hodology used o communica e MMS e en s in manu ac u ing en i onmen s. In he ol- lowing sec ions, he aim o his pape will be p e- sen ed, as well as a summa y on he backg ound o i and he way o use CORBA in o de o communica e e en s. 2. AIM OF THE WORK Taking in o accoun he CORBA a chi ec u e, ha allows he spli o he sys em in objec s and communica ion o hese objec s in an easy way and aking in o accoun he VMD e en manage- men se ices, communica ing MMS e en s and ca ying ou se ice eques s by means o CORBA is p oposed. In his way, s uc u ing he dis ibu ed sys em in a se o objec s ha a e communica ed by means o se ice eques s is allowed. Bu his dis ibu ion is anspa en o he use because i is he Objec Bus ha unde akes he esponsibili y o ind he se e al objec s . And u he mo e, i is used o communica e MMS e en s o he se e al VMD's. This wo k p oposes o make a ailable he MMS se ices o he e en managemen by means o he CORBA Objec Bus. These se ices a e he se - ices speci ied in he MMS s anda d . The ansla- ion scheme o hese se ices o CORBA IDL a e going o be s udied. The se ices o he e en managemen in MMS a e di ided in wo g oups: The se ices ca ied ou by he MMS se e and he se ices ca ied ou by he MMS clien . This app oach is used o communica e clien s o he se e al Vi ual Manu ac u ing De ices by means o he ORB, using he MMS in e ace o e en s. 3. BACKGROUNDS In o de o unde s and he wo k ca ied ou , MMS, he e en model and CORBA a e going o be b ie ly in oduced. 3.1 MMS In dis ibu ed he e ogeneous sys ems, whe e each de ice has di e en ea u es, ca ies ou di e en asks and is p obably owned by a di e en manu- ac u e , he need o in e connec all de ices ha compound he sys em ises in o de o achie e he in eg a ion o each one in he whole sys em. I is possible o use wo di e en ocuses o allow he de ices o communica e: • Using he ools and he languages p o ided by he manu ac u e o each de ice. • Using a common language o all he de ices. This language mus be independen o he pa icula low le el ea u es. The disad an ages o his i s app oach a e e i- den : 150 • The specialised s a mus lea n he pa icu- la ea u es o each de ice. • The applica ion depends on he de ice. • I is di icul o debug and main ain applica- ions o hese sys ems. The second app oach does no ha e hese p ob- lems, because o his, he enginee in cha ge o de eloping applica ions ha un in he e ogeneous sys ems only has o lea n one language. Mo eo e , he applica ion will be independen o he de ice and he e o e easie o debug and main ain. Manu ac u ing Message Speci ica ion (MMS) can be used in his second app oach. MMS is a com- munica ion language o aid he in e connec ion o de ices in a he e ogeneous en i onmen . I is a p o ocol ha alls in he applica ion le el s an- da dised by ISO (In e na ional S anda d O gani- sa ion). Al hough MMS is no a comple e Objec -O ien ed language, as i does no suppo all he ea u es o he Objec -O ien ed p og amming, i spli s he sys em in objec and p esen s a well de ined in e - ace o each one. The mos impo an objec in he sys em is he Vi ual Manu ac u ing De ice (VMD). The VMD hides he eal manu ac u ing de ice o he p og amme . The sys em is s uc- u ed in a se o VMD. MMS is also based on he clien /se e model. The VMD ac s as a se e , and so ca ies ou a se o se ices ha a e desc ibed in he MMS p o ocol. The clien s a e he eques e s o he se ices p o ided by he VMD. A pa icula implemen a ion o he MMS se e mus p o ide he mapping be ween he VMD model, which is an abs ac ion, and he unc ion- ali y o he eal manu ac u ing de ice. ( Real De ice ( Real De ice Fig. 1. Sys em based on MMS. The scheme o a sys em based on he communica- ion p o ocol MMS is showed in igu e 1. Each MMS se e manages a se o objec s asso- cia ed o he VMD. Some o he mos impo an a e he ollowing: • The Damain Objec : I ep esen s a subse o he capabili ies o he VMD which is used o a speci ic pu pose. • The P og am In oca ion Objec : I is a dynamic elemen which mos closely co e- sponds o an execu ion h ead in a mul i- asking en i onmen . • The a iable Objec : I is used o model eal a iables o he VMD. O he impo an objec s ha a e managed by he VMD a e e en s. These objec s a e explained in he nex sec ion. In o de o handle hese objec s, he VMD p o- ides a se o se ices o hem. A e ision o MMS can be ound in (Pimen el, 1990; CCE-CNMA, 1995) and a comple e desc ip- ion o all hese se ices and he p o ocol speci i- ca ion in (ISO/IEC . 9506-1, 1990; ISO/IEC . 9506- 2, 1990). 3.2 MMS EVENTS The e en managemen se ices p o ide acili ies which allow a clien MMS-use o de ine and manage e en objec s a a VMD and o ob ain no i ica ions o e en occu ences. The e en managemen model ex ends he VMD wi h h ee addi ional objec s and se ices ha wo k in hese objec s. Each one o hese objec s models a speci ic aspec o he s a e in o ma ion associa ed o he MMS e en managemen . They a e b ie ly commen ed on in he ollowing: • The E en Condi ion Objec : The e en managemen model de ines wo classes o E en Condi ion objec , Ne wo k- igge ed e en condi ion objec and Moni- o ed E en Condi ion objec . The i s one models an e en which occu s due o he explici eques o a clien using he T ig- ge E en se ice. Al hough i also models e en s occu ing in e nall y, as a esul o au onomous VMD ac ion. The second one is a i ual ep esen a ion o an aspec o he ac i i y o he VMD which ep esen s a signi ican occu ence in he p ocessing o he VMD. Ei he class o E en Condi ion objec includes he po en ial o VMD ini ia ion o E en No i ica ion se ice execu ions. • The E en Ac ion Objec : I models he po ion o he s a e in o ma- ion which is conce ned wi h he execu ion o MMS se ices due o he occu ence o an e en . An E en Ac ion is a con i med MMS se ice which will be execu ed when a speci ic ansi ion o a s a e a ibu e o he E en Condi ion objec is de ec ed. • The E en En ollmen Objec : I is used op ionally in o de o bind an E en Condi ion objec o an E en Ac ion 151 objec and o bind he no i ica ions ha a e esul s o an e en ansi ion o a clien . I ep esen s he eques o a clien o be no i- ied o he occu ence o one o mo e speci ic ansi ions o he s a e a ibu e o he E en Condi ion objec , o o delay he execu ion o a con i med MMS se ice un il he occu - ence o one o mo e speci ic ansi ions o he s a e a ibu e o he E en Condi ion s a us. The se ices ha ha e been added o he VMD o manage e en s a e he ollowing: • In o de o de ine and dele e objec s: De i- neE en Condi ion , Dele eE en Condi ion, De ineE en- Ac ion , Dele eE en Ac ion, De ineE en En ollmen , Dele eE en En ollmen . • In o de o ob ain and modi y a ibu es : Ge E en Condi ionA ibu es , Al e E en Condi ion - Moni o ing , Ge E en Ac ionA ibu es, Ge E en En- ollmen A ibu es , Al e E en En ollmen . • In o de o ob ain ala m summa y : Ge Ala m- Summa y, Ge Ala mEn ollmen Summa y . • In o de o in o m abou he s a us ob- jec s: Repo E en Condi ionS a us , Repo E en- Ac ionS a us, Repo E en En ollmen S a us. • In o de o no i y e en s: T igge E en , E en - No i ica ion, Acknow ledgeE en N o i ica ion. 3.3 CORBA The Common Objec Reques B oke A chi ec- u e (CORBA) is a dis ibu ed objec a chi ec u e ha allows so wa e objec s o in e ac ac oss ne wo ks. CORBA was i s in oduced in 1991 by he Objec Managemen G oup (OMG). I is an in e na ional conso ium o o e 800 so wa e endo s, de elope s and end use s. The aim o his g oup is o speci y an open so wa e bus on which objec componen s w i en by di e en endo s can in e ope a e ega dless o he implemen a ion language, loca ion o hos pla o m. The objec bus p o ides an Objec Reques B o- ke (ORB) ha le s clien s in oke me hods on emo e objec s ei he s a ically o dinamically. As a esul o hei wo k, OMG app o ed a se o speci ica ions -called CORBA 2. 0- in la e 1994. The Objec Managemen A chi ec u e (OMA) speci ied by OMG, is shown in igu e 2 and con- sis s o he ollowing elemen s: • Objec Reques B oke (ORB) : I p o- ides he mechanisms by which objec s ans- pa en ly make and ecei e eques s and e- sponses. In doing his, he ORB p o ides in e ope abili y be ween applica ions on di - e en machines in he e ogeneous dis ibu ed Non·s anda diud Ve ical Applica ion·speci ic In e aces App li ca ion Objec s 0 0 Domain· speci ic In e aces Domajn In e aces 0 0 Ho izon al Facili y In e aces Common Facili ies 0 0 OBJEC REQUEST BROKER (ORB) 0 0 Objec Se ices Gene al Se ice In e aces Fig. 2. The Objec Managemen A chi ec u e (OMA) speci ied by OMG. en i onmen s and seamlessly connec s mul i- ple objec sys ems. • Objec Se ices : They a e se ices ha complemen he unc ionali y o he ORB. These componen s s anda dize he li e-cycle managemen o objec s. • Common acili ies: Se ices o di ec use o applica ion objec s. I p o ide a se o gene ic applica ion unc ions ha can be con igu ed o he speci ic equi emen s o a pa icula con igu a ion. • Domain In e aces : They ep esen e i- cal a eas ha p o ide unc ionali y o di ec in e es o end-use s in pa icula applica ion domains. • Applica ion Objec s: They a e speci ic com- ponen s o end-use applica ions. An appli- ca ion is ypically buil om a la ge numbe o basic objec s -some speci ic o he appli- ca ion a hand, some domain speci ic, some om objec se ices and some buil om a se o common acili ies. The objec speci ica ion is ca ied ou using he In e ace De ini ion Language (IDL). I is a de- sc ip i e language used o de ine he in e ace h ough which a clien may access a se e . IDL p o ides ope a ing sys em and p og amming lan- guage independen in e aces o all he se ices and componen s ha eside on a CORBA bus. The s a ic me hod in oca ion used by he COR- BA's implemen a ion is shown in igu e 3 (CORBA also de ine a dynamic me hod in oca ion, bu i is no explained ). The ollowing componen s a e necessa y o ca y ou he in oca ion: • Cli en IDL s ub : Clien code used by an objec o encode in oca ions in a o m which can be handled by he ORB, and o decode eplies ecei ed ia he ORB. 152 Reques Objec Implemen a ions 00 Objec ~=::..J Adap e Objec Reques B oke (ORB) Fig. 3. Objec 's me hod's s a ic in oca ion. • Skele on: Se e code up-called by he ORB, capable o decoding eques s ansmi ed by he ORB, con e ing i in o an in oca ion o he implemen a ion objec , and encoding he esul s o be sen back o he clien ia he ORB. • Objec adap e : I de ines how an objec is ac i a ed . I can do his by c ea ing a new p ocess, c ea ing a new h ead wi hin an exis ing p ocess, o by eusing an exis ing h ead o p ocess. Mo e in o ma ion ega ding CORBA can be ound in (Objec Managemen G oup, 1995a; Objec Managemen G oup, 1995b). 4. SYSTEM DESCRIPTION In o de o s uc u e he sys em and o adap MMS o CORBA, he app oach p oposed in (G. Guyonne , 1997) has been ollowed. This CORBA app oach o ISO-MMS is known as COOL-MMS, because i has been hough o o he CHORUS-COOL sys em (CHORUS Sys- ems , 1996). The ea u es o he sys em can be summa ised in his way: • The MMSse e is a CORBA objec and i s in e ace co esponds o he MMS se ices p o ided by he VMD, i is de ined in a IDL speci ica ion. The e en se ices ha e been added so ha e en s can be communica ed. • The con i med MMS se ices a e decla ed as synch onous in oca ion me hods. • The eques o send unsolici ed in o ma ion is implemen ed by means o one-way in o- ca ion me hods. The MMSse e uses he T apSe e objec o he clien in o de o send his unsolici ed in o ma ion. The scheme o he sys em is shown in igu e 4. Al hough he associa ion managemen is no im- plemen ed due o he ac ha hey a e managed by he ORB , some conside a ions mus be made. Real De ice MM8-CUen Fig. 4. E en Managemen in CORBA. In some cases, in he objec s and se ices o he e en model, being able o indica e a speci ic associa ion is impo an . Fo example, he E en En ollmen objec has an a ibu e ha is a e e ence o he applica ion ha mus be ad ised wi h an E en No i ica ion se ice when he s a e o a a iable changes. Then, he MMS se e mus be capable o indica ing his o a clien . In he s anda d MMS, he applica ion e e ence is de ined as speci ied below: Applica ionRe e ence { SEQUENCE } ap- i le [0] AP- i le OPTIONAL, ap-in oca ion-id [1] AP-in oca ion-iden i ie OPTIONAL, ae-quali ie [2] AE-quali ie OPTIONAL, ae-in oca ion-id [3] AE-in oca ion-iden i ie OPTIONAL Bu his in o ma ion is only meaning ul in an OSI en i onmen . In CORBA, he ollowing applica- ion e e ence has been used: enum Applica ionRe e enceChoice { name, e e ence }; union Applica ionRe e ence swi ch (Applica ionRe e enceChoice) { 153 }; case name : Iden i ie ap-name; case e e ence: T apSe e ap- e e ence; This e e ence is he applica ion name o he e e - ence o a T apSe e objec . Ha ing he e e ence, he MMS se e can communica e wi h he clien di ec ly by means o he ORB. O he wise, ha ing he name, i can ob ain his e e ence asking o he Naming Se ices. 5. EVENT SERVICES IN CORBA In o de o ca y ou he ansla ion om ASN.1 o idl he speci ica ion In e -domain Managemen : Speci ica ion T ansla ion o The Open G oup (Open G oup, 1997) is ollowed. Nex , he example o he T igge E en se ice in idl and he way o ansla e he necessa y da a s uc u es om ASN.1 o idl is shown. The da a speci ied in he MMS p o ocol o ealize a eques and e u n he esponse o he T ig- ge E en se ices a e he ollowing. Iden i ie ::= VisibleS ing Objec Name : := CHOICE { md-speci ic } [0] IMPLICIT Iden i ie , domain-speci ic [1] IMPLICIT SEQUENCE { }, aa-speci ic domainId i emId [2] IMPLICIT Iden i ie Iden i ie , Iden i ie Unsigned8 :: = INTEGER P io i y ::= Unsigned8 T igge E en -Reques :: = SEQUENCE { } e en Condi ionName [0] Objec Name, p io i y [1] IMPLICIT P io i y OPTIONAL T igge E en -Response ::= NULL The co esponding s uc u e in idl ob ained by means o he ansla ion ollowing he speci ica- ion o he Open G oup a e he ollowing: ypede cha ASN1_Null; cons ASN1_Null ASN1_NullValue=' xOO'; ypede s ing ASN1_VisibleS ing; ypede ASN1_VisibleS ing Iden i ie ; ypede long ASN1_In ege ; ypede ASN1_In ege Unsigned8; ypede Unsigned8 P io i y; ypede ASN1_Null T igge E en _Response; enum Objec NameChoice { md_speci icChoice, domain_speci icChoice, aa_speci icChoice }; union Objec Name s i ch (Objec NameChoice) { case md_speci icChoice: }; Iden i ie md_speci ic; case domain_speci icChoice : s uc { Iden i ie domainId; Iden i ie i emId; } domain_speci ic ; case aa_speci icChoice: Iden i ie aa_speci ic; union P io i yTypeOp s i ch (boo lean) { case TRUE: P io i y alue; }; s uc T igge E en _Reques { Objec Name e en Condi ionName; P io i yTypeOp p io i y; }; The me hod in he MMSse e in e ace speci ied in idl is: T igge E en _Response T igge E en (T igge E en _Reques ) aises(Se iceE o ): Once he VMD in e ace o manage MMS e en s is de ined in idl, he MMSse e objec se ices o he e en managemen can be accessed h ough he ORB om any place in he manu ac u ing dis ibu ed sys em . 6. IMPLEMENTATION A p o o ype has been implemen ed. The unc ion o i is o accep eques s om he clien s and send uncon i med eques s o hem . I only deals wi h he communica ion o e en s. The e en managemen has no been implemen ed, bu some in o ma ion ega ding his can be ound in (Swiss Fede al Ins i ude o Technology, Lausanne, 1992). The ORB used is Ja aIDL. Ja aIDL is an Objec Reques B oke p o ided wi h he JDK 1.2. To- ge he wi h he idl oja a compile , i can be used o de ine, and access CORBA objec s om he Ja a p og amming language. Ja aIDL is compli- an wi h he CORBA 2.0 Speci ica ion and he IDL- o-Ja a Language Mapping. Ja aIDL also p o ides a ansien namese e o o ganize objec s in o a ee-di ec o y s uc- u e. The namese e is complian wi h he Naming Se ice Speci ica ion desc ibed in COR- BASe ices: Common Objec Se ices Speci ica- ion (Objec Managemen G oup, 1995b). 154 7. CONCLUSION The aim o de eloping his wo k is o ad ance in he in eg a ion o he Vi ual Manu ac u ing De ices (VMD) in dis ibu ed sys ems based on CORBA. Mo e explici ly, he MMS e en managemen model has been deal wi h. By means o he Objec Bus de ined in CORBA, making a ailable he MMS e en managemen se ices ha e been achie ed. In o de o accomplish his, he in e ace o hese se ices ha e been buil in id!. S a ing om he da a speci ied in ASN.1 used by he p o ocol, and ollowing he Speci ica ion T ansla ion o The Open G oup, he speci ica ion o hese da a in idl ha e been ob ained. In his pape , he CORBA bases, he MMS and se ices bases a e also explained. 8. ACKNOLEDGEMENT This wo k is suppo ed in pa by he CICYT unde g an num. TAP-95-0307 9. REFERENCES CCE-CNMA, ESPRlT Conso ium (1995). MMS : A Communica ion Language o Manu ac u - ing. Sp inge . CHORUS Sys ems (1996). CHORUS/COOL ORB P og amme 's Guide. CS/TR-96-2.2. G. Guyonne , E. G essie -Soudan, F. Weis (1997). COOL-MMS: a CORBA app oach o ISO- MMS. ECOOP'97 Wo kShop. ISO/IEC. 9506-1 (1990). Indus ial Au oma ion Sys ems -Manu ac u ing Message Speci ica- ion", Pa 1: Se ice De ini ion. In e na- ional S anda ds O ganiza ion. ISO/IEC. 9506-2 (1990). Indus ial Au oma ion Sys ems -Manu ac u ing Message Speci ica- ion ", Pa 2: P o ocol Speci ica ion. In e na- ional S anda ds O ganiza ion. Objec Managemen G oup (1995a). CORBA : Common Objec Reques B oke A chi ec u e and Speci ica ion. OMG, F amingham, MA. Objec Managemen G oup (1995b) . CORBAse - ices: Common Objec Se ices Speci ica ion. OMG, F amingham, MA. Open G oup (1997). In e -domain Managemen : Speci ica ion T ansla ion. X/Open Documen Numbe : P509. Pimen el, Juan R. (1990). Communica ion Ne - wo ks o Manu ac u ing. P en ice-Hal!. Swiss Fede al Ins i ude o Technology, Lausanne (1992). MMS E en Managemen . Compu e Enginee ing Dep .