Modeling and Validating BPMN Diagrams

Modeling and ValidatingBPMN Diagrams

Michele Chinosi, Alberto Trombetta

Universita degli Studi dell’Insubria (Varese – Italy)Dipartimento di Informatica e Comunicazione

[email protected]

BPMN 2009 WorkshopJuly 20, 2009, Vienna, Austria

Contents Cloud

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Agenda

BPMN 1.1 and 2.0 Analysis

Our BPMN Metamodel Proposal

The XML Linearization

Referential Integrity

Concluding Remarks

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Motivations

• need for easy usable models to test properties, to patch BPMN andto add new features

• other proposals (as well as BPMN 2.0 submissions) are quite unclearand too complex

• lack of validation support

• BPMN 1.1/1.2 comes without a native XSD

• methods to ensure diagrams correctness are manual and error-prone

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Contributions

• simplified test-oriented version of the BPMN metamodel

• self-validating XML serialization for BPMN diagrams

• automated checks (using software tools)

• our approach could be abstracted from the specificities of BPMN1.2 porting the base concepts also to BPMN 2.0

Last-Month Update

This work has been partially superseded by the recent BPMN 2.0 finalsubmission adoption by OMG. We will see a brief summary of majorchanges at the end of this talk.

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Contributions

• simplified test-oriented version of the BPMN metamodel

• self-validating XML serialization for BPMN diagrams

• automated checks (using software tools)

• our approach could be abstracted from the specificities of BPMN1.2 porting the base concepts also to BPMN 2.0

Last-Month Update

This work has been partially superseded by the recent BPMN 2.0 finalsubmission adoption by OMG. We will see a brief summary of majorchanges at the end of this talk.

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BPMN 1.1 Weak Points Analysis

• weak hierarchical structure of the model• BPD are strongly hierarchical• elements placement inside the model does not reflect the expected

placement inside the diagram

• UML metamodel uses only generalization connections• no valid/meaningful instances

• lack of distinctions between several elements and types definitions• they are all elements (classes)• Connections-by-Types

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Sketch of BPMN 1.1 Metamodel

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Different Hierarchical Structures Comparison

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BPMN 2.0 Overview

(B)IOS

• (BEA), IBM, Oracle, SAP

• execution semantics formalization

• extensibility mechanism for both model and graphical extensions

• event composition and correlation refinement

• human interactions definition

• choreography model

BPMN-S

• Adaptive, Axway Software, HP, Lombardi Software, Fujitsu, et al.

• business level modeling

• checking compliance to choreography and rules

• process taxonomies

• execution interoperability

• model re-usability

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Sketch of BPMN 2.0 UML – (B)IOS Proposal

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Sketch of BPMN 2.0 UML – BPMN-S Proposal

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Sketch of BPMN 2.0 UML – Final Submission

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BPMN 2.0 – The CORE UML Class Diagram Example

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BPMN 2.0 – The Package Diagram Example

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Our BPMN 1.1 Metamodel Proposal

• top-down fashion methodology• from BPD to all the other elements• strongly hierarchical model

• reduces the Connections-by-Types and deletes all the missingconnections

• BPMN Supporting elements treated as types• simpler model• Connections-by-Semantics (UML compositions)

• every BPD can be described as one valid instance of the model

• right positioning of Connecting flow objects

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Sketch of our BPMN 1.1 Metamodel Proposal

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BPMN ⊃ WS-BPEL Still incomplete⇒ BPMN 2.0 ⇒ and

BPMN 6= XPDL Complex

BPMN 1.1 → XMLcould be adapted to become−−−−−−−−−−−−−−−−−−−−−→ ⊆ BPMN 2.0

• Our linearization proposal could be useful to study diagram and/ormodel properties and to make some tests, as well as to validate botha model and its instances.

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BPMN ⊃ WS-BPEL Still incomplete⇒ BPMN 2.0 ⇒ and

BPMN 6= XPDL Complex

BPMN 1.1 → XMLcould be adapted to become−−−−−−−−−−−−−−−−−−−−−→ ⊆ BPMN 2.0

• Our linearization proposal could be useful to study diagram and/ormodel properties and to make some tests, as well as to validate botha model and its instances.

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Detailed BPMN 1.1 Weak Points Analysis

Attributes default values

• BPMN defines mandatory attributes WITH default values

• XML-Schema does not permit this double assertion

. if an attribute has the default clause defined, it takes the defaultvalue even if it is not present at all

. use=‘‘optional’’ + default=...

Process

• BPMN defines Processes as conceptual siblings of the BPD

• if a Pool shares a Process, then it has one or more Lanes

• all the other elements are referenced by the Process using their IDs

!! we don’t want a valid instance with Process as root element

. ∃ Process ⇒ ∃ Pool, but ∃ Pool ; ∃ Process

. Process becomes child of Pool

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Process







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Process







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Process







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Participant

• “A Pool represents a Participant”

. Participant is child of Pool

Message

• “A Message is the object that is transmitted through aMessageFlow”

. Message is child of MessageFlow

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Participant

• “A Pool represents a Participant”

. Participant is child of Pool

Message

• “A Message is the object that is transmitted through aMessageFlow”

. Message is child of MessageFlow

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Web Service

• WebService is required by many other elements

• BPMN defines WebService as a Supporting Element

. Inside the BPMN to WS-BPEL mapping example the WebService isdefined inside the parent element

. We chose to instantiate WebService every time it is needed(xs:assert)

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Send Task Definition

1<xs:complexType name="SendTaskType">2<xs:complexContent >3<xs:extension base="bpex:TaskType">4<xs:sequence >5<xs:element name="WebService"6type="bpex:WebServiceType" minOccurs="0">7<xs:assert test="@Implementation=‘Web Service ’"/>8</xs:element >9</xs:sequence >10<xs:attribute name="MessageRef"11type="bpex:ObjectRef" use="required"/>12<xs:attribute name="Implementation"13default="Web Service">14<xs:simpleType >15...

Listing 1: An excerpt of the Send Task definition

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Events

• XPDL and WS-BPEL define for each Event type a different element

• complex XML tree

• BPMN defines only one Event ELEMENT with 3 FAMILIES andmany different TYPES

. families and types are specifications and not different elementdefinitions

. Start, Intermediate and End Event are children of Lane(xs:assert)

. we assign a different type based on the Trigger or Resultattributes values (xs:alternative)

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Event Definition

1<xs:complexType name="LaneType">2<xs:complexContent >3<xs:extension base="bpex:CommonSwimlaneType">4<xs:sequence >5<xs:element name="StartEvent"6type="bpex:StartEventType"7minOccurs="0" maxOccurs="unbounded">8<xs:assert test="@EventType=’Start ’"/>9</xs:element >10...11<xs:complexType name="StartEventType">12<xs:complexContent >13<xs:extension base="bpex:EventType">14<xs:sequence >15<xs:element name="Trigger"16type="bpex:CommonEventDetailType"17minOccurs="0" maxOccurs="unbounded">18<xs:alternative test="@EventDetailType=’None ’"19type="bpex:NoneEventDetailType"/>20<xs:alternative test="@EventDetailType=’Message ’"21type="bpex:MessageEventDetailType"/>22...

Listing 2: An excerpt of the Events definition

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Gateways

• Gateways can only be detailed in one of the five provided types

• there is only one element (Gateway) and five possible specifications

• the Gateway default type is chosen in 2 steps: Exclusive and thenData-Based

. we define only one element of type Gateway, child of Lane

. we decide in a second time the Gateway type usingxs:alternative

. the Gateway default type is chosen in 1 single step: Data-BasedExclusive

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Gateway Definition

1<xs:element name="Gateway" type="bpex:CommonGatewayType"2minOccurs="0" maxOccurs="unbounded">3<xs:alternative4test="@GatewayType=’Data -Based Exclusive ’"5type="bpex:DataBasedExclusiveGatewayType"/>6<xs:alternative7test="@GatewayType=’Event -Based Exclusive ’"8type="bpex:EventBasedExclusiveGatewayType"/>9<xs:alternative10test="@GatewayType=’Inclusive ’"11type="bpex:InclusiveGatewayType"/>12...

Listing 3: An excerpt of the Gateways definition

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Sub-Processes

• Reusable: Activity which re-calls another Process. ProcessRef and DiagramRef

• Reference: it points to another already defined Sub-Process. SubProcessRef

• Embedded: it contains a process dependent from the parent process. the SubProcess elements are defined as Lane children andreferenced using the GraphicalElements attribute

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Artifacts

• one Artifact could be used across the whole BPD, using Associationsto reference elements

• they need only one place to be instantiated

. Artifacts as BPD children

. inside the XML they can be positioned everywhere

Transactions and Signals

• some elements need to be referenced from multiple objects and theyare instantiated every time they are requested: different IDs but thesame name

• the attribute TransactionId of type String serves as an “identifierfor the Transactions used within a diagram”

. we extended the idea behind the TransactionId also to Signalsand other similar objects

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Artifacts

• one Artifact could be used across the whole BPD, using Associationsto reference elements

• they need only one place to be instantiated

. Artifacts as BPD children

. inside the XML they can be positioned everywhere

Transactions and Signals

• some elements need to be referenced from multiple objects and theyare instantiated every time they are requested: different IDs but thesame name

• the attribute TransactionId of type String serves as an “identifierfor the Transactions used within a diagram”

. we extended the idea behind the TransactionId also to Signalsand other similar objects

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Referential Integrity Using XPath

• The very old way: manual ID/IDRef references – strings, numbers,NCNames, random generators, . . .

• The old way: xs:key and xs:keyref

• The new way: xs:assert and xs:alternative

xs:assert

• <xs:assert-test=‘‘XPathExpr’’ />

• limit: the XPath 2.0 expressions set

xs:alternative

• it permits to choose the type of an element according to the successof a XPath 2.0 test

• useful for Events, Gateways, Activities

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Referential Integrity Using XPath

• The very old way: manual ID/IDRef references – strings, numbers,NCNames, random generators, . . .

• The old way: xs:key and xs:keyref

• The new way: xs:assert and xs:alternative

xs:assert

• <xs:assert-test=‘‘XPathExpr’’ />

• limit: the XPath 2.0 expressions set

xs:alternative

• it permits to choose the type of an element according to the successof a XPath 2.0 test

• useful for Events, Gateways, Activities

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Referential Integrity Verification

• Using our XML-Schema Model we are able to validate statically thesyntax as well as structural semantics rules of a BPD

• Using a set of XQuery/XPath interrogations on the XML instanceswe can validate also most of the behavioral semantics rules of BPMN

• The use of XQuery/XPath let us verify business rules at code-gentime and at run-time

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Wrong BPMN Diagram

red: clear (model) errors – orange: hidden (XML) errors

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Parsing the XML Document

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Start Event Check

1for $pool in //Pool ,2$startevent in $pool// StartEvent3return $pool// SequenceFlow[@bpex:TargetRef= ←↩4$startevent/@bpex:Id ]/ @bpex:Id

Listing 4: Rules verification using XPath/XQuery: Start Event

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Events Number Check

1for $pool in //Pool ,2$numSE in count ($pool// StartEvent),3$numEE in count ($pool// EndEvent)4return if ($numSE >0) then5if ($numEE >0) then true() else false()6else7if ($numEE =0) then true() else false()

Listing 5: Rules verification using XPath/XQuery: Events number

“If there is an End (Start) Event, then there MUST be at least one Start(End) Event”

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Instantiation Semantic Verification

1for $pool in //Pool ,2$startEvent in $pool//StartEvent ,3$numSE in count ($ startEvent),4$elements in $pool/Lane /*[ name ()!="StartEvent"]5return6if ($numSE >0) then7if (every $id in $elements/@bpex:Id satisfies ←↩8$id=$pool/SequenceFlow/@bpex:TargetRef)9then true()10else $elements/@bpex:Id11else false()

Listing 6: Rules verification using XPath/XQuery: instantiation semantic

“If the Start Event is used, then there MUST NOT be other flowelements that do not have incoming Sequence Flow”

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Comparison with BPMN 2.0

BPMN 1.1/1.2 BPMN 2.0 Could our proposal bestill valid?

Metamodel Y Y With some changes tobe compliant to theBPMN 2.0 metamodel

XSD N Y With some changesReferential Int. Partially Partially YExecution N Y Y

To have a simplified core subset of both the BPMN metamodel and theXML-Schema, compliant to BPMN specifications, is useful to test someproperties, to implement new features, to attempt new strategies, toimplement patches.

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Conclusions

What we have talked about

. BPMN 1.1 analysis

. BPMN 2.0 metamodel overview

. Our proposal for a BPMN simplified test-oriented metamodel

. Our proposal for a BPMN XML serialization

. Referential Integrity in BPMN: overview and new approach

. Differences between BPMN 1.1 and BPMN 2.0

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Further Works

. We are deeply analyzing both the BPMN 2.0 metamodel and its XSDto get some weaknesses

. We aim to build a tough core subset of the BPMN 2.0 metamodelderiving, as a consequence, a core subset of the XML-Schemaserialization

. We aim to test some properties over this BPMN Core (maybe the sameCore as defined inside BPMN 2.0 specs) adding some new functionalitieslike the validation support at code-gen time.

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Thank you.

Questions?

July 20, 1969 – 22.56 EDT

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Business

Modeling and Validating BPMN Diagrams