levi - project design document

PROJECT DESIGN DOCUMENT

Levi – the Native BPMN 2.0 Execution Engine

Version 1.0

Levi | Project Design Document i

PROJECT SUPERVISORS

Ms. Vishaka Nanayakkara

Dr. Sanjiva Weerawarana

Mr. Milinda Pathirage

GROUP MEMBERS

Index No Name E-mail

070468D Eranda Sooriyabandara [email protected]

070206B Ishan Jayawardena [email protected]

070138R Keheliya Gallaba [email protected]

060501P Umashanthi Pavalanathan [email protected]

Levi | Project Design Document ii

REVISION HISTORY

Date Version Description Authors

12/01/10 Draft Draft version All members

12/02/10 0.9 Pre-final All members

12/03/10 1 Final All members

Levi | Project Design Document iii

TABLE OF CONTENTS

1. Introduction ........................................................................................................................... 1 1.1 Purpose ........................................................................................................................... 1 1.2 Scope .............................................................................................................................. 1 1.3 Document Overview ...................................................................................................... 1 2. Architectural Overview .......................................................................................................... 2

2.1 System Overview ........................................................................................................... 2 2.2 Architectural Representation ......................................................................................... 3 3. Architectural Goals and Constraints ...................................................................................... 3 3.1 Assumptions and Dependencies .................................................................................... 3

3.3 Goals and Guidelines ..................................................................................................... 4 3.4 Development Process ..................................................................................................... 5 4. System Design ....................................................................................................................... 6

4.1 High Level Design ......................................................................................................... 6 4.2 Deployment Design for Business Process Execution in the Process Engine ................. 8 4.3 Class Diagrams .............................................................................................................. 8 5. Use-Case View..................................................................................................................... 13

5.1 Use-Case Realizations ................................................................................................. 13 6. Logical View ........................................................................................................................ 17 7. Process View ........................................................................................................................ 18

8. Development View .............................................................................................................. 19

9. Physical View ...................................................................................................................... 20 4 Supporting Information ......................................................................................................... 21 4.1 Definitions, Acronyms, and Abbreviations ................................................................. 21

4.2. References ................................................................................................................... 22

Levi | Project Design Document iv

TABLE OF FIGURES

Figure No Description Page No 2.1 Example of a private business process ......................................................................................... 4

2.2 Example of a public process ............................................................................................................. 4

2.3 An example of a collaborative process ......................................................................................... 5

2.4 An example of a choreography ........................................................................................................ 6

2.5 An example of a Conversation diagram ....................................................................................... 6

3.1 A simple business process ................................................................................................................. 8

3.2 The Purchaser process and its collaborations with other service provider

processes ................................................................................................................................................. 9

3.3 Incident Management with human-driven and system-driven pools ...........................11

3.4 This rather simple diagram is all we have to show to the account manager .............12

3.5 This is the only part of the whole collaboration we will execute in Levi .....................13

3.6 Multiple outgoing Sequence Flows ..............................................................................................14

3.7 The Lifecycle of a BPMN Activity ..................................................................................................15

3.8 The Parallel Gateway .........................................................................................................................17

3.9 The Exclusive Gateway ......................................................................................................................17

3.1 The Inclusive Gateway ......................................................................................................................18

3.11 The Event-Based Gateway ...............................................................................................................18

3.12 The Complex Gateway .......................................................................................................................29

3.13 Sample Web User Interface for deploying a BPMN process ..............................................26

3.14 Sample Web User Interface for a user to manage his tasks assigned by the

Process Execution Engine ................................................................................................................27

Levi | Project Design Document 1

1. Introduction

1.1 Purpose

This Design Document provides a comprehensive architectural overview of the project Levi -

the native BPMN 2.0 execution engine, using a number of different architectural views to depict

different aspects of the system. This document is intended to capture and convey the significant

architectural decisions about the system to the members of the project team and the

supervisors, both internal and external, who will participate in the implementation phase of the

project and verify the architectural significance of the system. As Levi being an open source

project based on Apache ODE, this document also intends to convey the architectural details of

the project to interested audience and will be made available publicly.

1.2 Scope

Levi is a native BPMN 2.0 execution engine, which can be used to execute business process

models that conform to the BPMN 2.0 specification. And most importantly, it will serve as a

proof of concept for exploring the possibilities of using Apache ODE (Orchestration Director

Engine) and JACOB (Java Concurrent Object Framework) to execute BPMN 2.0 processes. This

engine will be capable of deploying, persisting, navigating, and executing business processes

claiming BPMN 2.0 execution conformance. The major objective of BPMN 2.0 standard is to

provide a high level overview of business processes and their execution to the business people

who do not have much technical expertise. We allow businesses to have automated, efficient

process flows and eventually increase their productivity by facilitating the execution of these

modeled business processes in Levi.

1.3 Document Overview

Section 2 describes the architectural overview of Levi and the method of architectural

representation used in this project design document to present different views of architecture,

which are the aspects of the system in the perspective of different stakeholders. Section 3 briefs

the architectural goals of Levi and the identified constraints; it also has an overview about the

development process to be used to implement the system.

Details about the proposed system design are depicted and described in section 4. System

design is presented using high level design, deployment design and class diagrams. The BPMN

constructs to be implemented in the Levi engine are also identified and depicted as a class

diagram in section 4. Section 5 presents the use case view of the system using use case

realization.

Section 6 to 9 contains the four different views of architecture. These four different views are

explained in the context of this project, using different types of UML diagrams. Section 6

describes the logical view of the system using sequence diagrams and section 7 describes the

process view of the system using activity diagram. A comprehensive package diagram is used in

section 8 to describe the development view of the system and section 9 describes the physical

or implementation view of the Levi business process engine.


2. Architectural Overview

2.1 System Overview

The project Levi is based on Apache ODE with the goal of implementing a native BPMN 2.0

execution engine. The initial version of Levi will serve as a proof of concept for exploring the

possibilities of using Apache ODE and JACOB to execute BPMN 2.0 processes. Figure 1 shows the

high level architecture of Levi engine based on Apache ODE.

The current scope of this project is indicated in figure 1, using dotted lines. Integration layer and

implementation of integrating web services will be added to the system in the later stages. The

input to the system is the BPMN process diagrams and WSDL definitions. An object model is

generated using the OM Model Generator component and the process definition is given as

input to the ODE BPMN runtime. The ODE BPMN runtime component handles the execution of

the input business process using the JACOB framework and data access objects. Process states

are persisted using the persistence capabilities of the JACOB framework.

BPMN Process Definitions, WSDL

Compiled Process Definition

OM Model Generator

ODE BPMN Runtime Instantiation of Processes Implementation of BPMN Constructs Routing of Incoming Messages

ODE Data

Access Objects

JACOB Persistency of Execution States Concurrency Navigation

ODE Integration

Layer

Web Services

DBMS

Figure 1- Proposed Architecture for Implementing BPMN 2.0 Based on JACOB Framework


2.2 Architectural Representation

The 4+1 View model of architecture is used for the purpose of describing multiple aspects of the

system in different stake holders’ perspective. Figure 2 shows the 4+1 view model as a diagram

indicating the stakeholders interested in each view. The four views are logical, process,

development and physical view. In addition use case scenarios are used to illustrate the

architecture serving as the ‘plus one’ view.

3. Architectural Goals and Constraints

The execution model used by Levi consists of different stages where each stage is responsible of

a precise, predefined task. In the initial stages it converts the supplied business process model

into an executable intermediate format that is understandable internally, and then in the final

stage, it executes this model by employing the concepts such as orchestration, choreography

and intermediate web services invocation layer. In addition to that, Levi’s internals are designed

in such a way that it possesses the ability to be expanded to support choreography modeling

conformance, process modeling conformance, better error handling and debugging

methodologies.

3.1 Assumptions and Dependencies It is assumed that the user of Levi will use a suitable editor which complies with BPMN 2.0 modeling conformance, to model a business process in BPMN 2.0, which, in turn, can be fed as the input to Levi.

Levi’s architecture heavily depends on the JACOB framework and other reusable components of Apache ODE, as will be elaborated in the coming sections of this document. Since ODE depends on the Java Runtime, indirectly, Levi will require the user to have the Java Virtual Runtime installed.

Figure 2 - 4+1 View Model of Architecture


3.2 General Constraints

Levi targets the business community, especially business analysts and managers who are

seeking to improve process efficiency and quality of their enterprise. Business users can model

and execute business processes in the areas of Customer Relationship Management, Supplier

Relationship Management, Logistics, Supply Chain Planning, Financial Accounting, Project

Management, Human Resources and others. Since the users are considered as having

considerable experience in the workflow domain, the users are not considered as novice

computer users. As the open source practice, Levi’s source code will be made available to the

public, so the interested developer level users can customize and further enhance the code base

to fit their requirements.

Levi has to have a good security infrastructure. Since this service is used by various people in an

organization, it is required to have a good authorization and authentication system. For

example, tasks that belong to the management should not be exposed to other workers. Also the

outsiders should not be allowed to a system owned by an organization, which may cause a

considerable amount of loss for the organization.

Since this engine is based on Apache ODE and JACOB, ODE’s virtual process machine, there is a

higher risk of inheriting most of the complexities and shortcomings of their architecture. Since

BPEL being the process execution language of Apache ODE, and BPMN 2.0 being that of Levi,

they have many fundamental differences. For instance, BPMN 2.0 XSD makes heavy use of

inheritance, unlike in BPEL. Because of this reason, the existing XSD parser of ODE cannot be

reused. Therefore, it will be required to write an XSD parser for Levi anew.

The BPMN 2.0 standard consists of a number of constructs for business process modeling and

only a subset of that fall into the executable category. Due to this, the project’s scope limits itself

to a proof of concept scenario as only a subset of the executable components will be

implemented. This project is at an experimental level that explores the web services domain and the business

process modeling domain. Hence a considerable amount of research and study has to be carried

out in this project, making the unique challenges of being one of the first native BPMN engines

in the BPM sphere.

3.3 Goals and Guidelines

One can model an executable business process using a BPMN 2.0 modeling tool and execute it in

Levi. When modeling such processes, the person who models the process must consider all the

necessary interactions with external entities (e.g. the service requests that are sent to the

external service providers) and include them in the process definition appropriately, to make

the model executable. However, that level of modeling is not directly indicated with BPMN 2.0

diagrams, rather, that is a responsibility of the editing tool.


3.4 Development Process

Throughout the project, we use an agile development methodology. There are many specific

agile development methods. Most promote development, teamwork, collaboration, and process

adaptability throughout the life-cycle of the project. But, we are not restricted to only one of

those approaches; rather, we are practicing a combination of all these methods in various

extents.

As it is primarily based on iterative and incremental development, where requirements and

solutions evolve through collaboration between stakeholders, we are planning to complete the

implementation of BPMN 2.0 constructs in few iterations, as depicted in figure 3. The initial

simple iteration will cover all the basic constructs, and act as a proof-of-concept for a native

BPMN 2.0 implementation via a process virtual machine.

SIMPLE

SequenceFlow

Task

SubProcess(embed)

ExclusiveGateway

Parallelgateway

StartEvent

EndEvent

DESCRIPTIVE Pool

Lane

MessageFlow

UserTask

Re-usable Subprocess

DataObject

DataInput

TextAnnotation

Association

DataAssocication

DataStore

MessageStartEvent

MessgeEndEvent

TimerStartEvent

TermiateEndEvent

DODAF

Plus 29 elements

COMPLETE

Plus 50 elements

Figure 3 - Iterative Development of BPMN 2.0 Constructs

http://en.wikipedia.org/wiki/Iterative_and_incremental_development


4. System Design

4.1 High Level Design

Figure 4 shows the major building blocks of a BPMN execution engine. The following sections

give a brief description of each major blocks of the system.

4.1.1 Modeling Tool

A business process is modeled using the modeling tool, using the standard BPMN 2.0 constructs

4.1.2 Process Model

Based on the business process modeled using the modeling tool, a process model is generated.

BPMN 2.0 compliant modeling tool produces the process model according to the standardized

XML interchange schema. That means it is possible to create a BPMN model in one tool with

confidence that it can be opened in different tool.

4.1.3 Process Engine

The business process execution engine receives the process model as input and executes the

executable part of the input business process model. Execution sates are persisted in the

process database. Process engine interacts with humans and other applications in order to

execute the business process.

Modeling Tool

Applications

Levi - Process Engine Process

Database

Process Model

Build time

Runtime

Figure 4 - Major Building Blocks of the Levi Process Engine


Figure 5 shows a representation of BPMN 2.0 core and layer structure, the basic principles of

layering that can be composed in well defined ways. The approach uses formalization constructs

for extensibility that are applied consistently to the definition. The additional effect of layering

is that compatibility layers can be built, allowing for different levels of compliance amongst

vendors, and also enabling vendors to add their own layers in support of different vertical

industries or target audiences. In addition, it provides mechanism for the redefinition of

previously existing concepts without affecting backwards compatibility, but defining two or

more non-composable layers, the level of compliance with the specification and backwards

compatibility can be achieved without compromising clarity.

The BPMN specification is structured in layers, where each layer builds on top of and extends

lower layers. The core or kernel includes the most fundamental elements of BPMN that are

required for constructing BPMN diagrams: Process, Choreography, and Collaboration. The Core

is intended to be simple, concise, and extendable, with well defined behavior.

Figure 5 - A Representation of BPMN 2.0 Core and Layer Structure


4.2 Deployment Design for Business Process Execution in the Process Engine

Figure 6 shows the deployment design of the Levi process engine. During deployment, the

process model is translated in to another format which can be executed by the process engine.

Multiple instances of the same process can be created and it is navigated using an imaginary

token flow mechanism. The important intermediate states of the process instances are persisted

to the process engine database for future use.

4.3 Class Diagrams

The core elements of the BPMN 2.0 specification is are sub-packaged as shown in figure 7. The

Core contains three (3) sub-packages:

1. Foundation: The fundamental constructs needed for BPMN modeling.

2. Service: The fundamental constructs needed for modeling services and interfaces.

3. Common: Those classes which are common to the layers of Process, Choreography, and

Collaboration.

<process …>

<sequence>

….

<flow>

….

</flow>

</sequence>

</process>

Instance Cache

….

Model Cache

Navigator

Navigation Logic

Activity Name ID Cond.. …

Control Link Name ID Cond.. …

Activity Instance Name ID Cond.. …

………

Process Engine Database

Deployment

Figure 6 - Deployment Design of the Process Engine


Figure 8 depicts the class diagram, showing the organization of the core BPMN elements.

Figure 8 - Class Diagram Showing the Organization of the Core BPMN Elements

Figure 7 - Class Diagram Showing the Core Packages


The following class diagrams represent the major classification of major BPMN 2.0 constructs, Event, Gateway and FlowElement. Figure 9 shows the Event class diagram and figure 10 shows the FlowElement class diagram.

Figure 9 - Event Class Diagram

Figure 9 - FlowElement Class Diagram Figure 10 - FlowElement Class Diagram


Figure 11 shows the Gateway class diagram.

Figure 11 - Gateway Class Diagram

Figure 12 and Figure 13 represents the class diagram for the core of the Levi engine, including

the major BPMN 2.0 constructs to be implemented. This class diagram serves as an overview of

the implementation of Levi engine.

Figure 12 - Class Diagram of BPMNRuntime in Levi


Figure 13 - Class Diagram of Levi


5. Use-Case View A description of the use-case view of the software architecture. The Use Case View is important input

to the selection of the set of scenarios and/or use cases that are the focus of an iteration. It describes

the set of scenarios and/or use cases that represent some significant, central functionality. It also

describes the set of scenarios and/or use cases that have a substantial architectural coverage (that

exercise many architectural elements) or that stress or illustrate a specific, delicate point of the

architecture.

5.1 Use-Case Realizations

Figure 14 depicts the use cases in the system for the Actors 'User' and ‘Super User’ in a generic

scenario of working with Levi. In a typical business environment, management will model and deploy

business processes for monitoring, managing and helping out employees’ daily chores.

Figure 14 - Generic Use Case Diagram of Levi


Figure 15 is the use case diagram for automating the incident management process, we

discussed in the System Requirement Specification to be executed in a process engine.

Figure 15 - Sample Use Case for Automated Incident Management System


An e-tender (the "Purchaser" process) which sends a request for quote to multiple service

providers (e.g., warehouse storage) in a marketplace was also discussed in the System

Requirement Specification. It sends out requests to each service provider and anticipates their

response through three Choreography Activities. Figure 16 show its use case diagram.

Figure 16 - Sample Use Case Diagram for 'e-tender' Purchase Application


“Post a Job” use case discussed in the previous document includes the business department and the human resources department. The process starts when an employee is required. The business department reports this job opening. Then the human resources department writes a job posting. The business department reviews this job posting. It is depicted in figure 17.

Figure 17 - Sample Use Case for Job Posting Application


6. Logical View

System sequence diagrams in this chapter illustrate how certain tasks are done between users

and components in Levi, Native BPMN execution engine. These tasks may include repetitive,

simple, or complex tasks. The purpose is to illustrate the use case in a more clear visual format

for the reader. In figure 18, how a super user logs into the system and does basic tasks like

deploying and starting processes is depicted.

Figure 18 - Sequence Diagram for Generic Process Deployment

http://en.wikipedia.org/wiki/Use_case


7. Process View Activity diagram in this chapter illustrate how an example business process execute in Levi, Native BPMN execution engine, which represent workflows of stepwise activities and actions with support for choice, iteration and concurrency. The figure 19 shows a private process of producing an advertisement done by an advertising agency. This activity diagram contains the detailed process which contains number of activities and loops which are not relevant to the customers of the agency such as archiving, reviewing and reworking. The customers are only involving in Ordering including text for the advertisement and confirm whether the advertisement is satisfy their needs, which are shown here as the message flows.

Figure 19 - Activity Diagram Depicting Sample Process Deployment and Execution

http://en.wikipedia.org/wiki/Workflow


8. Development View

The development view illustrates the system from the perspective of the stakeholders who

design and implement the system, the project team and the supervisors in this case. UML

package diagram is used to represent the development view.

Figure 20 shows the different packages which will be used for implementation. The package

“org.levi.bpmn” will contain the sub packages, Java classes and configuration files used to build

the Levi engine. It uses the external packages “org.apache.ode.jacob” and “omg.spec”; JACOB

framework resides in the “org.apache.ode.jacob” package is the base for implementation of Levi

engine; “omg.spec” package contains the schematic representation of BPMN 2.0 constructs and

it is used for the purpose of building the object model from the BPMN 2.0 process model.

Figure 1 shows the component structure of the proposed architecture for Levi engine and it is

useful for the perspective of the development team of the project. It shows each component of

the system and section 2.1 describes each of them.

Figure 20 - Package Diagram Showing Implementation View


9. Physical View

Figure 21 depicts a BPMN process engine deployment in a real world enterprise. Different roles

can be assigned for employees of different departments with different privileges such as

deploying a process, starting a process, assigning tasks, claiming tasks and claim completion of

tasks. Levi engine can be deployed in a distributed environment; it also can be integrated with

existing cloud infrastructure to add more reliability and availability with less cost.

Figure 21- BPMN Process Engine Deployment in a Real World Enterprise


4 Supporting Information

4.1 Definitions, Acronyms, and Abbreviations

BPMN 2.0 : Business Process Model and Notation version 2.0 beta

BPDM : Business Process Definition Metamodel

BPEL : Business Process Execution Language

BPEL4People : WS-BPEL Extension for People

BPM : Business Process Modeling

UML : Unified Modelling Language

RDF : RDF Vocabulary Description Language 1.0

SOAP 1.2 : Simple Object Access Protocol

UDDI : Universal Description, Discovery and Integration

URI : Uniform Resource Identifiers

WSBPEL : Web Services Business Process Execution Language

WSDL : Web Services Description Language

XML : eXtensible Markup Language

XPath : XML Path Language

XSD : XML Schema Definition


4.2. References [1] BPEL Vs BPMN2.0 Should you care? By Prof. Frank Laymen at 2nd Intl. Workshop BPMN 2010, 28th Nov. 2010, http://www.slideshare.net/bpmn2010/frank-leymann-bpmn-2010 [2] Creating Use Case Diagrams, 29 Nov. 2010, http://www.developer.com/design/article.php/10925_2109801_2/Creating-Use-Case-Diagrams.htm [3] Principles behind the Agile Manifesto, 30 Nov. 2010, http://www.agilemanifesto.org/principles.html [4] Sequence Diagram in UML, 2 Dec. 2010, http://www.developer.com/design/article.php/3080941

[5] T. Allweyer, BPMN 2.0 - Business Process Model and Notation, BoD, 2010.

[6] M. Havey, Essential business process modeling, O'Reilly Media, Inc., 2005.

[7] Business Process Model and Notation (BPMN) Specification, Version 2.0 - Beta 2, May 2010 http://www.omg.org/spec/BPMN/2.0/

[8] OMG Group, “BPMN 2.0 by Example,” OMG Group, vol. 0, May 2010. http://www.omg.org/spec/BPMN/2.0/examples/PDF

[9] Bruce Silver. “BPMN 2.0 Status Update”, blog, 5 Oct. 2010, http://www.brsilver.com/2009/07/06/bpmn-20-status-update-2/

[10] BPEL 2.0 Standard, 5 Oct. 2010, http://docs.oasis-open.org/wsbpel/2.0/wsbpel-v2.0.pdf

[11] OASIS, 5 Oct. 2010, http://www.oasis-open.org

[12] BPM FAQs, 5 Oct. 2010, http://www.bpmodeling.com/faq

[13] ODE-793, 5 Oct. 2010, https://issues.apache.org/jira/browse/ODE-793

[14] ODE-794, 5 Oct. 2010, https://issues.apache.org/jira/browse/ODE-794

[15]Process Modeling Notations and Workflow Patterns, paper by Stephen A. White of IBM Corporation (2006) http://www.bpmn.org/Documents/Notations_and_Workflow_Patterns.pdf

[16] Decker, G., Kopp, O., Leymann, F., Weske, M.: BPEL4Chor: Extending BPEL for modeling choreographies. In: ICWS 2007, IEEE Computer Society (July 2007)

[17] Wohed, P., WMP van der Aalst, M. Dumas, AHM ter Hofstede, and N. Russell: On the Suitability of BPMN for Business Process Modelling. Technical report, Queensland University of Technology (QUT), http://www.bpm.fit.qut.edu.au/projects/babel/docs/BPMN-eval- BPM06.pdf, 2006.

[18] Russell, N.: Workflow Resource Patterns. Beta, Research School for Operations Management and Logistics, 2005.

http://www.slideshare.net/bpmn2010/frank-leymann-bpmn-2010

http://www.developer.com/design/article.php/10925_2109801_2/Creating-Use-Case-Diagrams.htm

http://www.developer.com/design/article.php/10925_2109801_2/Creating-Use-Case-Diagrams.htm

http://www.agilemanifesto.org/principles.html

http://www.developer.com/design/article.php/3080941


[19] Russell, N., W.M.P. van der Aalst, A.H.M. ter Hofstede, and D. Edmond: Workflow Resource Patterns: Identification, Representation and Tool Support. Proceedings of the 17th Conference on Advanced Information Systems Engineering (CAiSE 05), 3520:216–232.

[20] Kloppmann, M., D. Koenig, F. Leymann, G. Pfau, A. Rickayzen, C. von Riegen, P. Schmidt, and I. Trickovic: WS-BPEL Extension for People– BPEL4People. Joint white paper, IBM and SAP, July, 2005.

[21] Wohed, P., WMP van der Aalst, M. Dumas, AHM ter Hofstede, and N. Russell: Pattern-based Analysis of BPMN-An extensive evaluation of the Control-flow, the Data and the Resource Perspectives. BPM Center Report BPM-05-26, BPMcenter. Org, 2005.

[22] Aalst, WMP van der and A. Kumar: A reference model for team-enabled workflow management systems. Data & Knowledge Engineering, 38(3):335– 363, 2001.