Xml-based Workflow Engine

Eighth ACIS International Conference on Software Engineering, Artificial Intelligence, Networking, and Parallel/Distributed Computing

The Design and Implementation of XML-based Workflow Engine JIN Xin, XU Jing and LI Xuemeng Institute of Machine Intelligence, Nankai University Nankai University, Tianjin 300071, China [email protected] workflow logic[2,3].

Abstract – This paper brings up a design of XML-based workflow engine and gives an implementation of a web-based

How to control and manage a workflow? This is the main

workflow management system. Workflow is the automation of

content of the conception of Workflow Engine. Workflow

business procedures and workflow engine is the key part to carry

engine offers the environment that a workflow instance need

out the system. Workflow engine can supply the conditions needed

for execution. It can explain the process model, control the

for executing a workflow process. This paper focuses on the

process instances, explore the activities of a process, offer the

workflow

(XML-based

participants to join and exit, build a work to notify the users of

Workflow Process Definition Language) that we designed and the

handling operation, maintain the data of workflow controlling

implementation of the engine. All of the workflow processes that

or some other correlation, evoke other application and access

our engine operates are all described by X-WPDL. The engine

the workflow data[3,6]. Apparent, workflow engine is the only

translates the workflow process into an execution sequence that is

way to implement workflow management.

description

language[1,5]—X-WPDL

consist of events or activities, then loads it in and drives it to run.

Workflow engine should work with an associated

The engine also offers an interface for the manager and participants

workflow description language. This paper also presents a

for interaction. The application case will show that our

XML based description language—X-WPDL. It can describe a

implementation of this engine and the whole system is capable of

workflow very well. According to the grammar of this

processing workflow.

language, our design of the workflow engine has a key module that calls “Node handling Module” for processing that

Index Terms - Workflow; Workflow engine; Workflow

structure “node” that this language defined. Finally, we

management system;

implement the entire workflow management system that has good expandability with a B/S model. It’s already applied in an

1

enterprise that has a great deal of software testing work and

Introduction

implements their office automation of software testing. The or

following of this paper will give a detail description of the

automation of a business process, in whole or part[1]. It is

description method of this system, engine structure etc, and

concerned with the automation of procedures where documents,

analysis on specific examples of the application of this engine.

“Workflow”

is

the

computerized facilitation

information or tasks are passed between participants according

2

to a defined set of rules to achieve, or contribute to, an overall

X-WPDL Description

business goal[3]. In order to achieve this goal by using

The scope of functions that a workflow description

computer technologies, we import the conception “Workflow

language can described is based on the workflow engine. On

Description Language”. Workflow management system is a

the other hand, in order to describe the workflow process better,

system that completely defines, manages and executes

workflow engine has to be adjusted according to the feature of

“workflows” through the execution of software whose order of

description language. Figure 1 shows the effect of X-WPDL in the whole

execution is driven by a computer representation of the

0-7695-2909-7/07 $25.00 © 2007 IEEE DOI 10.1109/SNPD.2007.381

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workflow management system:

to construct a workflow, and a workflow process is the result of the relationship between nodes—this relationship is not only trigger but also depends. After all these analysis have been done on various actual workflow, this paper proposes a workflow description language—X-WPDL. It refers the XPDL[1] of WfMC (Workflow Management Coalition), using XML language and based on the event node, its structure is exactly the same of the workflow process structure which shown in figure 2. So, figure 2 is also the tree of X-WPDL. We will give a detail discuss about node in the following part.

Fig 1 X-WPDL working with the engine

2.2

Definition of node and process

In figure 1, Defined Workflow Process Template (DWPT,

Workflow process definition is based on the conception

it is the definition of process) and Defined Workflow Process

“business process [4] ”and “process definition [4] ”,

Instance (DWPI, it is the application of DWPT) are all

consequently, it should also contain the information such as

described by X-WPDL. Template Definer translates a

“activity”, “connection”, “router”, “participants”, “role” and

workflow process into a DWPT through a special module

“data source” besides some general workflow information. In

interface. When a project starts, Instance Producer will

figure 2, we give a detail description of node structure and its

translate the DWPT into a DWPI according to the content of

effect.

specific work by the way of interacting with workflow engine.

2.2.1 Node Definition

After a project started, the very DWPI will be loaded into the

Node is the basic unit of workflow process; its foundation

engine. DWPI has the same architecture as DWPT because it is

is operation handling. It describes not only the handling way

just the application of DWPT. We separate the two conceptions

and handling content but also all the other information about

because this can improve system safety and give a better

the whole handling, so we can say it’s a “activity” or

understanding to users. 2.1

“event”[5].

Design of X-WPDL

We design the workflow node according to a down-top

How we describe a workflow is more focused on how we

approach: at the bottom is "handling" which is the most basic

describe workflow process. This paper describes the workflow

foundation that describes the specific action including its

process as a node sequence; figure 2 shows the structure of a

operation type, operation message etc; above that, “role” and

workflow process.

“participants” are needed to tell us who will do this handling and what is to be handled. After all this defined, nodes can work well. But, there are several nodes in a workflow; we have to distinguish them, so the nodes need to have their own attributes include “name”, “serial”, “description” and “power” etc. At last, to execute a workflow instance in a correct sequence, nodes must have their dependence or triggering relationship. Therefore, at the top we defined the actions “accept” and “submit” to describe the routing relation between nodes, the former records of all the nodes that this node depends on (the node that must be completed before this node) and the latter records of all the nodes that depend on this node

Fig 2 Workflow Structure

(the node that can only be held after the completion of the

From this chart, we can see that node is the basic structure

node). Apparently, we also define a “data” part in the two

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<X-WPDL:Application>...

actions to record the dataflow between nodes. Following is the X-WPDL description of node: <X-WPDL:Step>

3

<X-WPDL：StepProperty> <X-WPDL: StepName>Notification <X-WPDL：StepDescription>...

The design of workflow engine

This paper designs a multilayer workflow engine. The most important module of the engine is Node Handling

……

Module. It also has a manage module (Workflow Engine

<X-WPDL：StepHandle> <X-WPDL：StepRole>Normal

Manage Module) scheduling among different layers and

<X-WPDL：StepParticipate>...

various groups.

<X-WPDL：HandleType>SENDMESSAGE ……

3.1

Engine structure

We design the engine with four layers: user interface, data

<X-WPDL：Receive>

pretreatment, engine group and system interface. Figure 3

<X-WPDL：RelationStep>

show the structure of this engine.

<X-WPDL：Relation>... <X-WPDL：RelationData>... <X-WPDL：Submit> <X-WPDL：RelationStep> <X-WPDL：Relation>... <X-WPDL：RelationData>...

2.2.2 Process definition

From figure 2, we can see clearly that “process definition” can be expressed as “a start node and a sequence of middle node and an end node”. As we mentioned above, the “depend” and “trigger” relation between nodes is the assurance

Fig 3 Workflow engine structure

to make a workflow works in the correct way. To make a

By using the hierarchical structure, it is more convenient to

integrated business process, the description of workflow

distinguish the core module from other parts and make the main

attributes and the resources it refers are needed in addition.

function of engine low coupling and high cohesion.

Following is the X-WPDL description of workflow process

3.1.1 User interface layer

definition:

This layer is the channel for users to check, manage and

<X-WPDL:Flow> <X-WPDL:Information> <X-WPDL:Name>... <X-WPDL:Serial>... ...... <X-WPDL:Process> <X-WPDL:Start>... <X-WPDL:Step> <X-WPDL:StepName>... ... ... <X-WPDL:End>... <X-WPDL:Resource> <X-WPDL:Form>... ...

use the engine. It includes data interface, management interface and log interface. z

Data interface is a channel for data flow between users and workflow management system. All of the data from the beginning of this project to the end should be transferred through this interface, even the controlling data that the project manager sends.

z

Management

interface

is

used

by

the

system

administrator for checking the state of the engine, controlling the engine to start、 pause、 go on or stop etc. It also does the work that import or export the

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z

WPOR(workflow process of running[3]) data when

Scheduling Module works on the base of the priority of

exception happens.

WPOR. This module gets the most prior WPOR firstly

Log interface is used to record the information about the

and loads its correct node into Node Handling Module.

operation of the engine or the exceptions, bring us a

Node Handling Module is the key part of the whole

convenient way to check and maintain the engine.

engine, and node resource group is tightly corresponding with it. This module follows the controlling information

3.1.2 Data Pretreatment Layer

During the routine of a workflow, the data that user

that come from management module and deals the correct

interactive with the engine are various. In order to upgrade the

node which is Scheduling Module required. It analyses

compatibility of the whole system, we format the data into a

the information of a workflow, sends the users

XML format. This deal greatly enhance the ability of data

appropriate operation, listens the data and controlling that

expressing but increase the difficulty that workflow engine

users send and changes the state or data of a workflow

deal with, this is why we design this layer in the engine. The

followed by the rules.

work this layer does is to change the XML format data into a

3.1.4 System Interface Layer

XML tree object which could be understood by the engine, and

This layer is the interface of workflow engine and the

also transfer the data which the engine export into XML

bottom of the whole system. It is used for the corresponding

format.

database access and file access.

3.1.3 Engine Layer

3.2

Engine operation procedure

This layer is the most important part of the whole engine,

The engine keeps working in the server after its starting

includes: WEMM (Workflow Engine Management Module),

except there is a system exception or someone shut it down. Its

Resource Group, Pretreatment Group and Running Group.

operating is an endless recycling procedure. Node handling

WEMM controls the operation of the engine, monitors the state

process is the most important sub process. Figure 4 shows us

of every module and schedules data resource. It receives and

the engine operating procedure.

analyses data from upper layer interface, then, distributes the data to the other 3 groups according to the data content. z

Resource Group: mainly includes X-WPDL grammar

analysis module and node resource group. The former is used to analyze the XML tree object which we got from data pretreatment layer according to X-WPDL grammar rules, and prove the preciseness of X-WPDL. The latter contains all the resources needed in the process of node design; it offers all the node resources and tables information to construct a workflow instance. z

Pretreatment Group: includes Template-to-Instance Module

and

Instance-to-Object

Module.

The

former

is

Fig 4 Engine operation procedure

responsible for transforming DWPT into DWPI and the

z

z

Check controlling information:

latter is responsible to transform DWPI into WPOR

At the beginning of every loop, the engine should check

(Workflow Process Object for Running) and add it to the

the control information table first, if there were no control info

WPOR queue.

from users at that moment, the engine would get into the

Running Group: includes WPOR queue, Scheduling

instance table and load next instance. Otherwise, it’ll execute

Module and Node Handling Module. WPOR queue

the control order and then get into the instance table.

records all the active workflow instance objects right now

z

Check instance table, get current node:

The engine will load the first instance which is on the top

about their current state and other information.

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of WPOR queue and get the correct node of this instance

4.2

The engine drives the instance to run

according to its status. If the state shows it is an end node, the

When the Instance Producer needs to construct a specific

engine will end this instance; otherwise, the engine should

DWPI of s testing project, first, they interactive with the engine

judge the operation type of this node.

management module through the management interface and

z

Node handling operation

the workflow management system loads the corresponding

First, the engine checks the conditions and the data that

DWPT; second, the system translates the DWPT into a XML

triggered this node; second, the engine executes the operation

tree object by using X-WPDL compiler to build a DWPI; third,

this node described, if the results were succeeded, the engine

they bind the roles with the specific person who should join

“submits” this node, triggers the following node and handles

this work and bind the documentation data with the actual

the correspond data; at last, records the operation above in a log

documents; at last, they starts the DWPI they got and turn it

file.

into a WPOR, add its info into the instance table and load it into

z

Write the operation result in the executive feedback table

the engine to run.

and change the state of this workflow instance. Go back to

After a WPOR was built, the engine works as figure 4

the beginning of this loop.

shown to schedule all the WPOR in the instance table. When

System implementation on the engine

the testing workflow instance is at the first place of this WPOR

Figure 5 shows a testing business workflow. It introduces

module for checking the instance table to get the current node

4

queue and its state is active, the system calls on the scheduling

what role should do what king of operation and what outcome

of this instance and loads it into the node handling module.

is expectant from the beginning to the end of a testing project.

Supposing the current node is “Make Test Plan” and the former is “Distribute Test Task”. The engine will receive the data transmitted from the former node according to the handling this node defined, and sends a message to the project manager telling that the former node has ended.. The manager will check the former node and start the “Making test plan” node and “Build Test Environment” node. At the same time, the engine contacts node resource group getting the specific document of writing test plan for the users to fill. The two nodes will be executed by the engine in turns and whichever has been done it will send a message to its next node. The condition for the node “Testing” to start is that both of the nodes it depends are all finished. This testing project workflow will continue running depend on the relationship between nodes. It deals the nodes one by one until “Handling report” is done, then, this workflow

Fig 5 Test Business Workflow 4.1

instance flow into the tail node “Ending”. When the engine

Workflow Process Definition

handling this WPOR the next time, the appropriate node of this

According to the analysis of this testing workflow,

instance is “End”, and the engine will terminate this instance,

Template Definer sets every step of this work into a node with

update instance table and delete this WPOR from WPOR

joining in the roles on the left and the documentation resource

queue. This is a completed procedure of a workflow

on the right. After all these work have been done, we have got a

processing.

corresponding DWPT which means we finished the process

5

definition.

Conclusion

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In this paper we designed a XML carrier reconfigurable workflow description language, and completed the design of actual business process according to the process definition model. It set the workflow description info refer to the standards of WfMC. Based on these, we designed the correspond tools of language definition, compiler and translator. This paper also designed a workflow engine that separated from the whole workflow management system and operated in the server stably, securely and efficiently. This workflow management system has already applied in actual testing work and run well.

Acknowledgments The research work here is sponsored by Tianjin Science and Technology Committee under contract 043185111-15 and 06YFJMJC00300

Reference [1] WfMC. Wf-XML2.0 .2004 [2] WfMC. Workflow Reference Model. Document Number WFMC-TC00-1003 1995 [3] SHIMeiLin,YANGuangXin,XIANYong,WUShangGuang. WfMS： Workflow management system. Chinese Journal of Computers 1999 Vol.20 No.3 P.325-334 [4] WfMC. Terminology&Glossary. Document Number WFMC-TC-1011 1999 [5] WfMC. Process Defination Interface--XML Process Defination Language. Document Number WFMC-TC-1025 2005 [6] ZHANGHongShen,YINRenKun,ZHANGSuQin. Design of Workflow Engine Based on Web. Computer Engineering 2004 Vol 30 No 4 P83-85

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