Group Title: Department of Computer and Information Science and Engineering Technical Reports
Title: Flexible inter-enterprise workflow management using E-services
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Title: Flexible inter-enterprise workflow management using E-services
Series Title: Department of Computer and Information Science and Engineering Technical Reports
Physical Description: Book
Language: English
Creator: Meng, Jie
Krithivasan, Raja
Su, Stanley Y. W.
Helal, Sumi
Publisher: Department of Computer and Information Science and Engineering, University of Florida
Place of Publication: Gainesville, Fla.
Copyright Date: 2002
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Flexible Inter-enterprise Workflow Management using E-Services

Jie Meng, Raja Krithivasan, Stanley Y. W Su and Sumi Helal

Database R&D Center
Department of Computer and Information Science and Engineering
University of Florida, Gainesville, FL 32611-6125, USA

{jmeng, rkrithiv, su, helal}


This paper presents a solution to achieve dynamic Inter-enterprise I I nt, ,li i management using

the e-services provided by collaborative e-business enterprises. E-services are distributed services that

can be accessed programmatically on the Internet, using SOAP messages and the HTTP protocol. We

categorize e-services according to their business types and manage them in an UDDI-enabled Broker

Server. By E-service requests are specified in the activities of a process model according to some

standardized e-service templates and are bound to the proper service providers at run-time by using a

constraint-based, dynamic service binding mechanism. The -ii,, l, k1n management system is dynamic in

the sense that the actual business organizations that take part in a business process are not determined

until run-time.

1. Introduction

In the highly competitive and rapidly changing global economy environment, business

organizations need to collaborate to achieve common business goals in a more flexible and effective way

than ever before. Recently, the use of workflow technology to manage e-businesses has drawn much

attention in the academic community [Alo99, LazOl, Gre99, StrOO, She99]; however, a good solution to

support dynamic workflow management for e-business is still missing.

Business organizations across the Internet have different resources and provide manual and

automated services for the manipulation and access of these resources. To conduct ajoint business

venture, an inter-enterprise workflow management system is needed to integrate data resources, workflow

processes, and services provided by collaborative business organizations. Since business organizations

can enter and leave the Internet world freely, their memberships in a virtual enterprise and their services

may change from time to time. The dynamic nature of services and their providers requires that service

requests specified in a process model be dynamically bound to services at the time when an instance of

the process model is in execution.

We have designed and are implementing a dynamic workflow management system to support e-

businesses [MenO1, HelOlb]. The system is active, adaptive, and flexible. By integrating the system with

an Event-trigger-rule Server and an Event Server [Lam98, LeeOO, SuOO], the enactment of a workflow

process may post events to trigger the processing of business rules to enforce security and integrity

constraints, business policies, and regulation, etc. These rules may in turn activate other workflow

processes, thus making the workflow management system an active system. The triggered rules may also

modify process models at run-time to adapt the models to the changing business situations. This paper

focuses on the flexible aspect of the workflow management system. It presents a mechanism for

dynamically binding e-service requests, which are specified in the activities of a process model, to the

proper e-services and e-service providers.

We define an e-service as "any service or functionality that can be accessed by a business or a

consumer programmatically over the Internet by using a standard service specification and a standard

communication protocol". E-service templates, which are used to standardize the specifications of e-

services, are stored and maintained by a Broker Server. Business organizations register the e-services

they provide with the Broker Server according to the e-service templates, and the service specifications

are also managed by the Broker Server. The activity definitions in a process model contain one or more

e-service requests, which are specified according to the e-service templates and are bound to the proper

service providers at run-time by a dynamic service binding mechanism. Changes in the membership of a

virtual enterprise (i.e., its service providers) will not affect the process models. Thus, the workflow

system has the flexibility of bounding service requests to the available and suitable services and service


In this work, we allow e-service requests to be specified in workflow activity specifications; an

extension to the traditional workflow process specification. We also introduce constraint definitions in

both e-service specifications and e-service request specifications; an extension to the Web Service

Description Language [ChrO 1]. These constraints are used by the Broker Server to do constraint-based

matching of e-service requests with e-service specifications. Another new concept introduced in this

paper is the specification of restrictions on the selection of providers (or performers) by taking into

consideration the interdependencies among activities in a process model.

The organization of this paper is as follows. In Section 2, the architecture of the dynamic

workflow management system is introduced. The e-services and the modeling of workflow processes

based on e-services are introduced in Section 3. In Section 4, we introduce the constraint-based dynamic

service binding mechanism. Section 5 describes the implementation. Section 6 summarizes our research.

2. System Architecture

The architecture of the dynamic workflow management system is shown in Figure 1.

Dynamic WfMS

ETR Server Event Server
Workflow Server
Process Workflow
Definition Tool Engine
Broker Server


E-Service Adapter
E-Service Adapter E-Service Adapterervice

Se ices Services i Servi

Figure 1: Architecture of the dynamic workflow management system.

Business organizations across the Internet can perform and contribute different manual or

automated tasks, which are useful for the operation of a joint business. An E-Service Adapter needs to be

installed at each organization's site to wrap the underlying services, which can be implemented in

different ways, as e-services. Thus, these services can be made accessible on the Internet using SOAP

[BoxOO] and HTTP protocol. A Broker Server works as a central repository for e-services and is typically

used by the service requesters to find required e-services [HelOla]. The Workflow Server is composed of

two sub-components: namely, the Process Definition Tool and the Workflow Engine. The Process

Definition Tool is responsible for modeling business processes, which integrate the e-services across the

Internet. The Workflow Engine schedules the enactment of business processes according to the defined

process models.

The Event Server and the Event-Trigger-Rule (ETR) Server, which give the workflow

management system its active and adaptive properties [MenO1], are also shown in Figure 1.

3. E-Services and Process Modeling

3.1 E-Service Template

In order to introduce a standard way to define e-services, it is useful to categorize e-services and

their providers by the types of business in which these providers are involved. For example, some

business organizations may function as the Distributor of a supply chain. For each business type, a set of

useful e-services can be defined. Business organizations that are of the same business type may provide

all or some of these e-services. The categorization of service providers and the specification of e-services

are consistent with the Universal Description, Discovery and Integration (UDDI) specification [AriOO].

To standardize the specification of an e-service, an e-service template can be jointly defined by

those business organizations of the same business type. An e-service template consists of one or more

operations offered by the e-service. For each operation, there are three types of attributes:

Input attributes, which specify the data needed as input to invoke an operation.

Output attributes, which specify the returned data of an operation.

Service attributes, which specify other properties of an operation, such as the length of time the

operation takes, the side-effect of the operation, etc.

An e-service template can also contain service attributes for the e-service. These attributes

specify the properties of an e-service, such as the cost for using the e-service, the quality of the e-service,

etc., which may be useful for negotiation, contracting, or service selection.

A simple example of an e-service template of an e-service OrderProcessing provided by the

business type Distributor is shown in Table 1. It contains an operation Process Order.

Table 1. E-Service Template of e-service OrderProcessing of Distributor
Service Operations Description
Process Order Name Type
Operations Input Attributes productDesc ProdDesc
quantity Int
userInfo UserInfo
Output Attributes satus Status
Service Attributes duration Time
cost Float
3.2 E-Service Constraint

A service provider registers its e-services with the Broker Server by first browsing and selecting

the proper e-service templates that are managed by the Broker Server. During the registration, the service

provider first provides the Broker Server with its general information, such as its name, URL, telephone,

email, etc. It then specifies the e-services it provides. For each e-service, the service provider needs to

specify the e-service binding description, which contains the location of the service implementation and

details on the protocol and the port to be used to access the server that hosts the e-service.

The service provider can also specify the constraints on the service attributes of the e-service, and

the constraints on the input attributes and service attributes of the operations. By allowing attribute and

inter-attribute constraints associated with e-service and its operations as well as e-service requests to be

explicitly specified, we can extend the Web Service Description Language (WSDL) to increase its

expressive power. These constraints restrict the selection of proper e-service providers for e-service


For constraint specifications, we adopt the syntax and semantics of the Constraint-Based

Requirement Specification Language used in [SuOl]. We shall call these constraints e-service

constraints. For example, a distributor named Worldwide who provides the e-service named

OrderProcessing may specify the following constraint on the operation Process Order as shown in Figure

2. This constraint specification states that the operation Process Order of e-service OrderProcessing can

only process the order of computer product with the quantity less than 1000. If the quantity of the order is

larger than 500, this e-service needs to take more than 10 time units. Iacl is the name of the inter-

attribute constraint.

productName String ENUMERATION ["Computer"] priority[l]
modelName String ANY priority[2]
quantity Integer RANGE [1-1000] priority[3]

lacl quantity > 500 implies duration>10

Figure 2: Constraint specification for operation Process Order.

For each e-service, the e-service template, the e-service binding description, and the e-service

constraints defined by the service provider together form the e-service specification. After registration,

the general information of the service provider and the e-service specifications of the e-services it

provides are stored in a persistent store and managed by the Broker Server.

3.3 E-Service Request and its Constraint

In our dynamic workflow management system, e-service requests are the main task items that can

be specified in an activity definition. They are defined according to their corresponding e-service

templates. The bindings of e-service requests to specific service providers occur at run-time when the

available providers are known to the workflow management system through the Broker Server. During

process modeling, the model designer first browses the e-service template information provided by the

Broker Server. He/she then defines the e-service requests in the activities of a process model according to

the corresponding e-service templates. In an e-service request, in addition to the values of the input

attributes of the requested operation, the constraints on the service attributes of the operation and the e-

service can also be specified. We shall call the constraints in an e-service request e-service request

constraints. An example of an e-service request constraint for the operation Process Order of the e-

service OrderProcessing is shown in Figure 4. It states that the requester expects that the Process Order

operation should not take more than 10 time units, the cost of the e-service should not be more than

$1,000, and if it takes more than 4 time units, then the cost must be less than $800.

duration int RANGE [0 .. 10] priority[l]
cost float RANGE [0.. 1000] priority[2]

iacl: duration >4 implies cost < 800

Figure 3: A sample specification of an e-service request constraint.

In summary, at build-time, the service providers register their e-services with the Broker Server

according to these e-services' corresponding templates. The e-service specifications are maintained at the

Broker Server site. The process model designers define e-service requests according to the same

corresponding e-service templates. The build-time relationship among the Broker Server, the service

providers, and the process definition tool is shown in Figure 4.

E-Service EService Server
Specification Template

/ register reference'

Service / Process Model
Provider Designer

E-Service Adapter Services

Figure 4: Build-time relationship among the Service Provider, the Broker Server, and the Process
Definition Tool.

3.4 E-Service Invocation

The E-Service Adapter at each organization's site wraps services, which have been implemented

in different ways, so that these services can be invoked using SOAP messages that are sent through the

HTTP protocol, according to the format of the corresponding e-service templates. The E-Service Adapter

thus hides the heterogeneity of service implementations and presents a uniform view of these services as

e-services. During the e-service invocation, the E-Service Adapter parses the SOAP message from the e-

service requester (in our case, the Workflow Engine) and determines the operation of the e-service to be

invoked. The E-Service Adapter then determines the corresponding method of different service

implementations, builds the parameter list as required by the method, and invokes the method. After the

invocation is complete, the E-Service Adapter encapsulates the return data into a SOAP message and

returns it to the e-service requester. The SOAP message that is used to invoke the operation

ProcessOrder of the e-service OderProcessing is shown in Figure 5.

3.5 Process Modeling using E-Services

A process model consists of activities that are connected by conditional transitions, which specify

the control flows. Additionally, we add data flows among activities. We shall describe only the activity

definition below because activity is the main modeling construct in a process model and contains e-

service requests. The syntax of the activity specification is shown below.

[WF_EVENTS] workfloww event list>





order shipped


Figure 5: SOAP messages for invocation of operation ProcessOrder in e-service OrderProcessing.
(A) SOAP request message. (B) SOAP response message.




DB Center
CSE470, University of Florida, Gainesville, FL

The activity id is a unique identifier for the activity in the extent of a process model. The

DESCRIPTION clause contains the description of the activity. The input/output parameters of the

activity, which are defined in the IN_PARAMETER/OUTPARAMETER clauses, specify the

input/output data of the activity. The ACTIVITY_VAR clause defines the variables that can be used

inside the activity body. The WFEVENT clause specifies the events that this activity posts. The

explanation of workflow events is beyond the scope of this paper.

The PERFORMER clause specifies the business type of the business organization whose e-

services are requested in the activity. The performer selection constraint in the PERFORMER clause is

defined to further restrict the selection of an organization as the service provider. There are four types of

performer selection constraints as shown below. The last two types take into consideration the

interdependencies between activities in the selection of providers for their e-service requests.

(1) The performer is a particular organization specified by the name of the organization. An example

definition is shown below. Here, Distributor represents the business type of organizations that

provide services as distributors, and worldwide is the designated distributor.

PERFORMER Distributor (CONSTANT worldwide)

(2) The performer can be any suitable organization of the specified business type. In this case, the e-

service requests in the corresponding activity definition will be dynamically bound to a proper

organization at run-time in a dynamic service binding process. An example of the PERFORMER

clause is shown below.

PERFORMER Distributor (ANY)

(3) The performer of the activity should be the same as that of another specified activity. An example

definition is shown below. Here, Activityl is the name of another activity.

PERFORMER Distributor (SAME_AS Activityl)

(4) The performer of the activity is specified by the output parameter of a specified activity. An example

definition is shown below. The performer of the current activity is computed by Activity2 and

represented as the output parameter bestDistributor.

PERFORMER Distributor (VARIABLE Activity2.bestDistributor)

The IMPLEMENTATION clause specifies the activity body, which contains a set of task items of

this activity. The e-service requests are the main task items in an activity body. An activity may contain

several e-service requests, while all these e-services are to be provided by the same business organization.

The e-service request definition is shown inside the activity definition. E-service name is the

name of the e-service to be requested, and operation name is the name of the operation to be invoked.

The in attributes mapping in the INPUT clause represents the mapping between the activity data

(namely, input parameters of the activity and activity variables) and the input attributes of the e-service

request. The mapping between the activity data (namely, output parameters of the activity and activity

variables) and the output attributes of the e-service request is represented by the out attributes mapping

in the OUTPUT clause. The CONSTRAINT clause specifies e-service request constraints.

In addition to e-service requests, there can be two more kinds of task items in an activity

definition: in-line code and event posting. Programming code can be included in the activity definition to

do some computation. An activity can also explicitly post events. Remote systems that have subscribed

to the events will receive event notifications, which report the execution milestones of a process model.

A sample activity definition, which is used to make an order from a distributor, is given in Figure

6. The only task item in this activity is an e-service request to the operation ProcessOrder of the e-

service OrderProcessing. Since the performer selection constraint of this activity is ANY, the e-service

request in this activity will be dynamically bound to a proper distributor during the execution of a

workflow instance initiated from the process model, which includes this activity.

4. Constraint-based Dynamic Service Binding

4.1 Broker Server and Constraint-based Brokering Service

An important function of the Broker Server is to do constraint-based brokering and service

provider selection. In the dynamic workflow management system called DynaFlow, this function is used

by the Workflow Engine to do the dynamic service binding. To achieve this, the Broker Server would

match an e-service request with the e-service specifications given by service providers to identify the

proper service providers) for the request. The data provided for the input attributes of the requested e-

service operation and the constraints specified in the request will have to be compatible with (i.e., not

conflict with) the attribute constraints and inter-attribute constraints specified by a service provider. The

constraint matching is accomplished by using a Constraint Satisfaction Processor (CSP) used in the

system reported in [SuO ].

ACTIVITY Process Order
DESCRIPTION "Process an order from a retailer".
INPARAMETERS String prod name, String model name, Integer quantity,
UserInfo user info
OUT PARAMETERS Boolean order status
PERFORMER Distributor (ANY)

E-SERVICE OrderProcessing.ProcessOrder
INPUT prod name, model name, quantity, user info
OUTPUT order status
duration Integer RANGE [0.. 10] priority[l]
cost Float RANGE [0..1000] priority[2]

lacl: duration > 4 implies cost < 800


Figure 6: A sample activity definition.

In a matching operation, there are three possible results. First, the Broker Server cannot find a

service provider that can provide the e-service that satisfies the constraints and input data given in the e-

service request. In this case, the matching operation has failed. Second, there is a single service provider,

which provides the e-service that satisfies all the requirements of the e-service request or matches the

requirements within an acceptable threshold. In this case, the matching operation succeeds and the e-

service of the provider is used to service the request. In the third case, multiple service providers can

satisfy the request. A Cost-Benefit Evaluation Server [SuOl] is then used to evaluate and rank the e-

services provided by these service providers and the best provider is selected.

4.2. Dynamic Service Binding

The Workflow Engine accomplishes the dynamic service binding with the help of the Broker

Server, which performs the constraint-based service provider selection. Before the Workflow Engine

calls the Broker Server, some preprocessing work needs to be done to determine which e-services

requested in the process model need to be provided by the same service provider. For example, the

provider that processes a purchase order should also handle the shipping of the product and the issuing of

an invoice.

In addition to the attribute constraints and/or inter-attribute constraints that are defined on the

service attributes of an e-service operation during the process modeling, an e-service request constraint

should also contain the input data of the requested e-service operation as attribute constraints. These

values are obtained at the run-time before the e-service operation is to be invoked, and are added to the

original e-service request constraint to generate a new one. A new e-service request constraint of the

operation ProcessOrder of the e-service OrderProcessing is shown in Figure 7.

duration Integer RANGE [0.. 10] priority [1]
cost Float RANGE [0.. 1000] priority [2]
productDesc.prodName String EQUAL "Computer" priority [0]
productDesc.modelName String EQUAL "Pentium 800" priority [0]
quantity Integer EQUAL 500 priority [0]
userlnfo.userName String EQUAL "DB Center" priority [0]
userlnfo. address String EQUAL I ',\ ..'. f ofFlorida, Gainesville, Florida" priority [0]
userlnfo.zipCode Integer EQUAL .';11" priority [0]

iacl: duration >4 implies cost < 800

Figure 7: A new e-service constraint by adding the input data of the e-service operation.

The new e-service request constraint, along with the information about e-services that need to be

provided by the same service provider, is given to the Broker Server to select the proper service provider.

The Broker Server first gets the service providers that provide all the e-services requested from the same

service provider. It then selects the proper one from them using the constraint-based service provider

selection mechanism discussed above.

5. Implementation

We have implemented a prototype of the dynamic workflow management system. The Process

Definition Tool [XiaOl] is a user-friendly graphical editor that can be used to specify the diagram of a

business process model and the details of e-service requests. When using the Process Definition Tool to

define a process model, the process model designer needs to make use of e-service templates, which are

accessible from the Broker Server, to specify e-service requests inside activities. To facilitate the process

modeling in our implementation, we store these e-service templates in a Metadata Manager implemented

for another project [LeeOO]. The screen layout of the Process Definition Tool is shown in Figure 8.

*e ftr. h cId o

Figure 8: The screen layout of the Process Definition Tool.

The Workflow Engine is responsible for scheduling the execution of a workflow instance based

on the process model. When an activity is scheduled for execution, if there are e-service requests inside

the activity and the performer selection constraint of this activity is ANY, the Workflow Engine would

contact the Broker Server to select a proper service provider for the e-service requests inside the activity

in a constraint-based dynamic service binding process. The implementation of the constraint-based

Broker Server is being carried out by extending the Constraint Satisfaction Processor and the Cost-benefit

Evaluation Server used in an automated negotiation system [SuOOa, SuOl]. To invoke an e-service, the

Workflow Engine generates a SOAP message, which contains the e-service request information and send

the message to the E-service Adapter of the selected service provider. The interactions among the

Process Definition Tool, the Workflow Engine, the Broker Server, and E-Service Adapter are shown in

Figure 9.

Workflow Server

WF Engine Definition Tool

Invoke / Set Browse e-servce
sei ,es providers templates


E-Service Adapter Broker Server

Figure 9: Interactions among Workflow Server, Broker Server and E-Service Adapters

6. Conclusion

This paper presents a solution to achieve flexible inter-enterprise workflow management in an e-

service infrastructure. In this infrastructure, providers of e-services register their services with a Broker

Server based on standard templates pre-defined for different business types. The service requests

specified in the activities of a workflow process model can be dynamically bound to these distributed e-

services and their providers with the help of the Broker Server. E-service requests posed in XML SOAP

messages can be sent to the identified provider sites through the HTTP protocol. We have extended the

traditional workflow process modeling by including e-service requests in activity specifications and

extended e-service specification proposed by WSDL by including constraint specifications so that the

selection of e-service providers can be more accurately performed. The constraint-based dynamic e-

service binding mechanism presented in this paper allows inter-enterprise workflow process models to be

processed in the Internet environment, in which business organizations and their services are changing

constantly. The interdependencies among activities of a process model with respect to provider (or

performer) selection are also considered.

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