COMPONENT-BASED MODELLING OF ORGANISATIONAL

RESOURCES USING COLOURED PETRI NETS

Khodakaram Salimifard

Department of Industrial Management, Persian Gulf University, Booshehr 75168, Iran

Keywords: Workflow, Organisational Modelling, Coloured Petri Nets, Component-based Modelling

Abstract: Collaborative software applications such as workflow management systems require a clear separation

between process model and resource model. The process model realises the partial order of business

processes while the organisation model provides the structure of the resources to be utilised. In this paper,

we propose a CPN-based framework for modelling organisational functioning units. The models are

developed independent of the process layer. Maintaining the flexibility and scalability, the model, hence, is

capable to be modified without altering the process model.

1 INTRODUCTION

The term “workflow modelling” implies the

requirement to represent the processes through

which the work is accomplished. This requirement

becomes a vital issue in designing and re-designing

a workflow system. A workflow model defines what

has to be done. That is, it represents a functional

perspective (Koulopoulos, 1995). On the other hand,

the model frames the behavioural and organisational

perspectives (Jablonski et al., 1996). Many of the

existing approaches to workflow modelling are

based on using Petri nets (Ellis et al., 1993)

(Ferscha, 1994) (Aalst, 1998) (van He et al., 2000)

(Salimifard and Wright, 2001). The standardisation

of model elements has captured less attention,

although the compositionality of Petri nest has been

discussed in (Voorhoeve, 2000). Recently, the

requirements for modelling workflow have been

investigated (www.minicom,com). The requirements

have been classified into modelling patterns

representing comprehensive functionality necessary

for workflow software. In this paper, we introduce a

CPN-based compositional approach for modelling

workflow processes and organisational units.

2 MODELLING REQUIREMENTS

The behavioural perspective (Koulopoulos, 1995) of

a workflow is represented by control flows (Aalst,

1998). A control flow specifies the execution order

(Jablonski et al., 1996) and dependencies between

workflows. It determines all the possible execution

orders of embedded workflows. A control flow

construct is either an elementary or composite. A

composite control flow construct is a composition of

the other control flow constructs. This hierarchical

representation allows the workflow designer to

design a complex workflow using a set of control

flow constructs.

In order to have a standard definition, a formal

specification of the semantics of control flow

constructs is required. The formal definition makes

it possible to validate the proposed constructs and to

extend any construct, if it is necessary. In our

approach, we define the semantic of control flow

constructs in Coloured Petri Nets (CPNs) (Jensen,

1997). Each control flow construct is modelled as a

Coloured Petri Net (CPN) model, namely a

workflow component. A component is constructed

according to the following modelling rules:

• The component is framed between an input place

and an output place,

• A place holds the unique identification code for

the component,

• Apart from the input and output places, a

component may have other places which are

local to the component,

• Components can be linked (chained) using their

input and output places.

A component may contain other components.

This characteristic allows modelling of a very

complex workflow. The modelling approach we

present in this paper is a high level representation of

577

Salimifard K. (2004).

COMPONENT-BASED MODELLING OF ORGANISATIONAL RESOURCES USING COLOURED PETRI NETS.

In Proceedings of the Sixth International Conference on Enterprise Information Systems, pages 577-580

DOI: 10.5220/0002652005770580

 SciTePress

control flow constructs. We introduce different

modelling components and their semantics using

CPNs. The CPN models have been designed using

Design/CPN software tool (Design/CPN Reference

Manual for X-Windows, 1993).

3 ORGANISATION MODELLING

The capability of thorough representation of

organisational resource has become an important

feature of workflow management systems. While

the researchers have mainly focused on structural

modelling of organisational resource, the dynamic

aspects such as resource efficiency and non-

operational behaviour of human resources have

captured less attention.

In our approach an organisation model is

composed of four parts which are modelled as CPN

pages. In general, an employee as a human being has

a very complex behaviour. We draw a model

representing the abstract behaviour of employees in

an organisation. The model is depicted in Figure 1.

Figure 1: Staffs’ abstract behaviour

Any available member of staff may have either

of three abstract class of behaviour at a time. Job

fetching refers to a situation where an employee is

dealing with the selecting (assigning) an available

work-item. A member of staff may be processing a

work-item, which he already has been assigned to.

This behaviour is represented by the Job processing

entity. Behaviours that are not productive have been

classified under the term Non-Operational

behaviour. The term implies that such behaviour is

not part of the employee’s organisational duties.

3.1 Player Query and Scheduling

Work Items

In a workflow system environment, an organisation

unit, e.g. Accounting department, processes those

workflow activities that require a service from that

organisation unit. An organisation unit offers its

services to the system through the exchange of

request for service (RfS). That is, the process level

submits a work item to the organisation unit as an

RfS. A work item is a representation of a workflow

activity modelled as a CPN binding element. It

carries information about processing requirements

such as department, role needed, and the estimated

processing time.

The generic model of the query part of the

organisation model is depicted in Fig. 2. The figure

is modified for the department with the code 1, as it

is appeared as D1 in Fig. 2. The place D1ID holds

the department identification code as the initial

marking.

Figure 2: CPN model of query part

Upon receiving an a msgt token through D1inp,

the transition D1inGate is enabled. Occurrence of

this transition consumes a token from D1inp and

creates a new token in D1Dis. The created token is

of color-The function NOWt() determines the arrival

time of the work item.

The place D1StaffAv holds all the staffs available

at the department. Based on the organisation policy,

the maximum number of jobs each staff is assigned

to is determined as the initial marking for D1Lmt.

The initial marking of D1StaffAv determines

Job

Fetching

Job

Processing

Non-Operational

Behavior

Staff

busy

released

assigned

assigning

off work

back work

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employees who are initially available. The role

classification for the department is defined as the

marking of D1Roles.

3.2 Work Item Assignment

All the work items have been accepted to be

processed by the department are kept in the

department in-tray, accessible by employees. A

work item in the in-tray can be fetched via the

occurrence of the transition D1Schedul. It has a four-

facet and complex behaviour described as follows:

• Role matching: upon the availability of a token

in D1Dis, it checks whether any role defined in

D1Roles matches with the reqRole parameter of

the work item.

• Staff availability if a player is found, the

availability of the player is checked.

• Quota checking: if the result of the previous

check is positive, it checks the number of jobs

currently the employee is assigned to, i.e. noj,

against the maximum number of jobs an

employee can be assigned to, i.e. [noj ≤ lmt].

• Job list updating: if the results of both previous

tests are positive, the job list associated with the

employee has to be updated.

The newly work item selected will be appended

at the end of the employee’s job list. The actual

processing time of the work item is determined

using the function TIM().

3.3 Processing Work Items

The processing of a work item is diagrammatically

represented in Fig. 3. The start of the execution of a

work item is modelled using the transition

D1JobStart. Its occurrence is explicitly conditioned

by the exact matching of the player whose job list is

available in D1SchEd and the employee available in

D1StaffAv.

A job list is in fact a simple queue from which

the owner selects the work items to process. The

selection can be done using different queue

disciplines (Kleinrock, 1975). In our approach, we

assume that the organisation committed to use the

FIFO discipline. The output arc between D1JobStart

and D1JobinPro (see Fig. 3) inscribed with the work

item and its “end_of_process” time, i.e. #Jpt job.

This arc also carries the information about the

employee who is processing the work item.

Figure 3: The job execution model

3.4 Releasing Resources

The sojourn time of the token in D1JobinPro

indicates the processing time of the corresponding

work item. The transition D1releas occurs and an

msgf token is sent to D1outp indicating that the work

item has been successfully processed. Additionally,

the employee who was performing the job is

released and the corresponding token is sent back to

D1StaffAv.

4 MODELLING NON-

PRODUCTIVE ASPECTS

The need to represent the behaviour of individual

employee as well as organisations has been

expanding as a result of the increasing use of

simulation and systems analysis. The generic model

of non-operational behaviour of human resources is

depicted in Fig. 4. Transitions D1off and D1back

model the off-work and back-to-work behaviour,

respectively. The time duration between two

successive off-works is a stochastic random variable.

The place D1NoE is a counter keeps the current

number of available employees.

The occurrence of D1off has three effects on the

rest of the model. Firstly, it takes a staff token from

D1StaffAv and decreases the counter value by one.

Secondly, it determines the next time that another

off-work happens. Thirdly, it specifies the duration

of the off-work period using the function offDur on

the output arc to D1Ret. For the employee who is

off-work his corresponding token is kept in D1Away

while D1Ret keeps the corresponding off-work

period. The occurrence of D1back takes the staff

token from D1Ret and sends the token back to

D1StaffAv.

COMPONENT-BASED MODELLING OF ORGANISATIONAL RESOURCES USING COLOURED PETRI NETS

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Figure 4: Model of non-operational behaviour

5 SUMMARY

In this paper, we have presented a component-based

resource model. This method incorporates both the

static and the dynamic issues of human resources.

Role-based classification as it is required by most of

leading workflow management systems, as well as

the individual efficiency of employees has been

taken into account. The behaviour of human

resources has been classified into fetching work

items, processing work items, and non-operational

behaviour. Each class of behaviour has been used to

derive an appropriate CPN representation.

Using the CPN as the modelling schema, allows the

separation between the process model and the

organisation model. This separation gives much

flexibility in modelling and modification.

Additionally, CPN-based modelling characterises

the proposed method with powerful expressiveness

and capable to be linked to the process model.

In this paper we mainly focused on the designing a

workflow process regardless of the performance of

the model. To finalise a workflow process model,

the performance of the model has to be studied. The

performance of a workflow model depends on the

WfMS and the management of resources. Therefore,

it is required to integrate a workflow process model

into organisational model, in order to study the

performance of the workflow process.

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