TASK MODEL REPRESENTATION OF A COLLABORATIVE

SYSTEM USING HYPERMEDIA NETWORKS

Beatriz Jiménez, Miguel Sánchez, Francisco L. Gutiérrez and Nuria Medina

Department of Computer Languages and Systems, University of Granada

Periodista Daniel Saucedo Aranda s/n, E-18071 Granada, Spain

Keywords: Task models, hypermedia networks, collaborative systems.

Abstract: This paper presents a method for representing the task models of collaborative systems using hypermedia

networks. The aim is to represent these models flexibly and extensibly so that they may be managed in web

environments. This approach considers three relevant aspects of collaborative systems: the organization’s

structure (roles), the tasks to be performed by organization members, and the resources necessary for

carrying out these tasks. The AMENITIES methodology will be used to represent the initial models which

describe these three aspects in collaborative systems. These initial models will be the basis for representing

the transformation process for achieving our hypermedia network.

1 INTRODUCTION

One important feature of current systems (Vernadat

1996) is the existence of collaborative processes

where different users communicate and cooperate in

order to achieve common aims. Unfortunately, when

we decide to specify a collaborative system we find

that the actor’s behavior and interaction to carry out

different tasks cannot be defined statically as a result

of the changing context of such systems. These

context changes have their effect on task

management, and while the development of a system

is complex, it is also necessary to pay special

attention to dynamic task management.

Our research group GEDES is currently working

on the development of a Web Service Architecture

(WSA) for collaborative systems (Gutiérrez et al.,

2006a), the main objective of which is to enable the

adaptation and evolution of system behavior and the

security and coordination of task management.

While task models allow us to pinpoint the problems

of such systems and to find solutions for them at a

conceptual level, they cannot be executed directly on

the proposed architecture and so another

representation is necessary. In this paper, we will

represent cooperative task models with hypermedia

networks to obtain a flexible, extensible and easy-to-

integrate representation with the different

architecture services at the execution level. Our idea

is to use hypermedia networks to control the

workflow generated between different data in our

system.

Section 2 of this paper presents an existing

approach for workflow collaboration. Section 3

describes a task model approach that makes up a

complete model for collaborative system

specification. Section 4 details our approach for

representing task models using hypermedia networks

with an example. Finally, Section 5 outlines our

conclusions and our future lines of research.

2 RELATED WORK

Web services are components which are based on

WSDL (W3C-WSDL), UDDI (OASIS-UDDI), and

SOAP (W3C-SOAP) industry standards, and enable

different organizations to be connected

independently of the platforms and languages used

in each one (Leymann, 2003). In recent years, many

workflow approaches have been developed and

these allow different processes in a system with

complementary skills to cooperate. These

approaches divide an application into two strictly

separate layers: the top layer (the business process)

which is written in the Business Process Execution

Language for Web Services (BPEL4WS or BPEL)

(Leymann & Roller, 2000) and represents the

application’s flow logic; and the bottom layer (the

web services) which represents the application’s

113

Jiménez B., Sánchez M., L. Gutiérrez F. and Medina N. (2007).

TASK MODEL REPRESENTATION OF A COLLABORATIVE SYSTEM USING HYPERMEDIA NETWORKS.

In Proceedings of the Third International Conference on Web Information Systems and Technologies - Society, e-Business and e-Government /

e-Learning, pages 113-120

DOI: 10.5220/0001271801130120

 SciTePress

function logic. This structure has several advantages

over more conventional approaches: firstly, both the

underlying business process and the invoked web

services can be changed with no impact on the other

web services within the application or on the web

services that the business process represents; and

secondly, the application can be developed and

tested in two separate stages: the business process is

developed and tested independently of the

development and testing of the individual web

services. As a result, it is therefore possible to easily

make changes to the application.

The advantages provided by web services have

been recognized by the UML community, and have

been taken advantage of for UML to BPEL mapping

and for the relations corresponding to Model-Driven

Architectures (MDA) (Gardner, 2003). None of

these web service standards and approaches,

however, provides support for the coordination of

activities where the sequence of activities to be

carried out is undefined - a typical situation in

collaborative systems. Correspondingly, our work

presents an approach to enable navigation within a

hypermedia structure by means of the flows of aims

and subaims which have not been pre-established, in

order to obtain effective coordination within

collaborative systems where the uncertainty

common to task models makes it impossible for a

pre-established sequence to be followed.

3 TASK MODELS

Task models are defined as logical descriptions of

the activities for obtaining the user’s aims and goals

and for showing how the user perceives the system

(Van der Veer & van Welie, 2000; Paterno, 2001).

Taking into account this definition and the need to

describe tasks in collaborative organizations, task

models are an ideal means of specifying what

information is used in task management and how

these tasks interrelate with each other.

Figure 1 shows a conceptual model diagram for

describing tasks in an organization. This model is

part of a complete model defined in the ADACO

research project for modeling collaborative systems

(Gutiérrez, 2006b). Tasks are classified into abstract,

individual, and team tasks. While abstract tasks are

tasks that gather other tasks, team tasks are one or

more tasks that are carried out by user groups

sharing common aims.

Both abstract tasks and team tasks eventually

consist of individual tasks. In team tasks, the

individual tasks will be performed by different team

members (always under the influence and dynamics

of teamwork) with a shared but not clearly assigned

responsibility. Individual tasks are considered to be

application tasks, interaction tasks, or user tasks .In

order to establish this classification we follow

Paternó’s CONCURTASKTREE approach (Paternó,

1999) for modeling collaborative tasks.

Figure 1: Task model.

By analyzing the conceptual model, we extract a

set of considerations to obtain a hypermedia

representation. Firstly, it is necessary to bear in mind

that the reason why a process is successful or not

will depend not only on its logic of application but

also whether the aims associated with each task have

been completed. Secondly, we must bear in mind the

relation between actors and tasks: a task is not

directly related with the actor, but the roles they

carry out show their responsibilities in the tasks to

be performed. There is therefore an indirect relation

between actors and tasks through the roles. Finally,

but just as important, another aspect in task

coordination in collaborative processes is the control

and presence of resources associated with actions in

a task. Protocol and session concepts, which are part

of the task model, will not be taken into account in

this work. In the following section, we will present

and provide examples of our approach for

representing task models using hypermedia

networks.

4 HYPERMEDIA

REPRESENTATION

The advantages of a hypermedia representation are

that information structuring, navigation facilities,

and simultaneous use of resources (for example)

allow us to organize task model information in an

extensible and flexible way so that these models can

be managed in the web environment. From the

observations presented in the previous section, in

order to carry out a hypermedia representation of

task models, it is necessary to consider and represent

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three relevant aspects: the organization’s structure

(roles), the tasks that must be performed by the

organization members, and the resources necessary

to carry out these tasks. For each aspect, we create a

particular hypermedia structure and by joining all

these structures together we obtain the global

hypermedia network which represents the

collaborative system.

In order to make the representation process more

comprehensible, all the steps will be illustrated by

studying a particular example which illustrates the

web version of the board game Pictionary. The

game is carried out as a collaborative task with

different users taking part and playing different

roles. In the game Pictionary, a user can either play

or watch other users play. It is necessary for users to

not if they want to watch one.

A game will begin when there are at least four

registered users, divided into two or more teams of

two or more players. The player whose turn it is

throws the die, moves a counter and picks a card

from the pack. The drawing phase then begins and

players must then draw pictures for their team mates

(in the case of a “TeamPlay” card) or all the players

(in the case of an “AllPlay” card) to guess the word.

This stage finishes when a player guesses the picture

or the timer rings, and it is then another player’s

turn. The game continues until one team reaches the

finish and the team with the highest score wins. A

moderator watches the game throughout to ensure

that the rules are followed correctly.

The following sections 4.1, 4.2 and 4.3 will

describe the representation of the organization’s

structure, the tasks, and the resources. In the three

cases, AMENITIES (Garrido, 2003), a structured

method for cooperative models, is used to represent

the initial models that describe the system.

4.1 Representation of the

Organization’s Structure

The first step in our hypermedia representation is to

analyze the actor’s behavior in the system: role

specification and role change in the organization.

Figure 2 shows the organization of the system by

means of an Organization Diagram used by

AMENITIES to describe organizations using a

special type of UML state diagram, where roles in

the organization are treated as states and role

changes as changes of state. The system that we

want to represent is structured as a general

organization (which we call Pictionary) and a more

specific suborganization (which we call Team).

In the Pictionary organization, we can identify

four roles: Moderator, URegister, UGuest, and

Observer. The rhombus joined to the initial state

(black dot) shows the initial possibility of acquiring

two different capacities. Any actor acquiring the

capacity guest? can carry out the UGuest role, but if

an actor acquires the capacity authorized?, they will

carry out the URegister role. The remaining roles

performed by an actor will depend on the capacities

acquired as the game evolves.

Actors carrying out the initial role URegister

could change to the Moderator role if they decide to

moderate a game (moderate? capacity), or to the

Observer role if they decide to observe a game but

not to play (observer? capacity), or to the Player

role in the Team organization if they decide to play a

game (play? capacity). Actors carrying out the

UGuest initial role could only change to the

URegister role when they acquire registered?

capacity. The cardinality 2..NMax in the Team

flowchart indicates that a game begins when there

are at least four registered users, divided into two or

Figure 2: Organization Diagram for Pictionary and Team.

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Figure 3: Hypermedia network for organization Pictionary and Team.

more teams of two or more players. Actors with the

Player role could then change to the PTurn role after

they acquire the turn? capacity. This role allows the

actor to throw the dice, pick a card and draw a

picture. The remaining actors with the Player role

will change to the PActive role if they acquire the

response? capacity to guess a picture.

In order to represent the flowchart information

by means of a hypermedia structure, an ontological

representation of roles and transitions is necessary to

represent role changes. Consequently, two types of

nodes are defined in our hypermedia representation:

nodes to represent roles, and nodes to represent

capacities and/or laws that produce role changes.

There are also two types of transitions between

the states in the flowchart: non-additive transitions

(original role is left and cannot be recovered later)

which are represented by a single arrow in Figure 2;

and additive transitions (original role is recovered

later) which are represented by a double arrow in

Figure 2. In order to represent this information in

our hypermedia structure, in the case of non-additive

transitions, there is a single link from the node

representing the origin role to the node representing

the destiny role. In the case of additive transitions,

however, it is necessary for there to be two links in

opposite directions between the origin and destiny

roles with two intermediate nodes to represent the

changes to acquire the destiny role (see node

AModerate in Figure 3); and the changes to recover

the origin role and leave the destiny role (see node

LModerate in Figure 3). For organizations with no

single initial state (in the example there are two

different access modes URegister or UGuest

depending on the capacity that has been acquired),

we must include an additional node (see UPictionary

in Figure 3) to represent these initial role changes.

This initial node is represented by a double ellipse

node.

Figure 3 shows the complete hypermedia graph

for the flowchart in Figure 2. The hypermedia model

obtained allows us to navigate through the possible

role sequence in the system. At execution time, it

can be used to control the user’s authorization to

change from a certain role to another.

4.2 Task Representation

The second step in our hypermedia representation is

to analyze task management in the system: tasks

carried out by a role, concurrent tasks, event

triggering, etc. In AMENITIES, the Role Diagram is

the connection between the organizational structure

and the tasks to be carried out by members in the

organization. Figure 4 shows the association

between tasks and roles for the specific role JTurn.

Figure 4: Role Diagram JTurn.

This role can carry out two tasks: a collaborative

task, Play, which we will describe later, and an

individual task, LeaveGame. The cooperative task

Play can be interrupted by the task LeaveGame at

any time. The cardinality of the cooperative task

Play establishes that a minimum of four players are

needed for a game to start. The representation of this

diagram produces a new graph (level Role-Task in

Figure 5) that will be the connection between the

organizational hypermedia graph (level Roles in

Figure 5) and the tasks to be carried out by members

in the organization (level Tasks in Figure 5). Each

task is represented by a node on the hypermedia

graph. A link can represent two different concepts:

execution or interruption. More specifically, there

will be a link from each task node to the role node

that executes it; there will also be a link from each

interrupted task node to the task node or nodes

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which interrupted it (see Play and LeaveGame nodes

on the Role-Task level in Figure 5.

The next step will be to complete the

hierarchical task level by considering the detailed

specification of the execution of each task. Figure 6

shows the AMENITIES specification for the

cooperative task Play by means of a Task Diagram

and the subactivity TurnGame (which belongs to the

task Play) by means of a Subactivity Diagram.

AMENITIES uses the Task Diagram to describe the

action sequences for an activity. The cooperative

task Play comprises two actions (BeginPlay and

FinalizePlay) and one subactivity (TurnGame),

which is represented by two states joined by a

transaction in the bottom left-hand corner.

AMENITIES uses the subactivty term to define

work units composed by a set of actions and other

subactivities to structure tasks, The action term to

describe an atomic work unit. The times no-winner

clause shows us that TurnGame will be instantiated

while winner is not found. The subactivity

TurnGame is defined with two main concurrent

constructions (between solid lines).

The execution of the first set of

actions/subactivities ThrowDice, MoveCardGame,

PopCard, ThrowCrono DrawCard and

ResponserCard finish when all the

actions/subactivities have finished (transition with

no event), and the subactivity ModerateTurnGame

finishes when the event FinalizeTurnGame occurs.

The subactivity ThrowDice is executed by the role

PTurn. The subactivities MoveCardGame and

PopCard will be executed by the system. After

PopCard we can obtain two possibilities: if an

“AllPlay” card is picked, the event AllPlay is

triggered; if a “TeamPlay” card is picked, the event

TeamPlay is triggered. The rest of the sequence is

defined with a new concurrent construction: the

subactivity DrawCard which is executed by the role

PTurn and the subactivity ResponseCard which is

executed by the role

PActive. Both subactivities

finish when all their actions/subactivities have

finished (transition with no event) or when the

CronoZero event is triggered.

In order to represent the information shown in a

Task Dagram by means of a hypermedia graph, an

ontological representation of actions/ subactivities

and the transitions between them is necessary. In this

case, we consider three types of nodes: nodes which

represent actions/subactivities; nodes which

represent sending of signs and events; and nodes

which represent the global aim associated with a

task.

Figure 5: Hypermedia network for the role-task connection PlayerTurn-Play and for the task-subactivity connection

Play-TurnGame.

TASK MODEL REPRESENTATION OF A COLLABORATIVE SYSTEM USING HYPERMEDIA NETWORKS

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Figure 6: Task Diagram Play and Subactivity Diagram TurnGame.

In the previous sections, we have mentioned that

the success of a process will depend not only on its

logic of application but also on whether the aims

associated with each task have been completed.

There might be situations where rather than a task

being executed on the basis of a formal execution of

the tasks comprising its workflow, achievement of

the aims and subaims associated with the tasks will

be sufficient. Such a situation is typical in

collaborative processes where the sequence of

actions to be carried out by actors is not clear but the

desired aim is.

The links in the hypermedia structure represent

the flow between the subactivities of each task

taking into account the different laws of application:

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 The sequential execution of instances

of a same activity is represented by means of a

cyclical link from/to the node representing the

subactivity (see the node TurnGame in Figure

5).

 Initial subactivities in a concurrent

flow are represented by means of an arc which

joins their respective links with the previous

subactivity prior to the concurrent section.

 We therefore indicate that it is

necessary to visit all the concepts, i.e. all the

concurrent subactivities must be executed (see

the node BeginTurn in Figure 5).

 For conditional flows, the initial

subactivity is the subactivity prior to the

condition in the diagram, and the destination

subactivities are each possible subactivity

after the evaluation of the condition (see the

node PopCard (origin), and AllPlay and

TeamPlay (destinations)). We use a dashed arc

to join the links from the possible origin

concept to the destination concept in order to

indicate that this concept can be reached from

any link, i.e. only an origin subactivity must

be executed (see the nodes ThrowCrono and

WriteScore).

The shaded nodes on the Task and Task-

Subactivity level represent the aims associated to a

task (see the concept SolvedGame in Figure 5). The

navigational links between activity nodes and aim

nodes allow us to coordinate activities where the

sequence of activities is not clear, and we can

navigate through the sequence of activities or the

aims. This double path allows a more effective

coordination in collaborative systems where

uncertainty in task models is an important aspect.

The initial nodes for each level are represented by a

double ellipse and the links between the nodes at

different levels are represented with dashed lines.

If a task has more than one initial subactivity (in

the example, the subactivity TurnGame is initiated

with a concurrent section comprising two

subactivities), we must include an extra node (in the

example, the node BeginTurn) for play to start.

4.3 Resource Representation

The third step in our hypermedia representation is to

analyze the use of resources in the system. Next to

the task description it is possible to perform a

parallel description about the objects used by the

different tasks under different roles. In

AMENITIES, these objects can be of two types:

artifacts, i.e. technological units which support the

carrying out of certain collaborative actions - for

example the drawing board (see Resources:Board in

Figure 6); and information objects, i.e. entities with

information for carrying out certain actions - for

example to register the score (see

State:UpdatePunctuation in Figure 5). Both

concepts appear in the Activity Diagram that

describes the tasks and are represented using UML

class diagrams.

In Figure 6 we can see how the subactivity

ThrowDice uses the resource Dice in the cooperative

task Play. The subactivity DrawCard uses the

resource Board, and ResponseCard and

ModerateTurnGame use the resource Chat

concurrently. For hypermedia resource

representation, it is necessary to include on the

task/subactivity level a node for each resource and a

link to represent the use of that resource by a task.

The hypermedia graph on the Task-Subactivity level

is shown in Figure 7. The shaded nodes represent

resources nodes.

Figure 7: Hypermedia network task TurnGame.

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5 CONCLUSIONS

In this paper we have presented an approach to

represent task models using hypermedia networks.

More specifically, we have constructed a

hypermedia structure for each of the three

fundamental aspects in a collaborative system: the

organization’s structure (roles), the tasks, and the

workflow in each task (subactivities). We have also

considered and integrated in these structures two

equally important elements: the resources needed to

perform the tasks, and the aims and subaims that

indicate whether the tasks have been satisfactorily

completed in situations where task execution cannot

be handled with the simple formal execution of their

workflow.

The combination of the structures obtained as a

result of this process represents a single global graph

which enables us to obtain a dynamic specification

that is capable of adapting to changes in context, and

thanks to this, we are able to reflect changes in the

actors’ behavior. It is not necessary therefore for the

workflows to be pre-established, but rather the path

to be followed at any given time will be determined

by the achievement of the aims (conditioned by

changes in context).

Our future work will concentrate on the

inclusion of the hypermedia network obtained in our

web service architecture for the implementation of

collaborative systems. Within this architecture, we

propose a web service to coordinate workflows

which appear in the different existing applications.

The hypermedia network obtained will become the

information centre which the web service needs in

order to carry out all its activities in a flexible way.

Other studies will be focused to analyse the

integration of this representation into existing

approach such as UML activity diagrams or BPEL

specifications.

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