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A Scaleable Heterogeneous Architecture for Agent – Oriented Workflow
Management
Content Areas: Agent Technology, Interoperable Agent Platforms, FIPA, Workflow Ma nagement
John Hickie 1, James Kennedy1, Georgios Koudouridis 2, Vaggelis Ouzounis 3 and Matthew Studley 4
1 Broadcom
Éireann Research Ltd.,
Kestrel House, Clanwilliam Place,
Dublin, Ireland.
[email protected]
[email protected]
2Telia
Research AB
Vitsandsgatan 9, D713,
SE- 123 6 Farsta, Sweden
[email protected]
3GMD
- FOKUS
Vaggelis Ouzounis
Kaiserin-Augusta Allee 31
D-10589 Berlin, Germany
[email protected]
4
BT Laboratories
Martlesham Heath, Ipswich IP5 3RE
United Kingdom
[email protected]
“This paper has not already been accepted by and is not currently under review for a journal or another conference, nor will it
be submitted for such during IJCAI's review period.”
interoperability and scalability in these tools has
been identified as a serious weakness. P815
proposes a workflow architecture that will
address these issues by applying agent standards
and technologies. This agent architecture is
found to map well to the problems described
above.
Abstract
With a growth rate of 35% per annum, the workflow management market has become a multibillion dollar business. This paper describes the
work of the EURESCOM P815 project, which is
investigating the advantages of bringing agent
concepts and technologies to this booming sector. Existing workflow systems provide an intuitive way of defining and controlling business
processes. However, a lack of
1
Introduction
This paper discusses the ongoing work in the EURESCOM
project P815. This project concentrates on applying agent
technologies and standards to the management of business
processes. However, this paper focuses on one of the casestudies under development and in particular how this casestudy achieves a scalable interoperable architecture for
agent-oriented workflow. Section 2 outlines traditional
workflow and identifies various shortcomings, while section
3 outlines the case-study under consideration.
2
Traditional Workflow Management
Workflow systems have evolved over time to meet the demands of current business processes. A workflow management system (WfMS) will make sure that individual tasks in
a process will occur in the order in which they are supposed
to. A number of different software packages have been developed to perform this task. The WfMS traditionally developed have been proprietary. Different systems will have
different approaches, strengths and weaknesses, consequently there is a lack of interoperability between them. To address this problem, the Workflow Management Coalition
has been set up to try to integrate offerings from different
vendors. Although much of this specification is complete, it
is not widely adopted. However, the specification provides
an insight into the commonalties between vendors. The
workflow
reference
model
(http://www.aiim.org/wfmc/mainframe.htm) attempts to depict the general structure of workflow systems. These systems are based upon the precept that the workflow relevant
and non-workflow relevant data should be separated. This
data is separated by maintaining two information sources,
one for each of the above. The workflow engine instructs
tasks to start based on the information held in the workflow
relevant database. The task then starts, knowing where to get
its data from the non-workflow relevant database. This model works well for centralised systems, where database access
is ubiquitous. However, in distributed systems, there is no
such central repositories as central databases start to become
performance bottlenecks as the scale of the workflow system
increases.
Aside from this model of communication, there are other
important aspects of workflow management system design.
Chief among these is how the user is allowed to define
their business logic, and how that business logic maps
onto the underlying operational data.
2.1
Business Logic and Data
In any WfMS, two types of data flow can be clearly distinguished; the data flowing between the entities which
perform tasks (the actors), and the data associated with
the initiation and control of these entities’ activities. The
first, referred to by the Workflow Management Coalition
(WMC) as ‘application data’, may be defined thus;
‘Data which is application specific and not accessible by
the WfMS’ reference model [WfMCa].
The second, the business logic or ‘workflow relevant
data’, is defined by the WMC as;
‘Data that is used by a WfMS to determine the state
transitions of a workflow instance, for example within
pre- and post-conditions, transition conditions or workflow participant assignment.’[WfMCb].
There is a clear advantage in maintaining a partition between these data types. The workflow relevant data has
nothing to do with the underlying tasks. While the actors
may change, a given process may remain the same; all
that is required is that there exists an actor for each role
referred to within the process definition. Equally, an
actor may be required to enact his role as part of many
different processes, and in many instances of these processes.
2.2
Shortcomings of Traditional Workf low
The rapidly increasing capability and flexibility of telecommunications technology, especially the emergence and expansion of the WWW, Internet/Intranet and broadband network infrastructures, have brought a number of new possibilities and challenges to the design and organisation of
business activities using telecommunications networks. Such
possibilities and challenges determine the changes in the
features or emphasis of business process management.
The ubiquity of business processes and activities in the
emerging global information infrastructure (GII) requires a
WFMS to offer the following features:
 Openness
A business context in the emerging telecommunications
environment accommodates a variety of heterogeneous
roles, players and software/hardware components/tools.
All these can not be fully identified at the WFMS development phase. A suitable WFMS design should therefore
support a higher degree of openness with the twofold
meanings:
 open to the integration of (and the interoperation with) highly heterogeneous software components and tools that could exist in the global
environment in which the WFMS is to be deployed,
 open to the accommodation and integration
of/interoperation with heterogeneous business
sub-contexts with their specific requirements,
roles and players.
 Dynamic Nature
Business processes within the virtual telecom world will
have a highly dynamic nature in relation to the environmental business restrictions, customer requirements, internal objectives/interests and the technologies deployed
by the local organisations or the partners. Each process
has to therefore dynamically modify its model and
knowledge of the business contexts, and adapt its functions following the evolution of the business requirements. As a result, a WFMS should enable the business
processes/activities to dynamically/reactively adapt
(learn) their co-operation interfaces (services, APIs) and
behaviours, especially by negotiating and interacting
with their environments.
 Distribution and Globalisation
Globalisation of the telecommunications infrastructure
enables the wide distribution of business activities within
the workflow instances. Unlike traditional WFMS scenarios, where workflows are typically managed within
relatively small administrative and geographical domains, future WFMS will have to deal with concurrent
business processes that are distributed over large areas
such as countries, and over physically different enterprises (e.g. federation for Virtual Business Enterprises).
 Decentralised, Autonomous Activities
Emerging virtual business applications typically consist
of decentralised and autonomous entities. One example
is the Virtual Business Enterprises, where independent
enterprises can jointly form a federated new business for
specific interests and for a specific duration. Each business entity/process in this context can have its own objective and agenda, and will base its behaviour on the
feedback from the environment. Co-operations and coordinations will have to be based on dynamic negotiations following either pre-specified or dynamically negotiated protocols.
2.3
Agent-Oriented Workf low
Current WFMSs, based on the traditional Remote Procedure Call (RPC) paradigm, support only the very basic
services for workflow modelling, enactment and coordination. Most of these services are in the context of
workflow process/activity life-cycle management. The
idea behind agent-oriented workflow management system
(AoWfMS) is to utilise the agent-oriented paradigm to
augment and enhance WFMS systems to manage business processes enacted in highly dynamic and distributed
environments. Specifically, agent-oriented workflow
contributes to the WFMS system’s objective to achieve
high availability and reliability of management activities.
In contrast centralised WFMS schemes result in bottlenecks around the WFMS servers, while AoWFMS
achieve flexibility by distributing control. AoWFMS
provide mechanisms for co-ordination among workflow
activities and processes that are fault and exception tolerant, and dynamically distribute service functionality to
achieve a load balance among service processing management sites. Agent systems are traditionally well suited
to solving this type of problem. This will be better understood in the sections that follow. So far, there is no
universally accepted definition that clarifies the exact
semantics of the notion agent. Rather than attempting to
define an agent it is better to identify and reason upon
some of the properties of agents and their contribution to
WFMS systems.
According to the definition given in [Wooldridge] 1, an
agent is a problem solving entity that has the following
properties:
Autonomy: An agent is autonomous in the sense that it
does not require direct intervention from the user to carry out its tasks. It has control over its actions and internal
state.
Pro-activity: An agent dynamically pursues its goals that
have either been assigned by the user or activated due to
external events. Being pro-active means being goaloriented.
Reactivity: As agents have the ability to perceive their
environment, they can react appropriately and in a timely
fashion to changes in it.
Social ability: An agent can interact with other agents
and its user by means of communication based on
speech-acts. This communication provides a means for
agents to co-ordinate their actions and to co-operate with
other agents.
AOWfMS address the above-mentioned shortcomings of
WfMS in the following ways.
Openness – the integration between heterogeneous system becomes easier because agents provide a speech-actbased communication allowing the agents to be loosely
coupled.
Dynamic Nature – coping with changes and exceptions
as they arise could be possible due to the agents’ ability
to perceive their environment and co-ordinate themselves
and their actions accordingly during run-time.
Decentralisation & Autonomy – rather than having centrally imposed control agents can, by being autonomous
and goal-oriented, evaluate and decide upon their own
actions based on their own goals and the prevailing circumstances
1
Defining an agent has been the subject of a lot of debate in
the agent community. The literature abounds with attempts
to define agency, with attempts varying from rigorous to
informal (see [Franklin], [Petrie 96], [Russell & Norvig 95]
and [Wooldridge] for example). The definition of an agent
put forward by Wooldridge and Jennings, however, seems to
have gained widespread acceptance.
Distribution & Globalisation: - distribution of system
elements is also an inherent characteristic of an
AoWfMS due to the delegation and co-ordination of actions between agents that could be situated at different
locations.
In the rest of this paper and in terms of workflow, we
focus on the “openness” issue, as this is the main objective of our proposed scalable heterogeneous architecture
for AoWfMs .
3
P815 AoWFMS : A Case-Study in
International Leased Line Provisioning
3.1
Business Process Def initions
The process definition as defined by WfMC [WfMCa] is
the computerized representation of the activities, steps,
participants, rules and sequences involved in a particular
process. It depicts, for example, process initiation and
completion conditions, rules for driving process activities, user tasks to be undertaken, references to applications which may be invoked and definition of any required workflow relevant data. The process definition
can be represented in textual and/or graphical form or by
means of a formal language notation, which can be the
same as the content language used for representing an
agent’s knowledge. In either case, a process definition
language should be equipped with semantics required for
the description of business processes and should also
allow goal-oriented specifications of activities (that is, a
description of what is to be achieved rather than prescribing how it is to be achieved).
Figure 1 illustrates the main structural elements of a
business process.
Begin business process definition
Parameter value
(business process
:name ”Inland Section Provision”
:type composite
:role ”Inland Section Representative”
:data (in (SLA-ID #4))
:pre-condition (order handled)
:post-condition (inland section provided)
:nodes
(process-node ”Inland Section Design”)
(process-node ”Inland Section Test”)
...
)
A business process definition is an object data structure
consisting of a sequence of process parameters, introduced by parameter keywords (constants) beginning with
a colon. As depicted in the figure and according to the
above discussion the process’s parameters state the following information:
process’s name (e.g. :name); process’s type (e.g. :type);
which composite or atomic initiation conditions for the
process to be enacted (e.g. :pre-conditions); termination
conditions indicating process termination (e.g. :postconditions); the role of the organizational entity (:role);
the process’s input and output application data (e.g.
:data); activities to be carried out within the process (e.g.
:nodes).
In the case where a process is atomic the parameter
“:nodes” includes the name of the function to be executed. As in the business process pre- and post-conditions
could also be atomic or composite, i.e., consisting of orbranches or and-branches of conditions. Conditions can
also be negative statements by using “not”. Depending
on the workflow engine, the data parameter can be used
to pass application data or references in the case where
control and data flow are separated.
The minimal functionality required for handling business
process definitions should include:
Editorial or graphical capabilities that facilitate the
definition of processes and enables designers to control process deployment. These capabilities can be either incorporated or external to the agent.
The maintenance of a repository used to store these
definitions.
A mechanism that deploys and distributes these definitions among agents and inserts these definitions in the
agents
These functions should be available both off-line and at
run-time to allow automatic and dynamic adaptations to
environmental changes.
3.2
Workf low Engine
The workflow engine must respond to an initiation signal
which indicates the type of process which is to be enacted. Using this information, the workflow engine retrieves a Business Process Definition (BPD) from a local
repository, and thence creates a Business Process Instance (BPI). There can be many BPIs concurrently executing, and these may be instances of multiple BPDs.
Business process parameters
Parameter expression
Figure 1: Main structural elements of a business process
A BPI may be thought of as a directed graph. Each node
in the graph may be a reference to a further BPD, similarly available from the local repository. Alternatively, a
node may define an activity in the BPI. Activities are to
be enacted by agents, which are long-lived entities who
register their abilities with a central directory. The
workflow engine uses the directory facility (DF) to find
the logical address of an agent which can satisfy the requirements specified by a non-BPD node in a BPI.
When an agent finishes its task, it signals the termination
conditions to the workflow engine. The workflow engine
may use these signals to make decisions on which step in
the BPI is the next to be performed.
In our case, there are three general types of agents that
support the execution and management of the business
processes.



Workflow Request Agent (WRA) - gets the requests for
business process execution/instantiation.
Workflow Engine Agent (WEA) - executes and monitors the execution of a unique BDI.
Resource Agent (RA) - provides the functionality required by different activities (non-BPD node in the
BPI).
In general, a client requests the execution of a business
process by sending a request for a BP invocation to the
WRA. In the sequel, the WRA instantiates a WEA. The
WEA will undertake the responsibility for the execution
and control of the BPI. Whenever an activity needs to be
executed the WEA locates the appropriate RA and ask it
to provide the required functionality. Whenever a sub-BP
needs to be executed the WEA contacts another WEA
and asks it to execute the sub-BP.
In general, a client can start a business process, pause a
business process, resume a business process and terminate a business process. Upon request of these operations, the WRA instatiates a WEA that will undertake the
responsibility to execute the BP. For that reason, the
WEA contacts the Business Process Repository, retrieves
the BPD and creates a BPI. After the creation of the
BDI, the execution of the BPI can be started. Whenever
a client wants to pause a BP, sends a requests to the
WRA and then the WRA pauses the execution of WEA.
Thus, the operations that the WEA will provide to the
WRA are the instantiation of a BPD, the initiation of a
BDI, the pausing of a BDI, the resumption of a BDI and
finally, the termination of a BDI. The WRA has full control over the execution of the BDI and, based on client
requests, can force the WEA to behave accordingly.
If the WEA identifies that the execution of the BDI
should be continued with the invocation of an activity,
then the WEA contacts the DF and locates the physical
address of the RA that can provide the activity. Then, the
WEA can request to start the activity, to stop the activity,
to terminate the activity or to resume the activity. When
the RA terminates, normally the provision of the activity
notifies the WEA by sending him a notification message.
The message can be sent either in synchronous or asyn-
chronous mode. Based on these messages the WEA can
evaluate the constraints of the BDI and decide the activity or sub-BP needs to be executed next.
If the WEA identifies that the execution of the BDI
should be continued with the invocation of a sub-BP,
then the WEA contacts the DF and locates the physical
address of the WEA that can support the execution of
this sub-BP. In the sequel, the source WEA contacts the
target WEA and asks it to instantiate the sub-BP. The
target WEA retrieves the sub-BP from the Business Process Repository, interprets it and creates a sub-BDI.
Based on this BDI, the target WEA will start the execution of the sub-BP. The source WEA can request it to
start the execution, to stop the execution, to resume the
execution and to terminate the execution. In any case, the
target WEA informs the source WEA about the results of
the sub-BPs by sending notification messages.
The above mentioned agents are interacting together in
order to support the execution of the workflow on behalf
of the clients by exchanging ACL messages. Three types
of messages can be exchanged, namely:



request messages
response messages
notification messages
Request messages are exchanged between an agent a and
an agent b when agent a wants a service or operation to
be executed by agent b. Response messages are exchanged when an agent b wants to respond to the request
message of agent a by providing the result of the operation requested. Finally, notification messages are exchanged when an agent b wants to inform an agent a
about the termination (normal or abnormal) of its task.
Messages can be sent either synchronously or asynchronously according to the needs of the agents.
In some cases, workflow occurs across the boundary of
organisational units. An example of this is the current
case-study, International Leased Line (ILL) Provisioning. Consider for a moment the following scenario:
There are two telecommunications companies, a and b.
A customer requests a to establish an ILL between two
points, a 1 and b 1, where a 1 is locally accessible to a and
b 1 is locally accessible to b. In such a case it is merely
necessary that a should know that there exists a BPD
within the remote domain b which can satisfy a’s requirements, subject to prior agreement. For the workflow engine, requests are received, and actors are discovered who can satisfy the task requirements. One
BPI’s actor may in some cases be another workflow engine, and a BPI’s initiating ‘customer’ may, vice versa,
be a remote workflow engine.
In this manner, the AoWfMS presented in this paper addresses the problems of scaling and encompasses hetero-
geneity. Different domains may be expected to have
BPDs that differ though they are functionally equivalent.
However, in so far as these BPDs can be referred to at a
level of abstraction that hides their differences, the heterogeneity between domains becomes transparent.
3.3
The P815 AoWfMS will use a FIPA [FIPA98] compliant
interface to communicate between heterogeneous WfMS.
In this way, FIPA agent message formats, can be used to
limit the amount of communications management needed. Table 1 depicts how issues such as session handling,
control of the workflow process and non-workflow relevant data are separated.
Agent Communication
Non-Workflow Relevant Data
An AoWfMS will need to communicate workflow relevant and non-workflow relevant data between its agents.
The workflow relevant data will be generic to all workflows that are modelled.
An example of this may be a ‘Start Task’ message that is
sent between tasks in a workflow. Equally, we might
expect a ‘Task Completed’ response from a task, which
has finished a requested service. These types of generic
messages have been well defined in the WfMC interoperability specification [WfMCa]. This specification outlines the type of messaging that might be expected in the
generic case. There are basic message types defined
which allow two workflow engines to communicate. Issues such as session and message handling are addressed
in [WfMCa]. The scale of what this specification attempts to do is perhaps reflected in the fact that the
standard remains largely unimplemented. Defining the
interfaces between different WfMS has lead to a lengthy
specification.
Agent communication technologies would seem to be
ideally suited to removing much of the complexity of
interoperability. Agent platforms may be used to ‘hide’
much of the detail, providing a layer of workflow management primitives upon which workflow systems may
communicate.
Agent standards for interoperability
[FIPA98] have grown in maturity over the last few years
to a stage where real applications may be built upon them
[FACTS]. There has already been work done on the application of agents for workflow interoperability [KAM].
The P815 project will focus on scalability and openness.
To improve the scalability of a WfMS, the handling of
workflow relevant and non-workflow relevant data is
key. In a centralised model, control of the workflow
process is separated from the data needed to complete a
domain specific task. This may be both a logical and
physical separation, as workflow specific data (control
data for the purposes of the workflow) is stored in a separate database. This approach helps to distinguish between the workflow process and the individual tasks.
However, in a distributed system, there may not be universal access to either workflow specific or nonworkflow specific data. Messages passed between systems will contain workflow specific and non-workflow
specific data. It might seem that this approach may blur
the lines between the two. To separate the two, much of
the communication management that was previously
specified in the WfMC interoperability specification,
will be replaced by agent communication tools.
Workflow Relevant Data
Agent Communication
(FIPA)
and
Management
Table 1: Three layers of communication in P815
AOWfMS
There is a distinct logical separation of workflow/nonworkflow relevant data. The workflow relevant data is
dealt with in the middle layer of Table 1.
4
Conclusions
Workflow Management would benefit from applying
agent-oriented technology in several ways. It is envisaged that an AoWfMS can obtain the required properties
of openness, dynamic nature, distribution and decentralisation by employing common agent features and capabilities as well as patterns for agent interaction. In this
paper we presented an architecture for an AoWfMS that
addresses the problems of scaling and encompasses heterogeneity to deal with the openness issue. By equipping
agents with a workflow engine and by utilising agents’
social ability and the way they communicate using
speech acts, we can achieve a WfMS that facilitates the
enactment of business processes in heterogeneous domains or even environments. Furthermore, as business
process definitions can be referred to at a level of abstraction that hides their differences, the heterogeneity
between domains becomes transparent. Additionally, the
proposed architecture enables the creation of an agentoriented workflow management system that is easily extensible in functionality and can adapt to changing business environments. Such a feature gives us a system that
can be deployed and developed at the same time . At the
time of writing phase 1 of the project, which builds the initial infrastructure, is under implementation. This phase concentrates on achieving interoperability between various
FIPA platforms with in-build workflow engines. Once this
phase is completed phase2 will build on this infrastructure to
determine the benefits of an AoWFMs. P815 is due for
completion in March 2000.
Disclaimer
This document is based on results achieved in a
EURESCOM Project. It is not a document approved by
EURESCOM, and may not reflect the technical position of
all the EURESCOM Shareholders. The contents and the
specifications given in this document may be subject to further changes without prior notification. Neither the Project
participants nor EURESCOM warrant that the information
contained in the report is capable of use, or that use of the
information is free from risk, and accept neither liability for
loss or damage suffered by any person using this information
nor for any damage which may be caused by the modification of a specification. This document contains material
which is the copyright of some EURESCOM Project Participants and may not be reproduced or copied without permission. The commercial use of any information contained in
this document may require a license from the proprietor of
that information.
References
[FACTS]
[FIPA98]
[Franklin]
http://www.labs.bt.com/profsoc/facts/
http://www.fipa.org/spec/FIPA98.html
http://www.msci.memphis.edu /~franklin/
AgentProg.html
[KAM]
Mohan Kamath, Oracle Corp., Krithi
Ramamritham, Pragmatic Issues in Coordination Execution and Failure Handling of Workflows in Distributed Workflow Control Architectures,.
[Petrie 96] Petrie, Charles J., ‘Agent-Based Engineering
the Web and Intelligence’, IEEE Expert, December 1996,
also
http://cdr.stanford.edu/NextLink/Expert.html
[Russell] Russell, Stuart J., Norvig, Peter. Artificial Intelligence: A Modern Approach. Englewood
Cliffs, NJ: Prentice Hall, 1995.
[WfMCa] Interoperability Abstract Specification, 20 th
October 1996, Workflow Management Coalition.
[WFMCb] Workflow Management Coalition: Terminology
& Glossary (WFMC-TC-1011, June-1996, 2.0)
[Wooldridge] Wooldridge, M., Jennings, N. Intelligent
Agents: Theory and Practice. The Knowledge
Engineering Review 10(2). pp.115-152. 1995.
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