ADEPT Workflow Management System:
Flexible Support for Enterprise-Wide Business Processes
–Tool Presentation –
Manfred Reichert, Stefanie Rinderle, and Peter Dadam
University of Ulm, Faculty of Computer Science,
Dept. Databases and Information Systems
{reichert, rinderle, dadam}@informatik.uni-ulm.de
Abstract. In this tool presentation we give an overview of the ADEPT
workflow management system (WfMS), which is one of the few avail-
able research prototypes dealing with enterprise-wide, adaptive work-
flow (WF) management. ADEPT offers sophisticated modeling concepts
and advanced features, like temporal constraint management, ad-hoc WF
changes, WF schema evolution, synchronization of inter-workflow depen-
dencies, and scalability. We sketch these features and describe how they
have been realized within ADEPT. In addition, we show which tools and
interfaces are offered to developers and users in this context. ADEPT
follows a holistic approach, i.e., the described concepts have not been
implemented in an isolated fashion only, but are treated in conjunction
with each other by integrating them within one WfMS.
1 Introduction
Long regarded as technology for the automation of well-structured business pro-
cesses, WF management is in the throes of transformation as more and more
non-traditional applications require comprehensive process support. In many
domains, like hospitals, engineering environments, or e-business, however, high
requirements with respect to functionality, flexibility, and scalability exist [1,2,
3]. In the ADEPT project, we have addressed these requirements from the very
beginning. In the meantime, we have developed an adaptive WfMS prototype,
which allows users to realize flexible, enterprise-wide WF applications.
In this paper, we give an overview of the ADEPT WfMS and its related
concepts, tools, and user as well as programming interfaces. Section 2 summarizes
basic features of the ADEPT WfMS, which have been described in more detail
in previous publications of our group [2,4,5]. In Section 3 we show how these
features have been realized within the ADEPT WfMS. Section 4 sketches selected
projects to demonstrate the usefulness of the developed WfMS. We conclude with
a short summary in Section 5.
This work was partially performed within the research project ”Change management
in adaptive workflow systems”, which has been founded by the German Research
Community (DFG).
W.M.P. van der Aalst et al. (Eds.): BPM 2003, LNCS 2678, pp. 370–379, 2003.
c
Springer-Verlag Berlin Heidelberg 2003
ADEPT Workflow Management System 371
2 Features of the ADEPT WfMS
WF Modeling: ADEPT offers advanced concepts for the modeling, analysis,
and verification of WF templates [5]. It enables the explicit definition of control
and data flow, actor and resource assignments, temporal constraints, and pre-
planned exceptions (e.g., forward and backward jumps [6]). This can be done in
an integrated and consistent manner. Thereby ADEPT guarantees static and dy-
namic correctness properties (e.g., no missing input data when invoking activity
programs, no undefined work assignments, no deadlocks), which is an important
prerequisite for later model as well as instance changes. For control flow mod-
eling, a simple, yet powerful formalism is offered. It is based on serial-parallel
graphs with several important extensions necessary to adequately capture real-
world processes. Nevertheless the resulting WF models are easy to understand
for designers as well as for end users. In addition to this graph-based represen-
tation, a precise formal semantics, an equivalent operational semantics, and an
efficient implementation exists.
Temporal Constraints: The handling of temporal constraints is an im-
portant feature of any WfMS. In ADEPT, designers can specify minimal and
maximal durations for WF activities. At runtime, in addition, appointments may
be associated with them. Furthermore, time dependencies between activities are
definable (e.g., ”Xmust be completed 2 days before Ystarts”). ADEPT offers
advanced concepts for specifying such constraints and for checking already at
buildtime whether they are satisfiable or not [2]. Currently, we use Temporal
Constraint Networks for representing time constraints and for checking consis-
tency. At runtime, ADEPT schedules activities according to their starting times,
supervises temporal constraints, and informs users when deadlines are going to
be missed. Problems we have to deal with in this context include uncertainty,
delays, and temporal inconsistencies (e.g., due to model changes).
Ad-hoc WF Changes: The support of ad-hoc changes is a must for WfMS
in order to cover a broad spectrum of processes. At the instance level, ADEPT
enables different kinds of ad-hoc deviations from the pre-modeled WF template
(e.g., to omit activities, to change activity sequences, or to insert activities [5]).
Such dynamic changes, however, must not lead to an unstable system behav-
ior; i.e., none of the guarantees which have been achieved by formal checks at
buildtime must be violated due to the dynamic change. ADEPT ensures this by
introducing formal pre- and post-conditions for change operations. In particular,
a consistent state must be preserved when a WF instance is going to be adapted.
Additionally, ADEPT properly integrates changes with respect to authorization
and documentation. Furthermore, all complexity associated with the adaptation
of WF instance states, the re-mapping of input/output parameters of the com-
ponents affected by a change, the problem of missing input data due to activity
deletion, or the problem of deadlocks is hidden to a large degree from users.
WF Schema Evolution: In order to adequately deal with business pro-
cess changes it is important that adaptations can be quickly performed at the
WF type level as well. Besides versioning, ADEPT supports the propagation of
WF type changes to in-progress WF instances. In doing so, change propagation
372 M. Reichert, S. Rinderle, and P. Dadam
is restricted to those WF instances for which the type change does not con-
flict with current instance state or previous ad-hoc changes. Basic to this is a
comprehensive framework for change propagation which is based on well-defined
compliance criteria for WF instances and on advanced rules for automatically
and efficiently adapting instance markings.
Specification and Synchronization of Inter-WF-Dependencies: Many
WfMS do not provide adequate means for (semantic) inter-workflow coordination
as concurrently executed WF instances are considered completely independent.
Though WF templates are modeled separately from each other in order to re-
main comprehensible and manageable, very often corresponding instances are
semantically inter-related in the one way or another [4]. Pragmatical approaches
like inter-workflow message passing or merging interdependent workflows within
one template do not satisfactorily solve this problem. The latter, for example,
would lead to a large number of templates, each of them very complex and
hard to maintain. ADEPT uses interaction expressions and interaction graphs
as a simple yet powerful mechanisms for the specification and implementation of
inter-WF dependencies [4]. In addition to a graph-based semi-formal interpreta-
tion, a precise formal semantics, an equivalent operational semantics, an efficient
implementation, and detailed complexity analyses exist, which allow us to ac-
tually apply this formalism to coordinate inter-WF dependencies. ADEPT uses
different coordination and subscription protocols to actually employ interaction
expressions for the efficient synchronization of concurrent workflows.
Scalability and Distributed WF Control: In large-scale, enterprise-wide
application scenarios, performance is a critical issue. Due to the high amount of
communication between server(s) and clients the communication network may
become a bottleneck, especially if a large amount of ”long-distance” communi-
cation occurs. To avoid bottlenecks, ADEPT allows to reduce the network load
by partitioning WF graphs and by migrating the control of WF instances from
one server to another during run-time [7,8]; i.e., a WF instance may no longer
be controlled by only one WF server. When performing such a migration, a de-
scription of the instance state is transmitted to the target server. This includes
information about activity states as well as WF relevant data. To avoid unneces-
sary communication between servers, ADEPT allows to control parallel branches
of a WF instance independently from each other (at least as no synchronization
due to other reasons, e.g., a dynamic WF change, becomes necessary).
When designing these features, the following issues have been of interest: How
to maintain robustness and correctness, how does the feature affect application
programming, and how is it made available to the end user? In addition, we have
identified the interdependencies existing between them and we have shown how
the different features work in conjunction with each other.
3 ADEPT Components, Architecture, and Interfaces
We have realized the described features in the ADEPT WfMS. This research
prototype supports WF control and monitoring, demonstrates the feasibility of
ADEPT Workflow Management System 373
dynamic WF changes in a (distributed) WfMS, deals with temporal constraints,
shows which user and programming interfaces are required, and proves that the
concepts work in conjunction with each other as well. All system components
have been implemented in Java, for communication Java RMI has been used.
3.1 ADEPT Buildtime Components
The ADEPT buildtime components enable the definition and management of
WF templates, the description of inter-WF dependencies, the modeling of or-
ganizational entities, the specification of security constraints (Who is allowed
to perform a particular WF change?), and the plug-in of application compo-
nents. All relevant information is stored in the ADEPT repository. In addition,
XML-based descriptions of model data may be generated; e.g., to export tem-
plate descriptions to foreign tools or to exchange them between different WF
servers. However, we do not support the XPDL syntax as defined by the Work-
flow Management Coalition (WfMC). On the one hand, the ADEPT WF meta
model comprises several elements not captured by XPDL, on the other hand the
support of WfMC standards does not have top priority in our research project.
For the modeling and management of WF templates, ADEPT offers a syntax-
driven, graphical WF editor. A sample screen is depicted in Fig. 1. Its upper part
shows a control flow window whereas the lower part displays input parameters of
a selected activity and their mapping to WF data elements (data flow). Activity
attributes are displayed in the right window. To each activity node a (reusable)
template can be assigned. It sets out default properties like minimal/maximum
duration, actor assignments (e.g., based on user roles), associated application
components, and user-defined attributes. The WF designer is supported in cor-
rectly modeling and changing WF templates, i.e., static and dynamic WF prop-
erties as mentioned in Section 2 are guaranteed. To achieve this, the WF editor
enables on-the-fly checks during WF editing as well as complete model checks
initiated by the designer. In any case, a new WF template may only be released
if all checks are successful. This is crucial for the WfMS to achieve a reliable
and stable execution behavior. It is also a prerequisite for dynamic WF changes.
Finally, new releases of a WF template are introduced by deploying the template
to all relevant WF servers. For this, an XML-based description is sent to them
and imported into their run-time databases.
ADEPTdistribution, the distributed variant of the ADEPT WfMS, addition-
ally provides support for assigning WF servers to WF activities. This WF graph
partitioning can be done manually or automatically by the use of a configuration
tool. In the latter case, we make use of repository information (e.g., roles and
locations of users) in order to determine optimal server assignments (i.e., to a
find a partitioning which minimizes overall communication costs at run-time).
Taking our example from Fig. 1, WF instances will be controlled by WF servers
s1and s2. (Server assignments are displayed below the activity nodes. Accord-
ingly, “perform examination” and “write report” are controlled by s2, whereas
all other activities are carried out by s1.)
374 M. Reichert, S. Rinderle, and P. Dadam
5 5 5
5 5
5 5
Fig. 1. ADEPT Workflow Editor
ADEPT provides several other buildtime components for defining different
aspects of process-oriented information systems:
– ADEPT interaction editor: Powerful tool for defining and managing
inter-workflow dependencies based on interaction expressions and graphs [4].
– ADEPT organization modeler: Graphical tool for describing organiza-
tional entities (e.g., user roles, capabilities, and organizational units) and
their relationships (incl. substitution rules).
– ADEPT application configuration tool: This tool allows the WF de-
signer to assign different application components to the same acitivity tem-
plate. In doing so, the concrete binding of a component at runtime can be
based on user as well as on workstation profiles.
3.2 ADEPT Runtime Clients
ADEPT comprises standard runtime clients for end users as well as for system
and process administrators. These clients enable worklist display and manipu-
lation, WF monitoring, activity program execution, dynamic WF changes, and
system configuration.
For worklist handling, several client programs are available. Besides ”thick”
clients, ADEPT offers a Web client interface whose implementation is based on
servlets. Web clients have a limited functionality when compared to standard WF
clients, in particular concerning activity implementation. Both, thick and thin
clients, however, already provide user interfaces for dynamic changes, giving end
users the possibility, at run-time, to deviate from the pre-modeled task sequence.
In detail, authorized actors may intervene into WF control by inserting, deleting,
or shifting activities. In doing so, respective clients provide the necessary change
context and allow change definition at a high semantic level. In particular, end
users are not burdened with the complexity of dynamic changes; i.e., they must
not deal with the problem of missing input data, the avoidance of deadlocks, or
the graph transformations and state adaptations necessary to realize the change.
ADEPT Workflow Management System 375
To monitor in-progress WF instances and to demonstrate the effects of dy-
namic changes, ADEPT offers a special monitoring client. It allows authorized
users to visualize WF instance graphs, together with the information related to
them. Fig. 2 shows a sample screen of a WF instance created from the template
as depicted in Fig. 1. Activities “admit patient”, “instruct patient”, and “collect
patient data” have been completed (indicated by symbol √), whereas activity
“calculate dose” is currently activated (indicated by symbol ✷). Fig. 2 also dis-
plays data elements read and written by the selected activity (“calculate dose”
in the example) as well as detailed information about this activity (e.g., actor
and server assignments, starting time, priority, etc.). All relevant information
is managed by the WF server which controls this activity (s1in the example).
Actually, the monitoring client only shows the WF instance graph from the view-
point of server s1(to which it is connected). Normally, this server does not know
how far the execution in the upper branch of the parallel branching (currently
controlled by s2) has proceeded.
Fig. 2. ADEPT Monitoring Client (before the dynamic change of a WF instance)
Let us sketch how a dynamic change of the (distributed) WF instance from
Fig. 2 is realized:
Example: Assume that an authorized user (connected to s1) specifies that activ-
ity “perform allergy test” is to be inserted between node sets {“instruct patient”}
and {“write report”, “produce drug”}; i.e., the allergy test shall be performed af-
ter patient instruction and before reporting and drug production. The resulting
WF instance graph is depicted in Fig. 3. Internally, the change is accomplished
as follows: First of all, to decide whether the insertion is permissible or not,
s1retrieves information about the global state of the WF instance from other
active servers (s2in our example). As a result, s1finds out that activities “write
report” (controlled by s2) and “produce drug” (controlled by s1itself) have
not been started yet; thus the dynamic insertion is allowed. In the following,
s1performs all necessary graph transformations to realize the change. It inserts
376 M. Reichert, S. Rinderle, and P. Dadam
activity “perform allergy test” parallel to the minimal block, which contains
the nodes “instruct patient”, “write report”, and “produce drug”. (For this, the
AND split n1, which represents a null task, is inserted). To enforce the desired
control dependencies, three synchronization edges are added (e.g., the edge link-
ing “perform allergy test” with “write report”). Finally, the state of the newly
inserted activity is evaluated, leading to its immediate activation.
Fig. 3. ADEPT monitoring client (after the WF instance change)
3.3 ADEPT System Architecture and Programming Interfaces
The ADEPT WfMS is based on a multi-server architecture (cf. Fig. 4). A WF
instance may either be controlled by a single server or by multiple servers if favor-
able. To each server different clients can be connected, e.g., worklist programs,
monitoring components, and modeling tools. For implementing non-standard
clients, ADEPT offers a rich API. It extends the one-directional client-server
communication in order to enable WF servers to play an active role if need be;
e.g., to initiate requests at the client site in order to get approvals from WF par-
ticipants when performing a change or to immediately notify users when dead-
lines are going to be missed. Which communication model is used depends on the
application scenario and can be configured by developers. Inter-WF dependen-
cies are controlled by an interaction manager, which uses suitable coordination
protocols to ensure that a client does not execute an action which is currently
not permitted according to some inter-workflow dependency.
Server implementation is based on relational DBMS, which enables trans-
actional execution of requests and, therefore, guarantees persistency and con-
sistency of model and instance data. The kernel of the WF server is realized
as a multi-layered architecture. The top level, the Execution Layer, processes
client API calls (e.g., to start an activity or to perform a change). Each call
is decomposed into a set of service requests from the underlying Service Layer,
which comprises services designed along the described features (e.g., for schedul-
ing WF activities, dynamically changing WF instances, managing user worklists,
ADEPT Workflow Management System 377
ADEPT
Server
Kernel
(WF APIprocessing)
Execution Layer
DBMS
(Oracle)
Distribution Layer
Data Access Layer
Application
Databases
Time
Management
Server-t o-Ser v er-
Communica ti on
(synchronous&
asy nc hr o no us )
Service Layer
Input
Queue
Output
Queue
Processes/Threads
Service
Request
Proces ses /Threa ds
Name and Directory Service
Input
Queue
Application Interface
WF Task
Manager
WF-
Client-
API
Service
Result
Active
Notification
ADEPT
Server
WFdata
Workflow
Applications
ADEPT Demo Client
ADEPTeditor
ADEPTorganager
Fig. 4. ADEPT System Architecture
or handling temporal constraints). As an example take an activity completion,
which leads to an update of the time schedule and the state of the respective WF
instance, a role resolution of subsequent steps, and an update of worklists. Each
component of the Service Layer itself decomposes calls into basic operations for
the Data Access Layer (e.g., to read, to create, or to modify WF objects). Fi-
nally, if a migration of the WF control or a synchronization of the WF data
becomes necessary, the Distribution Layer provides the required functionality.
ADEPT provides rich programming interfaces whose functionality goes far
beyond the WfMC API. The offered change operations hide as much of the com-
plexity of a dynamic change from application programmers as possible. Regard-
ing activity insertion, for example, the method dynamicInsertBetweenNodes
can be used: For a given WF instance, a new activity (with id actIdentifier
and activity template actTemplate) can be inserted between node sets
predNodes and succNodes. Information on how to map activity parameters
to process data elements can be passed by the parameter maInfo. ADEPT
allows different settings, e.g., automatic mapping of parameters to existing
data elements or provision of input parameters by automatically generated,
electronic forms.
public class WFProcessInstance {
public WFModificationResult dynamicInsertBetweenNodes(
ActivityTemplate actTemplate, ActivityId actIdentifier,
InsertionArea predNodes, InsertionArea succNodes, ModificationAdjustInfo maInfo)
// other methods
}
4 Practical Use and Lessons Learned
To gain concrete implementation and usability experience we have elaborated
ADEPT within several research projects. Some of them have been carried out
by our department in close cooperation with partners from different application
378 M. Reichert, S. Rinderle, and P. Dadam
domains. Additionally, we deployed the ADEPT WfMS to other research groups
who have used it as platform for implementing sophisticated WF scenarios. In
summary, all these projects helped us to identify basic needs for adaptive work-
flows and to evolve the ADEPT WfMS over time. Current projects working with
ADEPT include CONSENSUS [1], AgentWork [3], and WebFlow [9].
Clinical workflows: We consider hospital processes as being one of the
most challenging application areas for WF technology [2]. Typically, a hospital
comprises decentralized units which participate in a variety of medical and or-
ganizational procedures with different complexity and duration (up to several
months). In a two-years WF project with a Women’s Hospital, we performed an
in-depth analysis of all characteristic WF types, the organizational structures
and responsibilities related to them, the kinds of exceptions which may occur,
and the adequate reactions necessary to deal with them. The identified require-
ments helped us to design the basic features of the ADEPT WfMS and to get
an impression of the change facilities needed. In order to gain concrete experi-
ence with the use of WF technology in general and with the ADEPT WfMS in
particular we implemented selected clinical processes based on them. The goal
was to learn how computer-based process support can be smoothly integrated
in the daily routine work and how adequate user interfaces have to look like. As
a result, it became obvious that WfMS with a proper, secure, and robust han-
dling of exceptional cases are a mandatory prerequisite for any WF-based clinical
application. ADEPT has been perfectly coherent with these requirements.
Automatic WF adaptations: AgentWork [3] offers a system for auto-
matically adapting WF instances. For this, a rule-based approach has been
applied. When exceptional events occur, AgentWork identifies WF instances
to be adapted, determines the change operations to be applied, automatically
performs the change, and notifies WF participants accordingly. AgentWork has
adopted the ADEPT meta model and has used the ADEPT WfMS as implemen-
tation platform. It benefits from the offered features, in particular concerning
WF modeling and execution, ad-hoc changes, and temporal constraint manage-
ment. Apart from this, we had received important feedback which helped us to
evolve the ADEPT user and programming interfaces. Currently, with WebFlow
another project of this group is on its way [9]. It aims at the flexible support of
cross-organizational workflows. Due to its dynamic change facilities, the ADEPT
WfMS will be a core component of WebFlow as well.
Flexible E-negotiations: CONSENSUS offers a flexible support system
for e-negotiations based on parameters like quality, delivery, or warranty [1]. E-
negotiations are required, for example, in conjunction with supply chains and
e-procurement. On the one hand they have to be organized in a process-oriented
manner, on the other hand they require flexibility and dynamism to accommo-
date to the various contingencies and obstacles that can appear during negoti-
ation. For example, if a supplier or a shipping company makes a new offer that
might be of interest for a buying company, the buyer will review negotiation
activities already planned within the WF model and may want to rearrange
them (e.g., to dynamically skip, replace, or shift activities). In this context, the
ADEPT change and verification facilities have proven as perfectly coherent with
ADEPT Workflow Management System 379
the flexibility requirements in e-negotiations. However, there are several require-
ments identified within the CONSENSUS project (e.g., dynamic change of WF
attributes) which have not yet been fully supported by ADEPT (see [1]).
5 Summary
The ADEPT WfMS is the technological answer to the requirements set out by
real-world processes. We have implemented fundamental concepts related to WF
modeling, dynamic changes, temporal constraints, inter-WF dependencies, and
scalability in a powerful research prototype. Currently, the integration of change
propagation facilities in connection with WF schema evolution is on its way.
The lessons learned from the sketched application projects have helped us to
further develop the underlying concepts of the ADEPT WfMS, to improve and
complement its buildtime and runtime components, and to refine user as well
as programming interfaces. Adaptive WF technology as offered by ADEPT will
be core of future WfMS and significantly influence the development of process-
centered applications. It will drastically simplify application programming by
providing rich, high-level interfaces for defining and changing model as well as
instance data. As a consequence, development and adaptation times can be re-
duced by factors when compared to current ”hard-wired” solutions.
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