FINDING REUSABLE BUSINESS PROCESS MODELS
BASED ON STRUCTURAL MATCHING
Han G. Woo
Le Moyjne College, 1419 Salt Springs Road, Syracuse NY 13214, U.S.A.
Keywords: Business process models, Reuse, BPMN, Structural data mining.
Abstract: Successfully integrating business processes with information systems has been a critical issue in many
organizations. Such integrations should take place throughout the various stages of systems development to
manage correct, traceable business process requirements. To support business process management (BPM)
activities, many modeling formalisms and tools were proposed. Yet reuse of business process knowledge
has been understudied although reuse practice is common, often relying on human recollection and
reference models. This research proposes a tool support that assists reuse of business process models such as
BPMN, EPC, and UML Activity Diagrams. In the suggested approach, the semantics of these formalisms
are preserved in the conceptual graph format along with their instantiations and interrelationships. A
structural data mining tool is then used to find reusable process models based on similarities in sequences of
events and processes. This study can be applied to many reuse-related situations, namely retrieval of
reusable process models given a problem, discovery of sequence patterns among process models, and
suggesting the instances of (anti-) patterns for learning purpose.
1 INTRODUCTION
Since the management trend of business process
reengineering in the 1990s, business process
management (BPM) has been a critical issue in
many organizations (Smith and Fingar 2003). A
business process is loosely defined as a “set of
partially ordered activities intended to reach a goal
(Hammer and Champy 1993),” even though there is
a great deal of variation among its definitions
depending on which aspect of business processes is
of interest: social construct, dynamic system, or
machine metaphor (Lindsay et al. 2003). BPM
becomes more important in the fast-changing digital
economy as organizations’ business processes
themselves evolve over time to keep up with
competitive market pressure. The key aspects of
BPM are to fully comprehend an organization’s
business processes and to manage necessary changes
in these processes to meet the organization’s
strategies. For successful integration of the BPM
practices with enterprise information systems,
various business process (or workflow) modeling
formalisms and tools have been suggested (Stohr
and Zhao 2001; Weske et al. 2004).
As business process models have been analyzed
and accumulated in various projects, reuse of
business process models becomes common in
practice although it often relies on human
recollection and reference models (Thomas et al.
2006). System engineers or subject matter experts
recall business process models that were previously
constructed in a domain similar to their current
project. They search relevant business process
models from their memories or a repository of
archived documents, and then apply retrieved
models to the current context. Reusing business
process models, akin to other analysis and design
artifacts in software development, can bring various
benefits to organizations. Reusable business process
models can facilitate communications between
system engineers and clients instead of starting from
scratch, thereby help organizations capture correct
business process requirements and identify possible
improvements. In this way, they can expedite the
process of business process management to quickly
respond to changing business environments. In
addition, organizations may obtain best-practice
business processes because reusable process models
have been already validated and successfully
integrated in a similar domain.
249
G. Woo H. (2009).
FINDING REUSABLE BUSINESS PROCESS MODELS BASED ON STRUCTURAL MATCHING.
In Proceedings of the 11th International Conference on Enterprise Information Systems - Information Systems Analysis and Specification, pages
249-255
DOI: 10.5220/0002012002490255
Copyright
c
SciTePress
Exploiting potential benefits of BPM appears to
have redrawn attention from researchers in recent
years. It is mainly because of (1) standardization
efforts for business process modeling languages
such as BPMN, BPEL, and XPDL (Dreiling et al.
2008) and (2) shifted interests toward Web-based,
SOA(Service-oriented architecture) business
applications (van der Aalst et al. 2007).
Interoperable business process model specifications
and packaging them as Web services render reuse of
business process not only much easier but more
attractive in that there are more reusable assets
available to organizations and ready for system
integration with slight adaptation.
Yet reuse of business process knowledge has
been understudied compared to all the progress
made in BPM research in the last two decades
(Hidders et al. 2005 ). Most studies related to
process reuse place their focus on utilizing “bigger
chunks” of business processes like process
templates, domain reference models (Thomas et al.
2006), or interoperable services (Brambilla et al.
2006; Distante et al. 2007; O'Brien et al. 2008;
Tarantilis et al. 2008) coupled with business
processes, with little attention to how to find
reusable business processes based on similarities
among actual activity and control sequences.
This research proposes a tool support that assists
reuse of business process models such as BPMN,
EPC, and UML Activity Diagrams. In the suggested
approach, the semantics of these specifications (e.g.,
event, task, sub-process, gateway, sequence,
message, and data object) are preserved in a
conceptual graph format, along with their
instantiations and interrelationships. A structural
data mining tool is then used to find reusable process
models based on similarities in sequences of events,
processes, and control structures. The structural
matching approach can complement other reuse
methods like classification based on descriptors or
attributes of business processes, and domain models.
2 RELATED WORK
Many commercial tools and academic work
implicitly or explicitly provide some reuse support
for business processes based on reusable asset
management or knowledge management perspective.
OMG’s RAS (Reusable Asset Specification)
standard (Object Management Group 2005) provides
guidelines for profiling reusable software asset.
Business process models may be managed in many
forms: requirements, artifacts, diagram, or services
(Park et al. 2007). Another approach to business
process reuse can be found in application of
reference models. MIT process handbook is an
example of such reference models that contains a
comprehensive online library of business process
knowledge (Malone et al. 2003). Thomas et al.
(2006) proposes a reference model management
system (RMMS) that facilitates development and
management of business process reference models.
Some of main ERP vendors also offer BPM tools
for example, SAP’s NetWeaver and Oracle’s Oracle
Workflow that provide customers with workflow
or business scenario templates and process patterns.
These templates are normally used for typical
business processes such as order processing, those
which draw on a reference model of industrial
business practice.
It appears that the increasing popularity of SOA
(Service-oriented architecture) Web applications has
also affected BPM research streams. In SOA,
business processes are bundled with service
architectures and reused as a form of context-aware
services independent of development technologies
and platforms (Brambilla et al. 2006; Distante et al.
2007; O'Brien et al. 2008; van der Aalst et al. 2007).
The commonality among these examples of
process reuse research is that the guidelines for reuse
derive from similar business context, attributes, or
descriptors, not detailed process sequences.
Therefore, little assistance is available to business
process analysts when they seek instance-level
exemplars that can be applied to generate alternative
business processes or to manage dynamic changes in
existing processes.
A few studies in workflow management system
(WfMS) research community attempt to assist in
workflow reuse based on workflow sequences and
control structures. van der Aalst et al. (2003)
suggests generic workflow patterns. These domain-
independent patterns were initially defined using
control flows; the patterns have evolved over time
including the observations of various perspectives in
workflows: data, resource, and exception handling
(N. Russell et al. 2006). Some of the basic control-
flow patterns are used in this study to illustrate
business process queries.
The process mining tool such as ProM (van der
Aalst 2007) aims to discover reusable business
processes from a-posteriori analysis of event logs
that record activities, timestamps, roles, and related
data object. It claims that the discovered patterns
from process mining are more practical and realistic
because it looks at “inside the process” at a very
refined level.
ICEIS 2009 - International Conference on Enterprise Information Systems
250
Madhusudan et al.’s work (2004) employs case-
based reasoning to support workflow modeling and
design. Their framework deals with business process
model management issues, from storage, retrieval, to
reuse and adaptation. To find reusable workflow
cases, a similarity-based case retrieval method called
Similarity Flooding algorithm is used. This
technique shares some characteristics with the tool
support presented in this paper in that it finds
matching two (query and source) directed graphs
based on semantic similarity in node and edge labels
and similarity in topology of the graphs. However
the representation of business process models and
similarity metric in Similarity Flooding are rather
simpler; it does not consider detailed process
elements expressed in standard modeling
specifications.
3 STRUCTURAL MATCHING
This section explains an approach to reuse of
business process models based on structural
similarity. First, a system engineer or reuse
administrator defines or collects business process
models in BPMN, EPC, or UML Activity diagram
notations. These models are transformed into
directed conceptual graphs that consist of vertices
and edges. The conceptual graphs are added into a
business process library along with the initial
models. As an analyst begins defining a business
process model or tries to find applications of a
certain pattern, the analyst can call on the tool
implemented with the data mining algorithm. The
algorithm searches for similar structures in the
library and returns best matches. The analyst then
selects the most relevant business process model and
adapts it to the current analysis problem.
3.1 Structural Data Mining
The tool support suggested in this paper employs an
automated relational learner called Subdue
(Gonzalez et al. 2000; Joyner et al. 2001) that
discovers patterns in structured data sets. In Subdue,
information is stored as a graph of vertices and
edges. Vertices usually refer to objects, attributes,
and their values while edges represent relationships
between the objects. The syntax for vertex
description is <v id label> where id is a vertex
number and label is the name of that vertex. Edges
are coded with <u id1 id2 label> or <d id1 id2
label>. The former represents an undirected edge (u)
between vertex id1 and id2; the latter means a
directed edge (d) from vertex id1 to id2. Examples
of the Subdue graph are shown in Figure 1.c and
Table 1.
Subdue’s search algorithm finds repetitive
substructures called concepts in graphs. The search
starts with a uniquely labeled vertex of a graph
initializing the search queue. Following the beam
search strategy, Subdue expands its search by
including adjacent edges and associated vertex in all
possible ways, yielding potential substructures.
When a repeating substructure is found, it is
replaced with a placeholder vertex pointer to its
substructure, thereby compressing the whole graph.
Each candidate substructure is evaluated by a
compression score. The compression score is
calculated by (DL(S) + DL(G|S)) / DL(G) where
DL(G) stands for the description length of the input
graph, DL(S) the description length of the
substructure, and DL(G|S) the description length of
the input graph when compressed by the
substructure. This evaluation metric bases its
assumption on the Minimum Description Length
(MDL) principle. It states that the best concept
(substructure) describes the whole data set with a
minimal description length, i.e. the length in number
of bits of the graph representation when compressed
by the substructure (Cook and Holder 2000). When a
candidate substructure is found better than others in
terms of the compression ability, it is stored in the
best substructure queue. Iterating this process results
in a hierarchical classification lattice whose lower-
level concepts are included in the higher-level
concepts. The iteration can be limited by two
parameters: breadth of search (beam) and number of
expansions (limit.) The search terminates when it
reaches a user specified limit on the number of
substructures extended or when the search space is
exhausted.
In Subdue, there are two important features
relevant to our purpose. One is its ability to find
inexact match using threshold value. It is especially
useful because finding reusable business processes
normally requires a certain degree of tolerance in
their variations caused by different styles in
authoring models and by differences in naming the
same concept. In Subdue, a threshold value
determines when two structures are similar enough
to match. The analyst can set this threshold
parameter from 0.0 to 1.0. The value 0.0 means a
complete match and 1.0 the maximum tolerance
level. The similarity metric of two structures is
computed as transformation cost / structure size,
where transformation cost is the number of graph
transformations required to make the structures
FINDING REUSABLE BUSINESS PROCESS MODELS BASED ON STRUCTURAL MATCHING
251
isomorphic. Two structures match when the
similarity metric is less than the threshold (Cook and
Holder 2000). The other feature is the capability that
deals with synonyms. A list of predefined synonyms
can substitute different vertex or edge labels that
carry the same meaning. This functionality enables
Subdue’s potential to utilize the benefits of a domain
ontology or lexicon.
3.2 Representation of Business Process
Models
As described in the previous section, business
process models need to be represented as directed
conceptual graphs in order for the structural data
mining algorithm to find a similar match. The
transformation of business process models into
conceptual graphs takes place at two different
abstraction levels: metamodel and instance level.
Since key elements in metamodel types in BPMN,
EPC models, and UML activity diagrams share
similar semantics, converted process graphs can be
used together regardless of differences in the
modeling notations.
Let us consider an example of BPMN models.
BPMN core semantics include swimlanes, events,
activities, gateways, and other artifacts (Object
Management Group 2008). Table 1 summarizes the
representation scheme for BPMN notations. These
metamodel elements are coded with vertices in a
conceptual graph. Each vertex has a label like Pool,
Lane, StartEvent, IntermediateEvent, EndEvent,
Task, SubProcess, Gateway, DataObject, etc. The
connecting objects such as sequence flows and
message connectors are coded as edges between two
vertices that represent these metamodel elements. A
pool or data object instance also becomes a vertex
with its name as a vertex label. Then the instance
and its metamodel vertex are connected with a
directed edge labeled InstanceOf. A task instance
has two vertices describing the nature of the task
with a verb and an object. They are linked with
ActionOf and ActionObjectFor edges respectively.
Gateway instances are coded in a similar fashion.
For example, if there is an exclusive (XOR) gateway
with two branches, a gateway name becomes a
vertex pointing to the metamodel vertex Gateway
with an edge ConditionOf. The two branches are
represented as vertices and connected with edges,
DefaultBranchOf or BranchOf. Figure 1 illustrates a
detailed example of the transformation. Figure 1.a
shows a fragment of the BPMN model, Process
Order while Figure 1.b illustrates the translated
vertices and edges in the conceptual graph format. In
Figure 1.b, the gray-highlighted part represents the
structural information of the process, and the white-
colored elements are the instance-level information.
Figure 1.c is the actual Subdue text graph used in the
algorithm.
The transformation coding scheme is designed
with two guidelines: (1) separation between
metamodel elements and instances and (2)
maintaining an atomic value for each vertex and
edge. These guidelines allow the search algorithm to
focus more on structural aspects of business process
models and to handle naming differences by
populating synonyms. This way, an intermediate
language between natural language and the formality
of first-order logic makes it possible to perform
classification, aggregation, and generalization
(Greenspan and Mylopoulos 1982).
Table 1: Transformation of BPMN into Subdue Graph.
BPMN Semantics
BPMN Example Graph Example
Pool
V 1 Pool
V 2 Sales
D 2 1 InstanceOf
Lane
V 1 Pool
V 3 Lane
V 4 Sales Rep
D 4 3 InstanceOf
D 3 1 Within
MessageStartEven
t
V 1 StartEvent
V 2 Message
V 3 Credit Request
D 2 1 TypeOf
D 3 2 newStateOf
Task
V 1 Task
V 2 Evaluate
V 3 Credit
D 2 1 ActionOf
D 3 2 ActionObjectFor
Gatewa
y
V 1 Gatewa
y
V 2 Approved?
V 3 Exclusive
V 4 Yes
V 5 No
D 2 1 ConditionOf
D 3 1 TypeOf
D 4 1
DefaultBranchOf
D 5 1 BranchOf
Sequence Flow
V 1 Task
V 2 Send
V 3 RFQ
D 2 1 ActionOf
D 3 2 ActionObjectFor
V 4 Task
V 5 Receive
V 6 Quote
D 2 1 ActionOf
D 3 2 ActionObjectFor
D 1 4 Sequence
ICEIS 2009 - International Conference on Enterprise Information Systems
252
a. BPMN model
% Pool
V 1 Pool
V 2 Sales
D 2 1 InstanceOf
% Event
V 3 StartEvent
V 4 Empty
D 4 3 TypeOf
% Task (Receive Order)
V 5 Task
V 6 Receive
V 7 Order
D 6 5 ActionOf
D 7 6 ActionObjectFor
% Gateway
V 8 Gateway
V 9 Exclusive
V 10 Accepted?
V 11 Yes
V 12 No
D 9 8 TypeOf
D 10 8 ConditionOf
D 11 8 DefaultBranchOf
D 12 8 BranchOf
% Task (Close Order)
V 13 Task
V 14 Close
V 15 Order
D 14 13 ActionOf
D 15 14 ActionObjectFo
r
% Sequence Flow
D 1 3 Initiate
D 3 5 Sequence
D 5 8 Sequence
D 11 13 Sequence
c. Graph Text
Pool StartEvent
Sales
Gateway
InstanceOf
Empty
TypeOf
Sequence
Exclusive
TypeOf
Accepted?
Default
BranchOf
Task
Receive Order
ActionOf
Action
ObjectFor
Sequence
Sequence
Yes
No
ConditionOf
BranchOf
Task
Close Order
ActionOf
Fill Order
Task
ActionOf
Sequence
Sequence
Action
ObjectFor
Action
ObjectFor
b. Subdue Graph
Figure 1: Example of Transformation from BPMN to Subdue Graph.
4 PRELIMINARY EVALUATION
To demonstrate the feasibility of the tool support
suggested in the paper, a simple evaluation was
taken with a relatively small process library. It
consists of 37 partially or fully completed business
process models in BPMN notations, yielding 1089
vertices and 1151 edges. The business process
models were collected from the specification
documents, examples available on related Web sites,
and textbooks.
Since the main purpose of this case study is to
see whether the tool can assist in finding similar
business process structures, seven queries were
presented to the library. The queries are borrowed
from the workflow patterns in (van der Aalst et al.
2003), specifically Sequence, Parallel Split,
Synchronization, Exclusive Choice, Simple Merge,
and N out of M Join. These query models are shown
in Figure 3. In addition, the model in Figure 2.a (part
of order processing) is included for a more
complicated query.
For each query, the threshold value is initially set
as 0.0 and then incremented by 0.1 until 0.9. Table 2
summarizes the retrieval results for the queries. In
each trial, relevant, best matched graphs were
retrieved at the threshold between 0.3 and 0.9. For
simple queries like Sequence, Parallel Split, and
Synchronization, the tool was able to find similar
business process models at the relatively low
threshold values. Since the query graphs used simple
labels such as A, B, B1, etc., there was no exact
match found. In the first query Sequence, there are
too many instances found at the threshold > 0.7,
suggesting almost all sequential chains in the library.
For the complicated queries, N out of M Join query
fins only one match at 0.8. The retrieved process
fragment contains an exclusive gateway instead of a
complex gateway. For Process Order query, the
completed business process model was intentionally
prepopulated with a few modifications on vertex and
edge labels, and it was found at 0.8.
The results of the preliminary evaluation suggest
that structural matching technique can be applied to
find relevant, reusable business process models. Yet,
in order for the tool to be practical, each search must
be tuned with a proper threshold. It should be also
noted that for complicated queries with a high
threshold, the computation time may exceed more
than a minute in a personal computer CPU
environment because the algorithm itself is
polynomial. This concern can be resolved by
adjusting other search options such as limit, beam,
number of vertices in a structure, etc.
FINDING REUSABLE BUSINESS PROCESS MODELS BASED ON STRUCTURAL MATCHING
253
Sequence
Synchronization
Simple Merge
Parallel Split
Exclusive Choice
N out of M Join
Figure 2: Workflow Patterns used as Queries.
Table 2: Query Results.
Query Best match found
at threshold
Number of
Instances
Sequence 0.3 – 0.6 > 45
Parallel Split 0.3 – 0.7 > 23
Synchronization 0.3 – 0.7 > 7
Exclusive Choice 0.4 – 0.7 > 11
Simple Merge 0.6 – 0.8 > 9
N out of M Join 0.8 – 0.9 1
Process Order 0.7 – 0.9 1
5 DISCUSSION
This research proposes automated tool support for
business process reuse that exploits rich semantics of
business process modeling formalisms. Business
process models are translated as conceptual graphs
that comprise vertices and edges. The coding
scheme is quite flexible and extensible; it can
express core semantics of existing business process
specifications. By applying the structural matching
technique, the tool support can deal with a certain
degree of informality inherent in business process
models while looking at similar sequence patterns.
This study can be applied to many reuse-related
situations, namely retrieval of reusable process
models given a problem, uncovering sequence
patterns among process models, and suggesting the
instances of (anti-) patterns for learning purpose.
Future work includes developing the prototype of
the tool support, validating its effectiveness in a field
or lab experiment setting. The prototype of the tool
support is under development as a plug-in to SOA
Tools Platform on Eclipse (http://www.eclipse.org/
stp/bpmn.) This approach is being tested with a
bigger collection of business process models for
ERP systems in order to support ERP configuration
with business process modeling. Additional methods
for search tuning also need to be explored to
increase search performance, including ontological
support of important concept matching and Subdue’s
supervised learning feature.
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