=Paper=
{{Paper
|id=Vol-3758/paper-32
|storemode=property
|title=Towards Object-centric BPMN Process Models
|pdfUrl=https://ceur-ws.org/Vol-3758/paper-32.pdf
|volume=Vol-3758
|authors=Anjo Seidel,Maximilian König,Mathias Weske
|dblpUrl=https://dblp.org/rec/conf/bpm/SeidelKW24
}}
==Towards Object-centric BPMN Process Models==
https://ceur-ws.org/Vol-3758/paper-32.pdf
Towards Object-centric BPMN Process Models
Anjo Seidel1,∗ , Maximilian König1 and Mathias Weske1
1
Hasso Plattner Institute, University of Potsdam, Prof.-Dr.-Helmert-Str. 2-3, 14482 Potsdam, Germany
Abstract
BPMN, the de facto standard for business process modeling, is designed to model activities and control flow
for a specific case notion. The new paradigm of object-centric process mining proposes to discover process
models that are not bound to one specific case notion, but rather define a process as the combined behavior of
the involved data objects. In that context, different process modeling approaches aim to depict object-centric
behavior. However, the object-centric capabilities of BPMN have not yet been evaluated. Therefore, this paper
investigates to what extent BPMN supports object-centric modeling features from literature. We show that the
semantics of BPMN process models are insufficient to depict object-centric processes. To overcome the identified
limitations, we rely on concepts from prior work on case management to propose the new notion of object-centric
BPMN process models.
Keywords
Business process modeling, Object-centric processes, BPMN 2.0, fragment-based Case Management, Object-centric
Petri nets with Identifiers
1. Introduction
The OMG standard Business Process Model and Notation (BPMN) is well-established in practice and
the most widely used process modeling language [1]. Like most traditional activity-centric process
modeling approaches, BPMN relies on a single case notion [2], i.e., a specific perspective on the process,
to define control flow relations between activities that are relevant for reaching business goals [3]. To
represent the interaction of activities with business objects, data objects can be modeled.
The new trend of object-centric process mining proposes a more comprehensive perspective on
business processes by identifying relevant business objects and their individual behavior [2]. Based
thereon, the different objects can be correlated through activities that operate on sets of objects.
Currently, most approaches to define and visualize “object-centric process models” are based on Petri
nets [4], while more high-level process modeling approaches have been introduced under the term
“data-centric process models”. An overview of the latter is presented by Steinau et al. [5]. Van der
Aalst [6] already motivates the refinement of BPMN to better capture object-centric behavior. Yet, the
current capabilities of BPMN are not analyzed, and possible adjustments are not specified.
This paper analyzes object-centric capabilities of BPMN by referring to requirements and charac-
teristics from literature. Our investigation shows that BPMN lacks flexibility and precise semantics
for identifying and correlating data objects. This indicates the need for object-centric BPMN process
models (OC-BPMN); an approach that capitalizes on BPMN’s comprehensibility and the holistic behavior
represented in contemporary object-centric process modeling approaches. To model OC-BPMN process
models, this paper proposes a graphical modeling language combining BPMN process fragments with a
data model. It bases its concepts on prior work on fragment-based case management [7].
In the remainder of this paper, we first discuss related work in section 2. We analyze the object-centric
capabilities of the status quo of BPMN in section 3, before introducing the novel OC-BPMN process
models and informally describing their semantics in section 4. Finally, section 5 discusses the proposed
approach and concludes the paper.
Proceedings of the Best BPM Dissertation Award, Doctoral Consortium, and Demonstrations & Resources Forum co-located with
22nd International Conference on Business Process Management (BPM 2024), Krakow, Poland, September 1st to 6th, 2024.
∗
Corresponding author.
Envelope-Open anjo.seidel@hpi.de (A. Seidel); maximilian.koenig@hpi.de (M. König); mathias.weske@hpi.de (M. Weske)
Orcid 0000-0002-9652-5340 (A. Seidel); 0000-0002-2244-1179 (M. König); 0000-0002-3346-2442 (M. Weske)
© 2024 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR
ceur-ws.org
Workshop ISSN 1613-0073
Proceedings
2. Related Work
The object management group defines the standard BPMN 2.0 [8], which is one of the most widely
used process modeling approaches [1]. To provide clear execution semantics, Dijkman et al. [9] provide
translational semantics of control flow structures to Petri nets without considering data objects at all.
Building thereon, mappings to Petri nets considering data objects and states [10] and BPMN input
and output sets [11] have been proposed. Making use of the additional expressiveness of colored Petri
nets, Ramadan et al. cover more complex BPMN constructs such as subprocesses and multi-instance
behavior, but mostly neglect complex data interactions with these elements [12]. Extending on BPMN,
Meyer et al. [13] introduce the concept of foreign keys between data objects and translate data pre- and
postconditions to SQL queries, thus assigning meaning to data objects and data associations. König and
Weske provide formal execution semantics for multi-instance behavior on data [14].
Building on the notation of BPMN, Hewelt et al. propose fragment-based case management [7], a
hybrid modeling approach that combines imperative control flow between activities and declarative
data flow between process fragments. The semantics are formalized as colored Petri nets by Haarmann
et al. [15].
Existing high-level process modeling approaches already aim to represent object-centric behavior.
Steinau et al. [5] provide an overview and a framework to systematically analyze the capabilities of
data-centric process modeling approaches. For instance, Philharmonic Flows [16] define object-centric
behavior, which can be transformed into BPMN 2.0 [17].
More recent process modeling approaches extend on Petri nets to represent object-centric processes.
Gianola et al. [4] provide an analysis identifying object-centric modeling features. Synchronous Proclets,
as presented by Fahland [18], allow describing the behavior of different object types. Transitions
referring to events that interact with different object types are associated. Evolving from 𝜈-Petri
nets [19], Petri nets with identifiers (PNID) [20] support the identification of individual objects and
their links. In the context of process mining, van der Aalst and Berti propose object-centric Petri nets
(OCPN) [21] that define variable arcs to transfer a variable number of tokens at once but lack object
identification. Combining the concepts of OCPNs and PNIDs, Gianola et al. [4] propose object-centric
Petri nets with identifiers (OPID) that overcome the limitations of the prior Petri net approaches. Analog
to PNIDs, they represent object identities and object relations, while variable arcs can transfer a variable
number of object identities.
3. Object-centricity in BPMN process models
The previous section outlines contemporary object-centric process modeling approaches. To investigate
the capabilities of BPMN, we refer to a set of modeling features for object-centric process models
as described by Gianola et al. [4]. The results of comparing OCPN [21], PNIDs [20], OPIDs [4],
BPMN [8] and the novel OC-BPMN are presented in Table 1. Furthermore, the issues of convergence
and divergence [2] are discussed from a process modeling perspective.
3.1. Object-centric process modeling features
Object-centric process models need to allow for object creation and object deletion, e.g., in the order
management process, it should be possible to create new orders and also to delete them. The existing
Petri net-based data semantics for BPMN [10, 11] support object creation. Object deletion can be
modeled implicitly through final data states. An order can be considered completed and is therefore
unavailable for further processing. The modeling feature multi-object spawning and transfer describes
the capability to create and operate on lists of data objects. As described by König et al. [14], BPMN is
capable of iteratively creating items for an order. They are added to a list, just like in OPIDs.
BPMN is not yet able to represent object references to distinguish individual object instances. In
existing formalizations, objects are represented as anonymous tokens. In the example, orders and
items cannot be identified via IDs. Hence, their links cannot be identified either and object relations are
not supported. Synchronization describes the ability to remember the object relations throughout the
process. Items of different orders should not be mixed up. As BPMN cannot represent links between
objects, there are no means to correlate objects at different points of the process.
Concurrent object flows describe the ability to process objects concurrently and independently of each
other. BPMN supports this feature only partially through multi-instance subprocesses. Given a list data
object, each element can be processed by a different subprocess instance concurrently. Yet, the parent
process needs to wait for the termination of all subprocess instances.
Table 1
Overview of supported (3), unsupported (7) and partially supported (∼) modeling features for object-centric
process modeling approaches (adapted from [4]).
object object concur. multi-object object synchro- object
creation removal object flows transfer relations nization reference
OCPN 3 3 3 3 7 7 ∼
PNID 3 3 3 ∼ 3 ∼ 3
OPID 3 3 3 3 3 3 3
BPMN 3 3 ∼ ∼ 7 7 7
OC-BPMN 3 3 3 3 3 3 3
3.2. Convergence and Divergence in BPMN
In addition to the elaborated modeling features, we investigate the issues of convergence and divergence,
as described by van der Aalst [2] in the context of process mining.
Divergence occurs in one-to-many relations between the case object, which determines the case
notion, and other related objects. As illustrated in Figure 1 (left), the case notion of the order requires a
multi-instance behavior for all related items.
Convergence, on the other hand, describes the issue that a case notion is the subject of a many-to-one
relation. BPMN cannot concisely represent multiple process instances that share an activity. In the case
notion of an item in Figure 1 (right) the activity place order is executed for every item, but from an order
perspective, it processes multiple items at once. Traditionally, batch processing [22] aims to address this
issue. These limitations stemming from case-centric process models prevent truly concurrent object
flows.
Figure 1: An excerpt of an order management process as BPMN process diagrams in the case notion of an order
(left) and an item (right).
To overcome the limitations of traditional BPMN, we propose object-centric BPMN (OC-BPMN), which
bases its concepts on fragment-based case management (fCM) [7]. In this approach, the traditional
monolithic control-flow structure of BPMN is split into process fragments that each represent an
individual object perspective. As later shown in Figure 3, the order management process can be modeled
as three process fragments, one for the case notion of an order, one for items, and one for routes.
During execution, these fragments can run repeatedly and concurrently and are only constrained by
the availability of data objects. The use of fragments also overcomes the need for sub-processes to
handle divergence and batch activities for convergence.
4. Object-centric BPMN Process Models
To overcome the limitations of traditional BPMN as discussed in section 3, we propose object-centric
BPMN (OC-BPMN), which bases its concepts on fragment-based case management (fCM) [7]. In this
approach, the traditional monolithic control-flow structure of BPMN is split into process fragments
that each represent an individual object perspective. For fCM, a translational semantics to colored Petri
nets defines object identities, and their correlation [15]. As shown in Figure 3, the order management
process can be modeled as three process fragments, one for the case notion of an order, one for items,
and one for routes. During execution, these fragments can run repeatedly and concurrently and are
only constrained by the availability of data objects. OC-BPMN combines four modeling artifacts: (i) a
data model defining the available object types and their associations, (ii) object lifecycles for each object
type that describe the states and state transitions of data objects, (iii) process fragments with a BPMN
syntax, and (iv) an object diagram as a representation of the current data state of a running OC-BPMN.
4.1. Data Model
Analog to OPIDs and OCELs, OC-BPMN defines a set of possible data object types as a data model. For
the example order management process, the UML class diagram [23] on the left-hand side of Figure 2
describes the classes for orders, items, and routes. Additionally, it defines associations between classes.
An order can have many items, and many items can be correlated to one route.
In line with OPIDs [4], we restrict our class diagram to binary associations and prohibit many-to-
many relations. Many-to-many relations can be represented using association classes and reification.
Note that orders, for example, have an implicit many-to-many relation to routes.
Figure 2: The UML class diagram (left) and the respective object lifecycles for each class (right) for the order
management process.
4.2. Object Lifecycles
Analog to BPMN [13] and fCM [7], OC-BPMN specifies an object lifecycle (OLC) for each data class.
An OLC defines a set of states as an abstraction of concrete attributes or processing states. Also, state
transitions are defined. According to the OLCs in Figure 2, an order can be new, then placed, invoiced
before being paid, and finally completed. In the same manner, the available states and transitions are
defined for items and routes. An item can initially be new, placed, picked, in delivery, shipped, and
completed. A route is either new, started, or ended.
4.3. Process Fragments
In OC-BPMN, concurrently running process fragments jointly define the object-centric process. As
illustrated in Figure 3, the order management process can be expressed as three fragments. Within
a fragment, activities can be connected via traditional control flow, which orders their execution.
Additionally, activities read and write data object nodes and list data object nodes that specify a class
from the class diagram and a state from its corresponding object lifecycle. Following established BPMN
semantics [24], activities can be executed if they are both control flow (cf) and data flow (df) enabled. An
activity is cf-enabled without ongoing cf-arcs or if at least one has been enabled by previous activities.
It is df-enabled in an execution state if data objects in the specified states exist with the required links.
In the order fragment, start shopping is always enabled and creates a new object instance of Order in
state new. Given a set of new items, place order is then enabled for items and the new order. It will
change the items and the order into the state placed respectively. Furthermore, the transferred items are
all linked to the order to reference them later. Then the order can be invoiced and paid by the fragment.
Concurrently, the individual items are processed in the item fragment, and can be correlated to routes
and processed further in the routes fragment.
Figure 3: The object-centric BPMN fragments representing the order management process.
In OC-BPMN, we introduce a new notation to specify the required synchronization of related
objects. Object nodes can be associated to indicate that the execution of the following activity requires a
synchronization of the referenced objects at runtime. For instance, the node for Order[paid] is associated
with the list data object node for Item[shipped]. The activity mark as complete can, therefore, only be
executed for orders and items in the respective states and only if they have been linked before. After
the execution, the links will be preserved. Analogously, end route synchronizes a route with its items.
4.4. Data State
With OC-BPMN, we also propose a notation for the instance level of an OC-BPMN model. The data
state is an instance of the class diagram. It represents objects as class instances with a state attribute of
their respective OLC. Objects can be linked, such that each link is an association instance.
In Figure 4, a UML object diagram [23] depicts the data state containing the paid order 𝑜1 and placed
order 𝑜2, the items 𝑖1 (shipped), 𝑖2 (picked), and 𝑖3 (placed), and the ended route 𝑟1 and new route 𝑟2.
Also note that 𝑜1 is linked to multiple items, i.e., 𝑖1 and 𝑖2, and 𝑜2 is linked to 𝑖3. In the current state,
only 𝑟1 is linked to 𝑜1. In a future data state, 𝑟2 could be linked to 𝑖2 and 𝑖3, constituting an implicit
many-to-many relation between order and route.
An object diagram can be useful to visualize the current state of a running process or to configure an
initial data configuration for simulating or executing the OC-BPMN.
Figure 4: The UML object diagram depicting an instance of the class diagram (cf. Figure 2) for the order
management process.
5. Discussion & Conclusion
This paper investigates the capabilities of BPMN to model object-centric processes. In our analysis of
modeling features, we identify limitations for BPMN regarding object identification and missing link
semantics. Also, the case notion of BPMN process models leads to the problems of convergence and
divergence. To overcome these limitations, we build on concepts from case management to propose the
novel modeling paradigm of object-centric BPMN (OC-BPMN).
OC-BPMN models can flexibly combine process fragments that are modeled with different case
notions, i.e., object perspectives, allowing to overcome convergence and divergence in process modeling.
In the future, we will provide precise execution semantics for OC-BPMN. Object-centric Petri nets with
identifiers by Gianola et al. [4] promise a suitable goal formalism, which can be extended with exact
synchronization as proposed for Proclets [18]. The resulting formalism will allow for precise correlation
mechanisms of linked data objects throughout the process execution.
So far, we only analyzed BPMN and not other contemporary object-centric process modeling ap-
proaches that could also provide useful visualizations for object-centric processes. Future studies should
investigate their capabilities as well and compare their comprehensibility for users empirically.
In the future, contemporary discovery algorithms for OCPNs can be extended to also allow for
discovering the proposed OC-BPMN models. This includes a discovery of the creation of links between
objects and their synchronization behavior. On the other hand, OC-BPMN models could also be used
and configured to model and refine object-centric simulation models, allowing for the creation of
object-centric event logs.
In summary, we propose a novel, object-centric dialect of BPMN with execution semantics based
on OPIDs. We believe that OC-BPMN offers a more well-known notation for object-centric processes,
making the object-centric paradigm more accessible in practice.
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