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Finding the “Liberos”:
Discover Organizational Models with Overlaps
Jing Yang1, Chun Ouyang2, Maolin Pan1, Yang Yu1( ), and
Arthur H.M. ter Hofstede2
1Sun Yat-sen University, Guangzhou, China
yangj357@mail2.sysu.edu.cn, {panml,yuy}@mail.sysu.edu.cn
2Queensland University of Technology, Brisbane, Australia
{c.ouyang, a.terhofstede}@qut.edu.au
Abstract. Organizational mining aims at gaining insights for business
process improvement by discovering organizational knowledge relevant
to the performance of business processes. A key topic of organizational
mining is the discovery of organizational models from event logs. While
it is common for modern organizations to have employees sharing roles
and responsibilities across different internal groups, most of the exist-
ing methods for organizational model discovery are unable to identify
such overlaps. The overlapping resources are likely to be generalists in
an organization. Existing findings in process redesign best practices have
proven that generalists can help increase the flexibility of a business pro-
cess (similarly to the flexibility of the role of “libero” in certain team
sports). In this paper we propose an approach capable of discovering
organizational models with overlaps and thus helping identify general-
ists in an organization. The approach builds on existing cluster analysis
techniques to address the underlying technical challenges. Through ex-
periments on real-life event logs the applicability and effectiveness of the
proposed method are evaluated.
Keywords: Process mining ·Organizational mining ·Organizational
model mining ·Overlapping clustering
1 Introduction
Process mining enables data-driven process analysis using the massive amount of
event log data captured by information systems in today’s organizations. Various
techniques have been developed to help extract insights about the actual business
processes with the ultimate goal to improve process performance as well as the
organizations’ business performance. While the main focus of process mining
is on the control-flow perspective, recent years have seen research devoted to
mining other aspects such as the organizational context of business processes.
Organizational mining focuses on discovering organizational knowledge, in-
cluding e.g. organizational structures and human resources relevant to the per-
formance of a business process, from event log data [1]. In any organization
where humans play a dominant role, organizational mining helps managers gain
a better understanding of the de facto grouping of human resources and their
interactions thus to improve the related business processes. The importance of
such organizational knowledge in process improvement is also emphasized by
the fact that 10 of the 29 best practices in process redesign proposed in [2] are
concerned with the structure and population (i.e. resources) of an organization.
Hence, an interesting research topic concerns the discovery of organizational
models from event log data. Given the fact that in many real-life event logs,
only limited information about process execution is provided, it is challenging
to derive the actual organizational model (e.g. an organizational chart) in an
organization. However, it is possible to recognize groups of resources that have
similar characteristics relevant to the performance of a business process. For
example, in [1] the authors propose a resource grouping mechanism based on
how frequently the human resources carry out the same tasks, and suggest that
the discovered organizational groups can be relevant to roles and functional units
in which employees possess similar skills and knowledge to perform the tasks.
To date there have been a number of research efforts on mining organiza-
tional models from event logs (e.g. [1, 3, 4]), whereas almost all of these existing
studies have made an assumption of disjoint organizational groups, which means
that each resource is a member of a single organizational group. In fact, in many
real-world organizations it is common to have employees who possess multiple
skills to share roles and responsibilities across organizational groups. More gen-
erally, modern organizations emphasize the importance of having smooth and
active communication among various functional units, and achieve so by setting
up cross-department roles to enhance the coordination [5]. From the viewpoint
of organizational structures, resources working across different organizational
groups form the overlap between the groups. From the viewpoint of process im-
provement, such resources are likely to be the so-called generalists – a special
category of resources that can help increase the flexibility of a business pro-
cess [2]. In terms of flexibility, we consider the generalists to carry out a role
similar to the role of “libero” in certain team sports.
In this paper we propose an approach for the discovery of organizational
models from event logs, which allows the sharing of human resources between
different organizational groups. By relaxing the assumption of disjoint organiza-
tional groups (applied in most of the existing work), new discovery algorithms
are developed to address the challenges arising from dealing with the potential
overlaps between organizational groups. Based on the characteristics of the prob-
lem of interest, a couple of existing cluster analysis techniques (from the field of
data mining) are chosen and applied in our discovery algorithms. Experiments
are conducted on an implementation of the discovery algorithms, using real-life
event logs, to evaluate the applicability and effectiveness of our approach.
The contribution of our work is twofold. On the one hand, the discovered
organizational model with potential overlaps is a better reflection of the actual
organizational grouping of resources relevant to process execution, and hence it
will enable more insightful resource performance analysis. On the other hand,
identifying resources that belong to more than one organizational group from
event logs presents a novel data-driven approach to the discovery of generalists in
an organization and their organizational positioning (i.e. in which organizational
groups they perform in practice). Finding the information about generalists will
help improve resource utilization and also serve as an important step for action-
able process improvement. For example, one strategy for process improvement
is to keep such resources free when possible, which guarantees flexibility in the
distribution of work [6].
The rest of the paper is organized as follows. Sect. 2 provides a review of the
related work on the topic. Sect. 3 introduces basic concepts and preliminary no-
tions. In Sect. 4, we present our approach for mining organizational models with
overlaps, and in Sect. 5 we discuss the experiments and analyze the evaluation
results. Finally, Sect. 6 concludes the paper and outlines future work.
2 Related Work
The research considering the organizational perspective of process mining origi-
nates from the work by van der Aalst et al. [7], in which several types of inter-
resource relationship metrics are defined for deriving resource social networks
from event logs. Based on the analysis of resource social networks, Song and van
der Aalst [1] propose the conceptual framework of organizational mining as a
sub-field of process mining, within which three research dimensions of organiza-
tional mining are proposed: discovery,conformance checking and extension.
Discovery refers to constructing models that reflect the reality. In the con-
text of organizational mining, these models include organizational models, social
networks and resource assignment/allocation rules. Organizational model min-
ing focuses on finding the grouping of resources (employees), e.g. who belongs
to which functional unit [1, 8], who plays what roles [3, 9] or holds what social
positions in collaboration [10]. Recently, the work of Appice [8] introduces an
approach for mining organizational models using a community detection tech-
nique, which makes no assumption about each resource belonging to a single
group. To the best of our knowledge, this is so far the only existing approach
capable of deriving organizational models with potential overlaps.
The discovery of social networks emphasizes the use of social network analysis
to help understand the structure of communication between individual resources
as well as between organizational groups [4,7, 11]. The research presented in [12,
13] studies the discovery of rules related to staff assignment (who is allowed to
do which tasks) and runtime activity distribution (to whom a specific task is
allocated) to help with diagnosis and optimization of pre-defined rules.
In addition, there is also existing research concerning the organizational per-
spective of business processes at the level of individual resources. For example,
in [14] the authors analyze the correlation between the workload of individual
resources and their performance, and in [15] the authors propose a framework for
analyzing and evaluating different resource behaviors in order to provide insights
towards more informed resource-related decisions for performance improvement.
3 Preliminaries
Here we present several preliminary concepts necessary for describing the prob-
lem, following the conceptual framework of organizational mining defined by
Song and van der Aalst [1]. A typical event log usually consists of a set of
uniquely identifiable cases corresponding to the instances of an underlying busi-
ness process. Each case contains a sequence of events that describe the activities
carried out by some resources. Table 1 gives an example fragment of an event log
recorded by a process-aware information system. Each row refers to one single
event, which is described using attributes such as activity label, timestamp, and
identity of the originating resource1.
Table 1. An example fragment of an event log.
Case ID Event ID Activity label Resource Timestamp
c1e1Register request John 2018/01/03 10:59:06
c1e2Examine thoroughly Mike 2018/02/03 11:10:13
c1e3Decide Clare 2018/02/21 15:43:32
c1e4Reject request John 2018/02/22 10:35:52
Definition 1 (Event Log [7]). Let Tbe a set of tasks and Rbe a set of
resources. E⊆T×Ris the set of events that denote the execution of tasks by
originator resources. For any event e∈E,πt(e)∈Tis the task being executed
(or the activity) in eand πr(e)∈Ris the originator resource of e.C=E∗is
the set of possible event sequences (traces describing a case). L=B(C)is an
event log, where B(C)is the set of all bags (multi-sets) over C.
In Definition 1 we do not take into account the ordering of events in a case.
We focus on two standard attributes of an event – task and resource identity. We
use them to build a simple “profile” for each resource, which reflects the history
of the resource performing activities. Accordingly, a performer by activity matrix
can be used to represent the profiles of a set of resources given an event log.
Definition 2 (Performer by Activity Matrix, adapted from [7]). Given
an event log L, let {e1, ..., en}be the set of all possible events recorded in L.
The performer by activity matrix is an integer-valued matrix Xof size |R| × |T|,
in which each row vector corresponds to the execution history of activities for
a specific resource. Each element of Xdenotes the count of frequencies of a
resource ri∈Rconducting a specific task tj∈T, defined as:
Xij =Σ16k6n(1,if πr(ek) = riand πt(ek) = tj
0,otherwise
where 16i6|R|and 16j6|T|.
1For illustration purposes, resource name is used in the example in Table 1.
Simply consider the example fragment of an event log shown in Table 1.
The performer by activity matrix build from this example based on Definition 2
is shown in Table 2. Below, we propose a generic and simple definition of an
organizational group as a non-empty group of human resources (i.e. employees) in
an organization. For each organizational group, we define a membership indicator
associated with each resource to specify whether or not the resource belongs to
the group.
Definition 3 (Organizational Group). Let Rbe a set of (human) resources
in an organization, an organizational group can be defined as G⊆Rand G6=∅.
Given an organizational group G, for any r∈R, we define a membership indi-
cator function IG:R→ {0,1}where IG(r) = 1 if r∈Gand 0otherwise.
Finally, we define the concept of organization model. It is simply considered
as one entire group of several organizational groups defined in the above.
Definition 4 (Organizational Model). An organizational model Ois a set
that consists of a finite number of (k)organizational groups {G1, . . . , Gk}. For
any resource rthat is part of the organizational model O,rbelongs to one or more
than one organizational group in O. That is, ∀r∈SG∈OG,PG∈OIG(r)>1.
As mentioned before, most of the existing studies in organizational mining apply
the assumption of disjoint organizational groups in an organization, and hence
they require that each resource should only belong to a single organizational
group (i.e. ∀r∈SG∈OG,PG∈OIG(r) = 1). In Definition 4, our focus is to
relax such assumption by recognizing that resources may belong to more than
one organizational group in reality and thus to allow potential overlaps between
different organizational groups.
4 Approach
Organizational model mining aims at recognizing groups of resources having
similar characteristics. We concern the connection between this and the purpose
of cluster analysis in data mining, which is to group a set of data objects into
multiple clusters such that objects within a cluster have high similarity but
are dissimilar to those in other clusters [16]. As a relatively mature field, there
exist various types of techniques developed to provide solutions for different
requirements and contexts. Since our intention is to derive results in which one
resource may be member of more than a single organizational group, we select the
technique of overlapping clustering, which allows flexible assignment of one data
object to multiple clusters. In this paper, we design an approach adopting the
idea of overlapping clustering to solve the problem of discovering organizational
model with overlaps. Fig. 1 gives an overview of the three-phased procedure.
We start from constructing the performer by activity matrix that characterizes
the resources. Then we transfer the problem into cluster analysis and apply the
selected model and algorithm to produce the clustering result, from which we
derive an organizational model as the end result.
1. Perform er-Activity matrix
2. Similarity measure
event
log
organizationa l
model
Characterize
Resources
Run
Cluster
Analysis
Determine
Resource
Membership
Clustering
result
Fig. 1. The designed procedure for discovering organizational model with overlaps.
4.1 Characterizing Resources
Given an event log, we construct the performer by activity matrix by directly
following Definition 2 and determine the execution frequencies while iterating
over the events. Table 2 shows the result of deriving the matrix using the example
event log fragment in Table 1 as input.
Table 2. The performer by activity matrix built from the example event log fragment.
Activity 1 Activity 2 Activity 3 Activity 4
Register request Examine thoroughly Decide Reject request
John 1 0 0 1
Mike 0 1 0 0
Clare 0 0 1 0
Once the performer by activity matrix has been built, we need to select a
measure for quantifying the similarity between any two resources by comparing
the corresponding row vectors, in order to further group similar resources and
derive an organizational model. Some variants of distance-based metrics pro-
vide meaningful measures in a process mining context. The Hamming distance,
for example, accounts for whether or not two resources have executed the same
types of tasks. Meanwhile, correlation-based metrics such as Pearson’s correla-
tion coefficient provide a view of statistical correlation. The choice of similarity
measure should be done depending on the purpose and context of analysis.
For the next step, we apply the clustering techniques in order to obtain the
clusters of resources. Two possible solutions are presented then. Since these two
vary in terms of the deciding the final clusters, we will describe how to derive
the end result, i.e. the output organizational model, respectively.
4.2 Solution 1: Cluster Analysis using a Mixture Model
We first elaborate on how to correlate the current problem with the concepts
of overlapping clustering. The concept of probabilistic cluster and the hypoth-
esis of mixture models are commonly used in cluster analysis to characterize
the flexible assignment of one object to multiple clusters simultaneously. The
hypothesis states that the latent categories hidden in the data objects could be
mathematically represented using a series of distribution functions [16]. Each
data object is related to each latent category by a sampling probability, and is
viewed as a sample drawn from a mixture of distributions. In the context of our
problem, we can regard the execution history of activities (i.e. the row vector in
the performer by activity matrix corresponding to a resource) as the result of a
resource following the work patterns of the organizational group(s) it belongs to.
If the resource is indeed a member of several different groups, then its execution
history of activities should be the consequence of multiple work patterns. We
may therefore adopt the hypothesis of mixture models as an idea for a solution.
First, cluster the resources by leveraging the performer by activity matrix along
with the specified similarity measure and find the distribution function for each
cluster, then for each row vector we calculate a sampling probability related with
each cluster, which could be used to decide the membership of the resource.
Following the idea we could apply a classic Gaussian mixture model (GMM)
as the first solution. In GMM we assume a Gaussian distribution for each latent
category, and apply the well-founded EM algorithm [16] to fit the mixture model
using the performer by activity matrix. EM works in an iterative fitting process,
which starts with a random initialization and updates the mixture model greed-
ily towards a higher value of the goal function (the likelihood of sampling all
the vectors using the current model). The mixture model converges as the goal
function value no longer increases or updates by a very trivial scale.
Using the converged mixture model, we can calculate the posterior probabil-
ity of a row vector relating with each cluster, and take the result as the sampling
probability. However, for actually deciding the membership of a resource, we need
to choose a threshold to be applied on the probability value, which determines if
the resource belongs to one or several of the groups. For example, if the chosen
threshold value is 0.5, then the resource should belong to a group only if its
related sampling probability is larger or equal to 0.5.
For the basic solution using GMM, we notice some problems related to its
configuration. Before starting the fitting process, it requires us to decide the
number of clusters upfront. This should be done based on the control of granu-
larity we desire: with a higher number it enables us to discover more fine-grained
groups, which may be the very specific roles or small workgroups, whereas a
lower number of clusters would possibly lead to finding departments at a higher
level. Another problem concerns the thresholding step applied for the purpose
of deciding resource membership. It is hard to determine an effective level of
probability value that decides whether a resource indeed belongs to an organi-
zational group or not: for instance, for a fitted GMM we could calculate the
result that an involved employee Jack has the probability value of 0.49 that he
belongs to Group 1, and 0.51 that he belongs to Group 2. The question is: how
should we actually decide Jack’s membership given these numbers? Selecting an
appropriate threshold value may become a challenging task, since the scale of the
estimated posterior probabilities lack a solid interpretation in the context of or-
ganizational model mining. We therefore present another overlapping clustering
algorithm that addresses the challenge.
4.3 Solution 2: Cluster Analysis using a More Generative Model
Consider the example of deciding Jack’s membership illustrated before. The use
of mixture models like GMM poses the challenge of configuring proper threshold
parameter, which may hinder us from directly applying the method for discover-
ing organizational models. The challenge arises from the underlying hypothesis
of mixture models: when we view the row vector corresponding to a resource as
a data object being clustered, the posterior probabilities that we use for later
deriving membership only indicate the possibilities of having the current data
object sampled from each of the distributions independently [16]. Hence a mix-
ture model may fail in well characterizing the reality that, for resources with
multiple memberships across several groups, their execution history of activities
results from the joint effect of all the work patterns of the groups.
Without shifting from the general concepts of both organizational model
mining and overlapping clustering, we seek to find a more natural and descriptive
model that avoids deriving membership from probabilities, and constitutes a
better solution for the current problem.
The Model-based Overlapping Clustering (MOC) model [17] bases itself on
the same concepts of probabilistic clusters as GMM does, but without employ-
ing the hypothesis of having objects sampled from a mixture of distributions
related with the latent categories. Instead, a boolean-valued membership vector
is defined directly for each of the objects to be clustered, of which the values
are inferred after fitting the model with the data. In comparison with mixture
models, the MOC model is a more natural generative model for overlapping clus-
tering. In MOC the data objects being clustered are hypothesized to be generated
by simultaneously considering multiple components, as each of the components
refers to a part of the model that relates to one of the latent categories to be
discovered (similar to the distribution functions).
Algorithm 1 depicts the procedure of applying the MOC model to the current
problem. We omit some of the mathematical details here for brevity, for which
one may refer to [17] for a more in-depth explanation. Given nresources and
the related event log, we assume that the performer by activity matrix Xand
similarity measure have been decided prior to running the algorithm, and the
granularity of analysis has been specified already, i. e. kgroups to be discovered.
The algorithm starts by an initial estimate of the membership matrix M, which
is usually initialized in a random manner. Another model parameter to be ini-
tialized is a matrix that represents the active status of each component in the
MOC model, denoted as A, for which random initialization will be fine.
After the initialization of the model parameters we proceed to the iterative
process for fitting the model to the data (Line 3-10). At each iteration we first
update the value of Adirectly using the current Mand X[17]. In the next step,
for each membership vector Miwe try to find a value that maximizes the metric
value. The search may be time-consuming when the desired group number k
is large, however certain algorithms could be plugged in here to speed up the
search process [17]. When the appropriate setting of Mhas been obtained, we
calculate the value of the goal function defined here as the log-likelihood (Line 7),
and compute the increase in comparison to the result of the last iteration. The
iterative updating process stops when convergence is reached, i.e. the increase
in the goal function value is sufficiently small.
Algorithm 1: Applying MOC for Discovering an Organizational Model
Input:
–{r1,...,rn}: the nresources involved;
–X: the constructed performer by activity matrix, also assuming that the
similarity measure has been specified accordingly;
–k: the number of organizational groups expected to be discovered
(depending on the desired granularity).
Output: O: the resulting organizational model consisting of kgroups.
// Step 1: Initialize the membership parameter
1Initialize an n×kboolean value matrix M, where each of the nrow vectors
indicates the membership of a corresponding resource
2Initialize ak×dreal value matrix Athat denotes the active status of each
component in the model
// Step 2: Fit the model to the data through iterative updating
until convergence
3repeat
// Update Aby direct computing the value from Xand M
(cf. [17])
4A←update (A, X, M )
// Update Mby searching a setting that maximizes the selected
similarity measure
5for i= 1 to ndo
6Mi←argmax
Mi∈{0,1}k
SIMILARITY MEASURE (Xi, MiA)
7end
// Calculate the goal function value using the log-likelihood
(cf. [17])
8L= log P(X, M , A)
9Calculate the increase ∆L by comparing with the last iteration
10 until ∆L is sufficiently small
// Step 3: Derive the resulting organizational model utilizing the
membership matrix
11 Initialize kempty sets G1, G2,...,Gk
12 for i= 1 to ndo
13 for j= 1 to kdo
14 if Mij =true then
15 Gj←Gj∪ {ri}
16 end
17 end
18 end
19 return O={G1, G2,...,Gk}
With the fitted model we can now derive the end result in a straightforward
way, since the membership of all the nresources has been determined as the
value of the n×kmembership matrix M. Therefore, we just need to simply
assign the resources to the corresponding ones of the ksets (Line 11-18), and
return the resulting sets as the discovered organizational groups.
Comparing to the more na¨ıve solution of GMM, the solution using MOC
model avoids introducing probabilities as the degree of resource membership,
and therefore addresses the challenge of having to select thresholds. Given the
event log and resources to be analyzed, users would only need to focus on the
resource profiling phase, and then set up the expected number of groups. The
end result will be an organizational model containing the exact number of groups
as required, where overlaps are allowed to exist.
5 Evaluation
5.1 Experiment Design
Both solutions (applying either GMM or MOC) have been implemented in a
standalone demo1. We evaluated their feasibility on real-life event log data. We
aim at giving empirical validation on whether the proposed solutions work ef-
fectively in discovering organizational models when there indeed exist overlaps
among organizational groups.
Event Logs. Different from the evaluation methods in the previous research on
the problem (cf. [1], [8], [11]), the purpose of the validation here requires us to
be aware of the “ground truth” information relevant to the internal groups in an
organization a priori. For this purpose we picked two sets of real-life event logs,
namely “WABO” and “Volvo”. The background of these event log datasets are
as follows:
–WABO: The event log from the WABO dataset contains the records of the
receiving phase of an environmental permit application process in an anony-
mous municipality within the CoSeLoG project [18].
–Volvo: This dataset includes event logs generated from the problem man-
agement system VINST of Volvo Belgium, which was originally released for
the BPI Challenge 2013 [19]. It contains the event logs that describe several
business processes handling incidents and problems in the IT-services deliv-
ered and/or operated by Volvo IT. We choose the event log related with the
process managing the open problems for experiment use.
The event logs are recorded in the IEEE standard XES format [20], and in-
clude an extended event attribute termed org:group, which indicates the group
identity of the resource that triggered the event. We recognize that the ground
truth organizational models can be extracted by utilizing this information of
identities, which can then serve as the reference models for our experiments.
To do this we first filter out the events with missing values on org:group (in-
cluding both null and invalid ones). Then we extract the ground truth organi-
zational model by putting resources together into groups accordingly, based on
the org:group values they relate to as event originators. Table 3 gives a brief
1https://github.com/royyjing/bpm-2018-Yang Find
overview of the preprocessed event logs, along with some basic statistics of the
extracted reference models: the average size of groups (Avg. group size), and the
average number of groups that a resource belongs to (Avg. membership). One
may recognize immediately the existence of overlaps in the reference models af-
ter inspecting the basic statistics shown in the table. A further comparison on
Avg. membership reveals that the overlapping condition is less obvious in the
Volvo case (Avg. membership 1.176 while WABO has a value of 3.886), suggest-
ing considerably fewer employee resources possessing multiple group identities
in Volvo IT.
Table 3. Overview of the event logs and the extracted reference models.
Event log Cases Events Activities Resources Organizational Avg. Avg.
groups group size membership
WABO 1,348 6,641 27 44 9 19.0 3.886
Volvo 818 2,331 5 239 11 25.5 1.176
Experiment Setups. We conducted the experiments using the comprison
method. Two methods proposed in previous research are selected as baseline:
a traditional partitioning method that produces disjoint organizational mod-
els [1], namely MJA; and a community detection based method developed by
Appice [8] that is capable of deriving organizational models with possible over-
laps, namely Commu. We examine if the organizational models discovered from
the same source of event logs using GMM and MOC can better capture the
reality, i.e. more similar to the reference models.
To start with, we build the performer by activity matrix, and choose the
Pearson’s correlation coefficient as the metric for similarity measure. Since the
setup of the algorithms involved in evaluation may vary, we decided to configure
the parameters for each algorithm separately, as long as they produce resulting
organizational models with exactly the same number of organizational groups
discovered as that in the reference ground truth.
Evaluation Metrics. For the purpose of comparing between the results of dis-
covery and the reference models to assess the effectiveness of different methods,
we consider adopting extrinsic evaluation metrics. One example is the entropy
measure [1], which can be used for measuring the scale of difference between a
generated model and the referenced one. However, as the current research has
been extended to the overlapping situation, the entropy measure becomes inap-
propriate as well as many other commonly used extrinsic measures. We therefore
turn to the extended BCubed metrics (including BCubed Precision, Recall and
F-measure) [21], as they are applicable for evaluation on the overlapping cases.
From an organizational model mining point of view, the meaning of the BCubed
metrics can be interpreted as follows:
1. BCubed Precision represents the ratio of how many resources in a same dis-
covered organizational groups belong to the same actual groups. A higher
value of BCubed Precision means fewer mistaken assignments in the discov-
ered organizational model.
2. BCubed Recall represents the ratio of how many resources from a same
actual groups are assigned to the same discovered organizational groups. A
higher value of BCubed Recall means more resources with the same actual
group identities are placed together by the mining algorithm.
3. BCubed F-measure is a combination of BCubed Precision and Recall, defined
as the harmonic average of the two.
Besides the BCubed metrics, we also want to compare the basic statistics
of the discovered organizational model (Avg. group size and Avg. membership),
with those of the groundtruth model.
5.2 Comparing with the Disjoint Partitioning Method
In the first experiment we wish to compare our solutions with the disjoint parti-
tioning method MJA. The idea behind MJA is to view the resources as vertices
in a graph, and connect weighted edges between them based on the measured
similarity values. By eliminating certain edges by a threshold value, the origi-
nal graph is further partitioned into several connected components, which are
taken as organizational groups that constitute the final organizational model.
The result generated from MJA is obviously disjoint.
Table 4 shows the evaluation results measured by the BCubed metrics. From
the table we can see that MJA obtains higher precision rates. However, the dis-
joint nature of MJA prevents it from recognizing the fact that similar resources
may possibly share more than one group identities in an overlapping organiza-
tional model. Thus, for MJA, similar resources are clustered into one group only,
which lead to the relatively lower recall.
On the other hand, the proposed solutions using either GMM or MOC have
comparatively lower precision yet higher recall values. It can be explained that
both overlapping clustering based algorithms tend to put more resources into the
groups, which is consistent with the larger group sizes shown in Table 5. This
leads to the better recall rates, but at the same time makes the discovered orga-
nizational groups contain relatively members being mistakenly assigned, which
directly cause the lower precision of GMM and MOC.
Moreover, for the Volvo case we notice that even the baseline MJA produces
a relatively lower precision, and the situation of recall rates mentioned above
becomes even more significant. The reason is due to the large total number of
resources compared to the much smaller number of activity types (239 resources
compared to 5 activity types). The smaller number of activity types leads to
fewer columns in the performer by activity matrix, and may therefore weaken
the effect of measuring similarity.
Despite the observation that GMM and MOC may tend to sacrifice some
precision rate and bring mistaken assignments, from Table 5 we can draw a
conclusion – the overlapping-clustering-based solutions are able to derive an
overlapping organizational model that captures the reality, whereas methods
like MJA holding the assumption of disjoint organizational model are not.
Nevertheless, we still have the following questions: How effective are our
solutions comparing to other solutions that can also produce overlapping or-
ganizational models? Will the other solutions also encounter the problem of
unsatisfying precision? We will explore the answers to these questions through
the following experiment and analysis.
Table 4. Results of comparing with MJA on the BCubed metrics.
Event log BCubed Precision BCubed Recall BCubed F-measure
MJA GMM MOC MJA GMM MOC MJA GMM MOC
WABO 0.814 0.624 0.757 0.213 0.812 0.735 0.337 0.706 0.745
Volvo 0.496 0.186 0.24 0.397 0.944 0.94 0.441 0.31 0.382
Table 5. Results of comparing with MJA on the grouping statistics.
Event Log Avg. group size Avg. number of membership
Ground truth MJA GMM MOC Ground truth MJA GMM MOC
WABO 19.0 4.9 28.4 22.8 3.886 15.818 4.659
Volvo 25.5 21.7 146.5 110.9 1.176 16.745 5.105
5.3 Comparing with the Community-Detection Based Method
In this experiment we choose as baseline a community detection based ap-
proach [8] which we refer to as Commu. Our goal is to make a comparison
between the effectiveness of Commu and our approach. Commu is based on
social network analysis techniques rather than cluster analysis, but shares the
same purpose of grouping cohesive resources into communities that represent
the internal organizational groups. It applies the linear network model with the
Louvain algorithm, and derives organizational models which allow the existence
of overlapping communities (organizational groups).
Tables 6 and 7 show the evaluation results of this experiment. By observing
the average number of membership we first confirm that the baseline method
Commu indeed generates overlapping results. For the BCubed metrics, we no-
tice that GMM performs roughly the same as Commu, whereas MOC performs
better than Commu in both cases. And the grouping statistics show that the
models produced by using either GMM or MOC are more realistic compared
with Commu.
Meanwhile, we learn from the tables that Commu also produced a result of
low precision and oversize groups, as in the Volvo case, and even worse while
comparing with GMM and MOC (refer to the grouping statistics in Table 7).
In general, we may conclude that our approach is more effective as a solution
to discovering organizational models with overlaps, compared to the community
detection based method. Nevertheless, as both methods have the shortcoming
of introducing mistaken assignment of resources to groups causing low precision
and unrealistic group sizes, further work is needed to address this shortcoming.
Table 6. Results of comparing with Commu on the BCubed metrics.
Event log BCubed Precision BCubed Recall BCubed F-measure
Commu GMM MOC Commu GMM MOC Commu GMM MOC
WABO 0.718 0.624 0.757 0.651 0.812 0.735 0.683 0.706 0.745
Volvo 0.195 0.186 0.24 0.948 0.944 0.94 0.324 0.31 0.382
Table 7. Results of comparing with Commu on the grouping statistics.
Event Log Avg. group size Avg. number of membership
Groundtruth Commu GMM MOC Groundtruth Commu GMM MOC
WABO 19.0 28.8 28.4 22.8 3.886 5.886 5.818 4.659
Volvo 25.5 152.6 146.5 110.9 1.176 7.025 6.745 5.105
5.4 Discussion
We can draw some interesting insights considering results from both experiments
conducted. The first conclusion concerns the comparison of effectiveness between
GMM and MOC. It has been evaluated through the experiments that MOC
performs better, indicated by the higher precision and F-measure, along with the
grouping characteristics being more similar to the ground truth model. Taking
into consideration that it requires no cumbersome decision to set up the extra
threshold parameter when applying MOC, we conclude that MOC will serve as a
better solution than GMM for discovering organizational models with overlaps.
On the other hand, we also realize that for our solution, there exists a short-
coming which would become significant when the latent organizational model
is less overlapped. We infer the possible reasons behind it as twofold. The first
one concerns the relatively fewer types of activities compared to the number of
resources. The second concerns the lack of constraints on the number of groups
allowed for each resource to be assigned to. As the former is limited by the
content of the event log, we discuss the remedy for the latter.
Given no constraints, both GMM and MOC may try to relate resources to
many organizational groups as long as the goal function value is being optimized.
This eventually causes the unrealistic mining result in which one resource is a
member of considerably many organizational groups simultaneously, diverging
from the reality that some resources may possess few or no shared group identi-
ties, as in the Volvo case. To solve this, a natural idea is to set up the constraints
to mitigate the problem of involving too many resources. Yet this would require
more prior knowledge of the underlying organizational structure to implement.
Nevertheless, we argue that such an improvement needs only slight modification
on the current solution. For GMM, it requires the proper threshold value. For
MOC, heuristics are to be introduced to prune the search space in updating the
estimate of membership. Another remedy could be mixing application of the
proposed solution with the traditional disjoint method: Given an organizational
model mining task with the performer by activity matrix has been built along
with the specified similarity measure, one may first mine a disjoint model using
the traditional method, and utilize the obtained model statistics for the guided
initialization of the parameters. Then, apply GMM or MOC to discover an or-
ganizational model with potential overlaps. We plan to leave the exploration for
improvement to our future research on the topic.
6 Conclusion
Organizational model mining techniques enable the discovery of organizational
models from event logs. In this paper, we relax the assumption of disjoint orga-
nizational groups held by existing methods and discover organizational models
in which individual resources may share multiple group identities. We refer to
overlapping clustering techniques and introduce two solutions, GMM and MOC,
for deriving organizational models with overlaps. Results from experiments on
real-life event log data demonstrate the applicability and effectiveness of the
methods. We also recognize the potential limitation of our solution and con-
clude the reasons behind it, which lead to identifying the potential heuristics for
further amending the current approach.
In future work we will consider the following aspects: (1) to improve our
approach by effectively incorporating the identified heuristics; (2) to link the
current research with performance analysis on generalist resources; (3) to con-
duct evaluation on more real-life cases.
Acknowledgments. This work is supported by the National Key Research
and Development Program of China (Grant No. 2017YFB0202200); the National
Natural Science Foundation of China (Grant No. 61572539); the Research Foun-
dation of Science and Technology Plan Project in Guangdong Province (Grant
No. 2016B050502006); and the Research Foundation of Science and Technology
Plan Project in Guangzhou City (Grants No. 2016201604030001, 201704020092).
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