Veröffentlichungen
Im Folgenden finden Sie eine Liste aller wissenschaftlichen Publikationen, Forschungsartikel, Bücher, Dissertationen und Werkstattmaterialien, die aus dem Forschungsprojekt SFB768 hervorgegangen sind.
- Forschungs-artikel
- Dissertationen
- Bücher
- WorkshopMaterial
Zeitschriftenbeiträge

Understanding the Relationship of Conflict and Success in Software Development Projects
Expand Abstract
Context
Software development incorporates numerous people with diverse expertise and expectations. This makes conflict a common phenomenon in software development. Besides human causes, many conflicts in software development root in the tools and processes. Moreover, the growing role of software in any type of system is increasing the heterogeneity in software projects. The number and variety of tools and processes are increasing. Nevertheless, the relationship between conflicts, particularly rooted in non-human elements, and software project success is still unclear.
Objective
We aim to understand the impact of conflict on the success of software development projects for different types of conflict and different environments. Particularly, we distinguish between human-rooted conflict (HRC) and non-human-rooted conflict (NHRC). Moreover, we investigate whether organization size and team size moderate the impact of conflict on software project success.
Methods
First, we conduct a survey and analyze it using structural equation modeling (SEM) to investigate any correlation between conflict and software project success. Second, we explore the reasons behind the relationship between conflict and software project success by conducting 13 semi-structured expert interviews.
Results
HRC is always a threat to software project success for any organization or team size. Based on the interviews, resolving an HRC is regularly problematic. On the other hand, NHRC is negatively correlated with software project success only in corporate organizations and small teams. High coordination overhead and dependency on tools and processes make NHRC more influential in corporate organizations. In contrast, overlooking non-human elements and lack of experienced individuals in smaller teams make them more vulnerable to NHRC.
Conclusion
While the detrimental impact of HRC is constant for software project success, NHRC can be controlled efficiently. Corporate organizations need to frequently improve the non-human elements in the development. Smaller teams should expect tools and processes to be significantly influential in their success.
Autor: Basirati, M. R.; Otasevic, M.; Rajavi, K.; Böhm, M.; Krcmar, H.

Modular change impact analysis in factory systems
Expand Abstract
Shorter product innovation cycles, high variant products, and demand fluctuation, as well as equipment life cycles and technology life cycles force manufacturing companies to regularly change their manufacturing system. In order to address this challenge, an efficient and structured change management is required. As change causes and factory elements are connected via a complex network of relations and flows, an essential step in change management is the evaluation of considered adjustments with regard to their effects on the current production system. Depending on the context of the application, change impact analysis must process specific inputs and deliver different results. Current approaches, however, each focus only on selected aspects of the versatility of change effects. To address this challenge, this paper presents a modular approach for the individual design of change impact analysis.
Autor: Bauer, H.; Haase, P.; Sippl, F.; Ramakrishnan, R.; Schilp, J.; Reinhart, G.

A requirements data model for product service systems
Expand Abstract
Product service systems (PSS) are bundles of physical technological elements and service elements that are integrated to solve customer problems. In practice, most components of PSS are developed independently from each other, which leads to problems with coordination of development activities and integration of PSS components. Therefore, an integrated requirements engineering for PSS is needed that deals with the involvement of developers from product engineering, software engineering, and service engineering, as well as the inherent complexity of the PSS and the development process. In a case study with the development department of a PSS provider, we analyzed requirements documents and conducted expert interviews. We identified problems in the development, for example, that requirements on different levels of abstraction are intermingled, rationales for requirements are missing, and the concretization of requirements is unclear. To solve these problems, we propose a requirements data model (RDMod) for requirements to PSS. An RDMod describes different types of requirements and the relations between them. Thus, it is a scheme for the concretization of the requirements, which especially addresses the problems of structuring the requirements, enabling traceability, and finding conflicts. We then used an analytical evaluation, a feature-based evaluation and a retrospective application with requirements analysts of the industry partner. In a joint workshop, we specified requirements for a PSS with the RDMod. In structured interviews, we analyzed the perceived advantages of the RDMod. The experts confirmed that the RDMod is applicable in their development and it provides a clear structure for the requirements and therefore helps overcoming the identified problems.
Autor: Berkovich, Marina; Leimeister, Jan Marco; Hoffmann, Axel; Krcmar; Helmut

Vernetzung heterogener Akteure in Innovationsnetzwerken
Expand Abstract
In Innovationsprozessen von Produkt-Service-Systemen (PSS) gewinnt die Frage an Bedeutung, wie Organisationen die Zusammenarbeit heterogener Akteure zielgerichtet koordinieren und gestalten können. In diesem Beitrag werden drei Maßnahmenbündel vorgestellt, welche die erfolgreiche Vernetzung und Zusammenarbeit heterogener Akteure in Innovationsprozessen unterstützen: Erstens, Maßnahmen, die Teams und vernetzte Akteure unterstützen, erfolgreich mit der Komplexität und Dynamik von PSS-Innovationen umzugehen und Wissen auszutauschen (Teilprojekt A8); zweitens, Maßnahmen, die Organisationen bei der Entwicklung organisationalen Lernens unterstützen (Teilprojekt A11); drittens, Maßnahmen, die Beziehungen und Abhängigkeiten von Akteuren in Innovationsprozessen offenlegen und grafisch illustrieren (Teilprojekt D2).
Autor: Buchholz, Johan; Drewlani, Tobias; Gammel, Josef H.; Dr. Pantförder, Dorothea; Dr. Reif, Julia; Dr. Kugler, Katharina; Prof. Dr. Brodbeck, Felix

Adjustable and Adaptive Control for an Unstable Mobile Robot Using Imitation Learning with Trajectory Optimization
Expand Abstract
In this contribution, we develop a feedback controller in the form of a parametric function for a mobile inverted pendulum. The control both stabilizes the system and drives it to target positions with target orientations. A design of the controller based only on a cost function is difficult for this task, which is why we choose to train the controller using imitation learning on optimized trajectories. In contrast to popular approaches like policy gradient methods, this approach allows us to shape the behavior of the system by including equality constraints. When transferring the parametric controller from simulation to the real mobile inverted pendulum, the control performance is degraded due to the reality gap. A robust control design can reduce the degradation. However, for the framework of imitation learning on optimized trajectories, methods that explicitly consider robustness do not yet exist to the knowledge of the authors. We tackle this research gap by presenting a method to design a robust controller in the form of a recurrent neural network, to improve the transferability of the trained controller to the real system. As a last step, we make the behavior of the parametric controller adjustable to allow for the fine tuning of the behavior of the real system. We design the controller for our system and show in the application that the recurrent neural network has increased performance compared to a static neural network without robustness considerations.
Autor: Dengler, C. & Lohmann, B.

Diving deep into team adaptation: How does it really unfold over time?
Expand Abstract
Objective: We investigated whether teams adapt to an unexpected event by executing the 4-phase team adaptation process (i.e., situation assessment, plan formulation, plan execution, and team learning) and whether the execution of this 4-phase sequence leads to high team performance, as proposed by Rosen et al. (2011). Method: In a laboratory study, we observed 70 teams of 4 individuals performing a task after an unexpected event. We coded the sequence of team adaptation phases based on team members’ communications and behaviors. For hypothesis testing, we performed a lag sequential analysis to determine whether sequences of team adaptation phases occurred (1) more often than other sequences and (2) more often in high- versus low-performing teams. Results: Theoretically predicted phase sequences did not occur more often than other phase sequences, except for the 2-phase sequence situation assessment followed by plan execution. Instead, teams performed “forward–backward” sequences between plan formulation and plan execution and between plan formulation and situation assessment. Theoretically proposed sequences were less frequent in high- versus low-performing teams, whereas other phase sequences not proposed by theory were more frequent in high-performing teams. This suggests that high-performing teams were more flexible in their sequencing of team adaptation phases. Conclusions: Our research suggests more flexible sequences of team adaptation phases than proposed by theory and thus draws a nuanced picture of the complex nature of the team adaptation process. To fully capture the team adaptation process, we suggest incorporating forward–backward phase sequences into team adaptation theory.
Autor: Georganta, E., Kugler, K. G., Reif, J. A., & Brodbeck, F. C.

The four-phase team adaptation process: a first empirical investigation.
Expand Abstract
Purpose
Several theoretical models have been developed to describe the process of successful team adaptation. Testing the models through empirical research is lacking. This study aims to empirically examine the way teams adapt to unexpected or novel circumstances and investigate the four-phase team adaptation process (i.e. situation assessment → plan formulation → plan execution → team learning), as proposed by Rosen et al. (2011).
Design/methodology/approach
To test the positive relationship between the four team adaptation phases and their suggested sequence, a cross-sectional field study was conducted. Data were collected from 23 teams participating during an 8-week team project.
Findings
Results from random intercept models confirmed that the team adaptation process consisted of four phases that were positively related to each other. As expected, plan formulation mediated the positive relationship between situation assessment and plan execution. However, team learning was independently related to all three previous phases, and not only to situation assessment as theory suggests.
Originality/value
To the best of the authors’ knowledge, the present study is one of the first attempts to test the theoretical model of the team adaptation process presented by Rosen et al. (2011). Findings illustrated that the team adaptation process is not a simple four-phase sequence, but it constitutes four dynamic phases that are strongly interrelated to each other.
Autor: Georganta, E., Kugler, K. G., Reif, J. A., & Brodbeck, F. C.

Technology lifecycle-oriented search for production technologies
Expand Abstract
The adoption of production technologies is a major challenge for manufacturing companies. Despite the long term impact of decisions on production technologies, companies are often unaware how to search for alternative production technologies. We developed a method that focusses on the systematic search for production technologies for fulfilling future manufacturing tasks. The method consists of three steps including the selection of information sources, information search and information evaluation. It takes advantages of the concept of technology lifecycles. The method provides a useful tool for producing companies and has been applied exemplary in the automotive industry.
Autor: Greitemann, Josef; Zaggl, Michael A.; Hehl, Martin; Raasch, Christina; Reinhart, Gunther

Current challenges for sustainable product development in the German automotive sector: A survey based status assessment
Expand Abstract
Since 2015/16, dieselgate has initiated transformations of the automotive industry towards the integration of sustainability into the product development process. The present study combines a qualitative approach, based on semi-structured expert interviews, with a quantitative online survey to identify the current status of this implementation. The objective of the paper is to provide an overview on how German automotive companies currently deal with challenges and chances of a sustainable product development. The study obtained the following core conclusions: (1) A common understanding of the term sustainability is missing and a company-wide definition would be beneficial. (2) There is no consensus on the optimal organizational embedment for sustainability into a company. A centralized responsibility plus distributed awareness was identified as the most promising solution. (3) As a matter of supply and demand, automotive companies will not over-satisfy the customers’ demand. As dieselgate has boosted public interest, possible competitive advantages were identified by transforming the product property “sustainability” to a unique selling point. (4) There is an unmanageable amount of methods for the implementation of sustainability in the product development process. For that reason, academically developed methods are only rarely used in industry. (5) Companies are retrospectively evaluating the results of the development rather than using assessment outcomes systematically to improve the product prospectively. (6) Major potential drivers for sustainable product development are laws & politics, customers and competition. Sustainability could become more attractive for industry and customers by creating win-win-solutions. Conceivable propositions are tax advantages or Pigovian taxes, the internalization of sustainability, the shift from tank-to-wheel- towards holistic well-to-wheel-analyses or product service-systems.
Autor: Held, Maximilian; Weidmann, Dominik; Kammerl, Daniel; Hollauer, Christoph; Mörtl, Markus; Omer, Mayada; Lindemann, Udo

A hierarchical taxonomy of business model patterns
Expand Abstract
Although business model innovation (BMI) is essential to remaining competitive, many firms fail at it. A promising approach is building on reoccurring successful solutions – business model patterns (BMP) – as a blueprint for BMI. However, existing patterns face constraints subject to a high diversity and overlaps among patterns. In addition, literature do not consider relations among BMPs, which limits their potential for BMI. This paper develops a hierarchical taxonomy of BMPs including generalizations and specializations based on inheritance. We conduct a literature review to identify patterns and a cluster analysis to create an inductive structure, followed by a qualitative analysis. The resulting hierarchical taxonomy includes 194 elements. It is the first hierarchical taxonomy of BMPs. The hierarchy addresses the diversity of patterns and overlaps with inheritance. It aids research to structure and understand BMPs. For practice, the taxonomy allows for the application of patterns and supports BMI.
Autor: Hermes, Weking, Jörg; Hein, Andreas; Böhm, Markus; Krcmar, Helmut

When to Signal? Contingencies for Career-Motivated Contributions in Online Collaboration Communities
Expand Abstract
Online collaboration communities increasingly take new roles besides knowledge creation and exchange, especially the role as a skill-signaling channel for career-motivated community members. This paper examines the contingency effects of job-market conditions for career-motivated knowledge contributions in online
collaboration communities. From the data of individual-level activities in a computer programming-related online Q&A community (Stack Overflow), merged
with job-market data for software developers, we find robust evidence of a positive association between community members’ career motivation and their knowledge contributions. More importantly, we find that this positive relationship is strengthened by job-market conditions: the number of vacancies in the job market, the expected salaries from these jobs, and the transparency in the flow of career-related information between the community and external recruiters. We contribute to the motivation literature in online collaboration communities by identifying and
substantiating the role of contextual factors in mobilizing members’ career motivation. Our study thus offers novel insight into how career motivation can be effectively utilized to motivate contributors in these communities. Our findings also point to a possible paradigm change by characterizing online collaboration communities as emerging institutions for career motivation and skill signaling.
Autor: Lee, Jeongsik; Park, Hyunwoo; Zaggl, Michael

How Open Crowds Self Organize
Expand Abstract
The ability of open crowds to produce useful and novel solutions is of significant research and practical interest. Much of the existing research has assumed that crowd participants approach problem-solving autonomously and independently of one another. In the Stack Exchange network, we explored problems posted by open crowds and the sequences of suggestions and comments leading up to a solution that was novel and judged by the solution seeker as useful for solving the problem. In the sequences of suggestions, we found indications of self-organization as the crowd emergently accumulated knowledge in specific patterns that were more likely to lead to accepted solutions. The patterns contained positive and negative forms of feedback ensuring that the crowd would, on its own and without external governance intervention, engage in actions that eventually led to accepted solutions. In total, based on the observed knowledge accumulation patterns, three self-organization principles were derived and incorporated into a theory of self-organization for creative solution generation in open crowds. Our theory development suggests implications for research on open crowds specifically, as well as for research on new organizational forms.
Autor: Majchrzak, A., Malhotra, A., & Zaggl, M.

Collective navigation of a multi-robot system in an unknown environment.
Expand Abstract
The navigation of autonomous, mobile multi-robot systems in changing environments is a challenging problem investigated over the past years. Cooperative, multiple robots are employed for many different tasks to increase the efficiency and success of a mission. However, many of the existing collective path planning approaches do not guarantee a reliable escape in environments with complex, non-convex obstacles without any prior knowledge. In this study, we developed a navigation framework for multi-robot systems in unknown areas that solely exploit the sensing information and shared data among the agents. The key contribution of this paper is the simultaneous, collision-free motion planning for fully autonomous robots in a collective manner. Furthermore, our communication architecture enables the robots to find an appropriate path to a desired, joint target position, despite the limited sensing and communication range.
Autor: Olcay, E.; Schuhmann, F.; Lohmann, B.

An employee-centered perspective on business processes: measuring “healthy business processes” and their relationships with people and performance outcomes
Expand Abstract
Purpose
Traditional approaches to business processes and their management consider the “people dimension” as an antecedent of process performance. The authors complemented this approach by considering employees as process perceivers and thus taking an employee-centered perspective on business processes. The authors investigated dimensions of healthy business processes, that is, processes which, while promoting performance, foster employee well-being.
Design/methodology/approach
Based on a qualitative dataset and two quantitative studies, the authors developed and validated a scale for healthy business processes, interpreted it from a salutogenic perspective and tested relationships with people and performance outcomes.
Findings
The scale comprises four factors reflecting the three dimensions of the salutogenic concept “sense of coherence”: manageability was represented by the factors process tools and process flexibility; comprehensibility was represented by the factor process description; and meaningfulness was represented by the factor management support. The scale and its subscales were significantly related to people and performance outcomes.
Originality/value
The authors propose that health-oriented business process management and performance-oriented business process management are two components of an integrated business process management that favors neither a functionalist, efficiency-oriented approach nor an employee-oriented approach, but takes both approaches and their interaction equally into account in the sense of person-process fit.
Autor: Reif, J.A.M.; Kugler, K.G.; Stockkamp, M.T.; Richter, S.S.; Benning, V.M.; Muschaweck, L.A.; Brodbeck, F.C.

Core, intertwined, and ecosystem-specific clusters in platform ecosystems: analyzing similarities in the digital transformation of the automotive, blockchain, financial, insurance and IIoT industry
Expand Abstract
Digital transformation is continuously changing ecosystems, which also forces established companies to re-evaluate their value proposition. However, only transformations of single ecosystems have been studied. Therefore, this work targets to examine the similarities of digital transformation in five platform ecosystems: automotive, blockchain, financial, insurance, and IIoT. For our analysis, we combine the strengths of conceptual modeling using e3 value with a cluster analysis based on text mining to identify similarities in the respective ecosystems. As a result, we identified 15 clusters. Cluster 01 is the core cluster, containing the roles of organizations from all five ecosystems. Cluster 02–05 are intertwined, as they include roles from at least two ecosystems. Clusters 06–15 are ecosystem-specific that only include roles found in one ecosystem. Scholars and practitioners can use these clusters when analyzing or building a new platform ecosystem, or transforming a traditional ecosystem towards a platform ecosystem.
Autor: Riasanow, T., Jäntgen, L., Hermes, S., Böhm, M., & Krcmar, H.

Cycle management of manufacturing resources: identification and prioritization of investment needs
Expand Abstract
A novel lifecycle framework for managing manufacturing resources within a company is presented to support the timely, systematic identification of technological need for action. In contrast to the established bathtub curve, the equipments’ age, maintenance costs, downtimes, and technical condition are considered quantitatively taking uncertainties into account. The developed methodology therefore comprises contingency analysis and applies a dynamic set of fuzzy rules for classifying the cycle-stage of multiple manufacturing resources. Integrating these functionalities within one holistic framework, this approach far exceeds existing methods for proactively managing the manufacturing resource lifecycle. Cooperating with one of the leading manufacturer of commercial vehicles, a database comprising 221 relevant manufacturing resource datasets was built as a foundation for statistical analysis. Besides offering general recommendations facilitating a proactive management approach, the developed lifecycle model concentrates further activities on elements that show major improvement potential.
Autor: Schönmann, A. ; Dengler, C. ; Intra, C. ; Reinhart, G. ; Lohmann, B.

How to strengthen a culture of innovation by combining values-based and evidence-based innovation management
Expand Abstract
Values-based and evidence-based innovation management both improve a company’s innovation performance. However, there are no systematic studies of how combining values-based and evidence-based innovation management influences the innovation culture in mid-sized B2B companies. In this exploratory case study, we describe how a longitudinal analysis of innovation culture and a values-based initiative were combined in a 7-step approach, which was applied in a global mid-sized B2B manufacturer of drug-delivery systems and pharmaceutical components over a three-year period. The results of the longitudinal innovation culture survey and the analysis of front-end innovation key performance indicators provided insight into the positive impact of new normative company values on the organization’s innovation culture as well as on the effectiveness of the idea generation process. The exploratory case study demonstrates how a customized combination of values-based and evidence-based innovation management elements can systematically strengthen an organization’s innovation culture and the effectiveness of its idea generation process.
Autor: Seiler, M., Cott, A. B., Torres, V. Reif, J. A. M., Kugler, K. G., Gammel, J. H., & Brodbeck, F. C.

A hierarchical taxonomy of business model patterns
Expand Abstract
Although business model innovation (BMI) is essential to remaining competitive, many firms fail at it. A promising approach is building on reoccurring successful solutions – business model patterns (BMP) – as a blueprint for BMI. However, existing patterns face constraints subject to a high diversity and overlaps among patterns. In addition, literature do not consider relations among BMPs, which limits their potential for BMI. This paper develops a hierarchical taxonomy of BMPs including generalizations and specializations based on inheritance. We conduct a literature review to identify patterns and a cluster analysis to create an inductive structure, followed by a qualitative analysis. The resulting hierarchical taxonomy includes 194 elements. It is the first hierarchical taxonomy of BMPs. The hierarchy addresses the diversity of patterns and overlaps with inheritance. It aids research to structure and understand BMPs. For practice, the taxonomy allows for the application of patterns and supports BMI.
Autor: Weking, J., Hein, A., Böhm, M., & Krcmar, H.

Leveraging industry 4.0 – A business model pattern framework
Expand Abstract
Industry 4.0 (I4.0), also known as the fourth industrial revolution, describes the digitalization of manufacturing industries. The transition to I4.0 is crucial for manufacturing firms to sustain competitive advantage and seize new opportunities. Most research has focused on the technological aspects of I4.0 in the form of product and process innovations. Despite I4.0's rising attention from both researchers and practitioners, little research exists about I4.0 business model (BM) innovation, even though BM innovations can be more successful than product or process innovations. To address this research gap, we analyze 32 case studies of I4.0 BM innovators. We develop a taxonomy to characterize I4.0 BMs and derive 13 patterns of I4.0 BMs by applying the taxonomy to the case studies. Three super-patterns are identified: integration, servitization, and expertization. Integration innovates a BM with new processes and integrates parts of the supply chain. New combined products and services are the basis for servitization. Expertization is a hybrid of product- and process-focused BMs, which includes consulting services and multi-sided platforms. This study contributes to research with a framework for describing, analyzing, and classifying BMs for I4.0. The findings deepen the understanding of how I4.0 impacts ecosystem roles, BMs, and service systems. Archetypal patterns show how firms can leverage I4.0 concepts and build a conceptual basis for future research. The taxonomy supports practitioners in evaluating the I4.0-readiness of their existing BM. The patterns additionally illustrate opportunities for becoming an I4.0 firm.
Autor: Weking, J., Stöcker, M., Kowalkiewicz, M., Böhm, M., & Krcmar, H.

Introducing TRAILS: A tool supporting traceability, integration and visualisation of engineering knowledge for product service systems development
Expand Abstract
Developing state of the art product service systems (PSS) requires the intense collaboration of different engineering domains, such as mechanical, software and service engineering. This can be a challenging task, since each engineering domain uses their own specification artefacts, software tools and data formats. However, to be able to seamlessly integrate the various components that constitute a PSS and also being able to provide comprehensive traceability throughout the entire solution life cycle it is essential to have a common representation of engineering data.
To address this issue, we present TRAILS, a novel software tool that joins the heterogeneous artefacts, such as process models, requirements specifications or diagrams of the systems structure. For this purpose, our tool uses a semantic model integration ontology onto which various source formats can be mapped. Overall, our tool provides a wide range of features that supports engineers in ensuring traceability, avoiding system inconsistencies and putting collaborative engineering into practice. Subsequently, we show the practical implementation of our approach using the case study of a bike sharing system and discuss limitations as well as possibilities for future enhancement of TRAILS.
Autor: Wolfenstetter, Thomas; Basirati, Mohammad R.; Böhm, Markus; Krcmar, Helmut

Manipulation of explicit reputation in innovation and knowledge exchange communities: The example of referencing in science
Expand Abstract
This paper investigates the manipulation of reputation in the context of innovation and knowledge exchange communities. Reputation is crucial for overcoming the free-riding problem and enables community members to be rewarded because their contributions to the common good can be measured. However, the concept of reputation can include the notion of manipulation, which we define as the attempt to change one's reputation without contributing to the community. To investigate the topic of reputation manipulation, we build on the concept of reputation-based reward systems and extend it by distinguishing between implicit reputation, which is uncodified, and explicit reputation, which is codified and centrally counted. We argue that the possibilities for manipulation differ between these two distinctions. We investigate reputation manipulation empirically in the context of science, which is built on an explicit reputation-based reward system, and we use the received citations as an indicator for reputation. We distinguish two forms of manipulation—unjustified self-citing and unjustified reciprocal citing—and find evidence of both within a bibliometric dataset. This paper contributes to the design of knowledge exchange communities by highlighting the opportunities and challenges arising from explicit reputation-based reward systems, specifically the opportunities for manipulation. It also contributes to the work on misconduct in science.
Autor: Zaggl, Michael A.

Do small funding amounts lead to reverse herding? A field experiment in reward-based crowdfunding
Expand Abstract
Several biases are known to influence funding decisions in crowdfunding. Among these biases is herding behavior; that is, the tendency to imitate the funding decisions of others. Herding is a very robust phenomenon in crowdfunding and uniformly characterized as a positive reinforcement effect. We challenge this characterization and ask whether the funding decisions of others may in fact have a negative effect and lead to a reduction of follow-up funding decisions if they are very small – a phenomenon to which we refer as reverse herding. We conducted a field experiment at a reward-based crowdfunding platform by randomly contributing small funding amounts to some campaigns while keeping track of a non-manipulated control group. Our findings support the notion of reverse herding. The number and amount of contributions by the crowd following our small funding amounts were fewer and smaller than in the control group. We discuss reverse herding in relation to established crowdfunding concepts and formulate a dilemma of small contributions: Although small contributions are a fundamental part of crowdfunding, they can also cause the detrimental effect of reverse herding. Practical and theoretical implications of reverse herding are discussed and several opportunities for future research are outlined.
Autor: Zaggl, Michael A. & Block, Jörn

The choice between uniqueness and conformity in mass customization
Expand Abstract
Extant research emphasizes that consumers use mass customization toolkits to create products they consider to be unique, and that perceived uniqueness is an important part of customer value. This research investigates the conditions of the customer's quest for uniqueness. It is motivated by the observation that decisions are often driven by others’ choices and a desire to fit in, rather than to be distinct. We hypothesize that consumers are more inclined to choose uniqueness for hedonic product attributes but tend toward conformity in utilitarian attributes, and that consumers’ need for uniqueness and product involvement moderate the choice. In a series of experiments, we find support for most hypotheses. We introduce conformity as a driver of choice behavior in mass customization toolkits and suggest that mass customization can best be seen as enabling consumers’ preferred mix of uniqueness and conformity. Our results also inform managerial practice, highlighting that mass customization toolkits should consider customers’ uniqueness and conformity requirements. We suggest reducing the number of utilitarian options while increasing the variety for hedonic attributes.
Autor: Zaggl, Michael A.; Hagenmaier, Markus A.; Raasch, Christina

Facilitators and inhibitors for integrating expertise diversity in innovation teams: The case of plasmid exchange in molecular biology
Expand Abstract
Innovation increasingly relies on collaboration in teams instead of individual efforts. Although the advantages of teams for innovating are virtually undisputed, we have only a very rudimentary understanding of their success drivers. To shed more light on innovation teams, we conceptualize multiplicity in expertise as nonredundant expertise and distinguish it from factors that facilitate or hinder the integration of this expertise. These factors are overlap in expertise, disparity in team members’ status, and whether or not teams use automation technology. We use the empirical context of molecular biology, especially the part of this field in which teams produce and exchange genetic material in the form of so-called plasmids. Combining data about plasmids from a central plasmid repository (AddGene) with bibliometric data endows us with a rich dataset capturing information about team diversity in addition to two innovation performance measures (the number of plasmid orders and the number of citations attracted by publications). Our analysis shows that multiplicity in expertise increases innovation performance; this relationship is strengthened by the overlap in expertise and weakened by disparity in status and the use of the automation technology. Our paper provides a more detailed theory of expertise diversity and contributes to the diversity literature. Our findings also lead to implications for practitioners.
Autor: Zaggl, Michael A.; Pottbäcker, Judith

The Dynamics of Openness and the Role of User Communities: A Case Study in the Ecosystem of Open Source Gaming Handhelds
Expand Abstract
To remain competitive, it is critical for firms to integrate external sources of knowledge. However, finding the right degree of openness is challenging, especially in complex open innovation ecosystems. The interdependencies and dynamics related to the choice of openness are not well-understood. This paper investigates the role of openness as a competitive mechanism. Specifically, we research how openness affects firms’ interactions with user communities and how it changes the preference structure of customers. We build a longitudinal case study in the open source gaming handheld industry and trace the evolution and the dynamics of firms, user communities, and their interactions. We find that a suboptimal level of openness can pose a threat to a firm's very existence. Further, we identify repeated patterns characterizing the dynamics in the ecosystem. Based on these patterns, we propose a framework of the dynamics of openness. Our paper contributes to the literature on open innovation. We illuminate the relevance and the dynamics of openness as a dimension for competition. This paper also contributes to the literature on user innovation by showing a shift from manufacturer-based to user-based innovation over the course of the product lifecycle.
Autor: Zaggl, Michael A.; Schweisfurth, Tim G.; Herstatt, Cornelius
Konferenzbeiträge

TOWARDS SYSTEMATIC INCONSISTENCY IDENTIFICATION FOR PRODUCT SERVICE SYSTEMS
Expand Abstract
Value shift towards services led to emergence of product-service systems (PSS) as intertwined products and services. PSS development requires collaborating teams with higher domain diversity to tackle service side as well as product side. Since every domain employs a particular set of tools and models, it is challenging to manage consistency among them. However, the PSS literature lacks approaches for managing inconsistency among various type of models. This study proposes a framework that supports establishing a systematic solution for inconsistency identification during PSS development.
Autor: Basirati, Mohammad R.; Zou, Minjie; Bauer, Harald; Kattner, Niklas; Reinhart, Gunther; Lindemann, Udo; Böhm, Markus; Krcmar, Helmut; Vogel-Heuser, Birgit

Can we Adopt the Toyota Kata for the (Re-) Design of Business Processes in the Complex Environment of a Manufacturing Company?
Autor: Brandl, F. J., Ridolfi, K. S., & Reinhart, G.

Cycle-oriented Evaluation of Production Technologies: Extending the Model of the Production Cycle
Expand Abstract
Permanently evaluating and adopting suitable production technologies due to the dynamic environment is a major challenge for producing companies. However, influencing factors that show cyclic behavior can be anticipated and are predictable to a certain extent. Thus, lifecycle models facilitate the forecast of predictable factors and assist in deriving recommendations for action timely. The developed cycle-oriented planning and evaluation approach provides a cycle stage specific technology requirements profile. The conceptual framework ascertains the suitability of established production technologies using fuzzy sets to meet the vagueness inherent in soft requirements. The presented extension of the production cycle model provides a holistic framework to identify deficits concerning properties of established production technologies proactively. This enables a continuous technology evaluation approach resulting in the timely identification of technological need for action.
Autor: Dengler, C.; Schönmann A.; Lohmann, B.; Reinhart G.

Recurrent Takagi-Sugeno Fuzzy Interpolation for Switched Linear Systems and Hybrid Automata
Autor: Diepold, K. J.; Pieczona, S. J.

Business Model Innovation and Stakeholder Exploring Mechanisms and Outcomes of Value Creation and Destruction
Expand Abstract
Determining the influencing factors of business performance is an
important topic in theory and practice. This applies especially to the
entrepreneurship context, characterized by extreme uncertainty and high failure
rates. Existing research, which is mainly qualitative, has identified business
models (BM) as a performance determinant. This paper empirically examines the
relationship between BMs and startup performance. The analysis follows an
industry- and region-independent approach and is based on a dataset of 121
startups. The findings reveal that some BM patterns outperform others, but on
different performance measures. More specifically, the contractor pattern
enhances revenue, add-on highly influences growth, customer lock-in boosts
valuation, and advertising enhances funding. On the theoretical level, this paper
enriches the qualitative research with statistical evidence. On the practical level,
it adds value to both entrepreneurs and investors by identifying successful
patterns. The findings guide entrepreneurs in BM design and support investors
when considering potential investment opportunities.
Autor: Haddad, H., Weking, J., Hermes, S., Böhm, M., & Krcmar, H.

Business Model Innovation and Stakeholder Exploring Mechanisms and Outcomes of Value Creation and Destruction
Expand Abstract
Given the objective of the focal firm to generate value for stakeholders, this research aims at assessing mechanisms and outcomes for value creation and destruction between business model innovation (BMI) and stakeholders. To achieve this goal, we conduct a systematic literature review and apply grounded theory as coding scheme. Taking frequent mechanisms and outcomes into account, we construct a conceptual framework and pioneer theory building. As main result, we identify BMI creating economic return for third parties and product/service access for customers. Both outcomes are based on the mechanism of altering resources and processes. In contrast, analyzing stakeholder’s main influence, we find management creating strategic orientation by providing know-how. Our research agenda emphasizes the design of BMI from an ecosystem perspective and the destructive consequences of BMI. While the ecosystem level of analysis provides new insights into the concept, investigating negative impacts contributes to a more holistic understanding of BMI.
Autor: Hermes, Sebastian; Böhm, Markus; Krcmar, Helmut

Archetypes for Industry 4.0 Business Model Innovations
Expand Abstract
Industry 4.0 (I4.0) also known as the fourth industrial revolution has emerged for describing the digitalization of manufacturing industries. In practice, the transition to I4.0 is crucial for manufacturing firms to sustain competitive advantage and seize new opportunities. Most research focuses on the technological aspects of I4.0 in form of product and process innovations. Despite I4.0’s rising attention among both researchers and practitioners, there exists only little research about I4.0 business model innovation (BMI), even though business model (BM) innovators can be more successful than product or process innovators. To address this research gap, we analyze 15 case studies of I4.0 BM innovators. We develop a taxonomy to characterize I4.0 BMs and derive 13 archetypes of I4.0 BMIs that describe transitions towards I4.0 BMs. The three identified super-archetypes are integration, servitization and expertise as a service. Our study deepens the understanding and structure of I4.0 BMs and I4.0 BMIs.
Autor: Hermes, Weking, Jörg; Stöcker, Maria; Kowalkiewicz, Marek; Böhm, Markus; Krcmar, Helmut

A Framework for Managing Innovation Cycles in Manufacturing Systems
Expand Abstract
Managing innovation cycles in manufacturing is a key challenge within a volatile business environment characterized by product diversity, individualization, digitalization, interdisciplinary teams and emerging technologies. Shorter product and technology life cycles demand proactive innovation and high efficiency of existing manufacturing technologies at once. A great range of approaches, models, and tools is available in scientific literature, yet managing innovation cycles in manufacturing is associated with great effort, willingness to take risks, strategic vision, and operational capabilities. This paper defines a framework for cyclic innovation management in manufacturing systems in order to enable manufacturing companies to manage technological innovation with ambidexterity.
Autor: Hofer, A., Brandl, F., Bauer, H., Haghi, S., & Reinhart, G.

When to Signal? The Contextual Conditions for Career-Motivated User Contributions in Online Collaboration Communities
Expand Abstract
This paper examines the contextual conditions for users’ career concern as a motivational driver of contributions in online collaboration communities. On the data of user-level activities from a computer programming-related online Q&A community (Stack Overflow), merged with job-market data for software-developer, we find robust evidence of a positive association between individual users’ career concern and their contributions. More important, we find that this positive relationship is further strengthened through the contextual conditions: the number of vacancies in the job market, the expected salaries from these jobs, and the transparency in the flow of career-related information within the community. We contribute to the literature on motivation in online collaboration communities. Our study thus offers insight into how career concern can be effectively utilized to motivate contributors in these communities. Our findings also foreshadow a possible paradigm change by characterizing online collaboration communities as institutions of career concern and skill signaling.
Autor: Lee, J. J., Park, H. & Zaggl, M.

A Knowledge Based System for Managing Heterogeneous Sources of Engineering Information
Expand Abstract
As ever increasing amounts of engineering information become available, engineers require novel ways to manage this information. Especially in mechatronic engineering, e.g., the engineering of Cyber-Physical Production Systems, engineers from various disciplines are involved, and they represent their knowledge in heterogeneous ways. To be able to efficiently gain an overview of the available information and find the information required, engineers need support. Additionally, awareness regarding interdisciplinary dependencies should be increased to reduce late changes. Such dependency analyses allow engineers to better identify and thus manage potential inconsistencies, which can be expected to reduce development time. The Knowledge Based System presented supports engineers during the design process of production systems by providing an overview of available engineering knowledge, its representation, and associated stakeholders. Additionally, engineers can leverage the underlying holistic information model to create and manage digital twins.
Autor: Ocker, F., Vogel-Heuser, B., Seitz, M., & Paredis, C. J.

Managing Cycles of Innovation Processes of Product-Service Systems
Expand Abstract
Innovation processes are subject to external and internal cycles. Changes in the business environment such as shifting market requirements, technological advances and macroeconomic cycles represent interdependent factors which have a significant influence on the innovation process. Furthermore there is a trend towards offering integrated products and services, so-called product-service systems (PSS). Due to more complex market offerings as well as a higher number of stakeholders involved in the innovation process, these cycles challenge especially companies providing PSS. A lack of knowledge and handling of these cycles and their dependencies and effects leads to problems. Analysing cycles integrates discipline-specific perspectives in innovation processes and takes changes inside and outside companies into account. The focus of this paper is on reoccurring patterns and their content-related and temporal dependencies for different disciplines in companies providing PSS.
Autor: Schenkl, S. A., Behncke, F. G. H., Hepperle, C., Langer, S., Lindemann, U.

Decision Methodology for Planning Product-Service Systems
Expand Abstract
One challenge for product development is the change from solely tangible products to more immaterial goods, such as services. This requires offering more than just a product, but opens new business models on the other side. This deferral is called the product-to-service-shift. Combining products and services to a product-service system (PSS) enable companies to better meet customers’ requirements or to increase customer connectivity and to focus on own core competencies. Since PSS are more complex and more interrelated than stand-alone products, developing PSS requires different methods and frameworks. The planning phase for PSS is relevant for the market success, as most important decisions are made in early stages of product development. For this reason, planning PSS requires special methodical support to enable reliable decisions. In this paper, we built a decision methodology for PSS-planning by combining a process model with several methods from previous works. To evaluate its applicability, we conducted a case study from industrial practice and used the methodology for the planning phase of vehicles. The product’s complexity and organizational requirements were high enough for needing methodological support. The case study reveals the need for the methodology and its benefits in a real application.
Autor: Schmidt, Danilo Marcello; Kammerl, Daniel; Preuß, Alexander; Mörtl, Markus

When Algorithms Go Shopping: Analyzing Business Models for Highly Autonomous Consumer Buying Agents
Expand Abstract
Consumer buying agents (CBAs) are software programs that automate tasks in the consumer buying process (e.g., product search and evaluation). Recently, CBAs have the ability to nearly automate the whole buying process, executing transactions with only minimal human involvement. With the rise of such highly autonomous CBAs, updates to business models (BM) of involved parties are expected (e.g., adding a sales channel and increasing customer value). However, our understanding of BMs for highly autonomous CBAs remains limited. In this work we aim to close this gap. We investigate 23 cases and develop a BM taxonomy for highly autonomous CBAs. We further encode these cases into the taxonomy and derive BM patterns. Our work contributes to research by setting a foundation for the conceptual understanding of BMs for highly autonomous CBAs. Practitioners can use our taxonomy and patterns for strategic guidance and to support BM innovation.
Autor: Weber, M., Kowalkiewicz, M., Weking, J., Bohm, M., & Krcmar, H.

Integration of Scenarios in Product-Service System development - Combining Scenarios, Use Cases and Requirements Traceability
Expand Abstract
In product development, a current innovation driver is the integration of services through a shift towards product-service systems (PSS). Therefore, products are extended by additional services, whereas this discipline integration, combined with a necessary future oriented perspective, requires a systematic support for planning and handling complexity. In this context, increasing transparency as well as a better preparation for future evolvements are key aspects. This contribution supports with a procedure that connects the systematic analysis of the future environment with the product-service system and a corresponding case study. Requirements traceability based on a PSS-model is applied to support the impact assessment of future contextual influences on the PSS. Thereby, planning information is transferred into an engineering perspective.
Autor: Weidmann, D.; Seibel, F.; Becerril, L.; Kattner, N.; Lehr, J.; Mörtl, M.; Lindemann, U.

Practices for Open Business Model Innovation–An Innomediaries Perspective
Expand Abstract
Innovative business models generate competitive advantage and are becoming more important than innovative products or processes. Despite its importance, firms continuously fail to innovate business models. Reasons are inhibiting structures, cultures and missing resources or capabilities. Integrating external stakeholders can help to overcome these barriers. Turning to innovation intermediaries, so-called “Innomediaries” support firms. Innomediaries specialize on the integration of suppliers, customers, or inventive partners (startups or universities) into innovation projects. With three in-depth case studies, we provide an actionable framework for integrating external stakeholders into business model innovation. It guides firms when, with whom, and how they can integrate external stakeholders to reduce risks and accelerate the creation of innovations. We shed light on the understudied intersection of open innovation and business model innovations and the linking role of innomediaries. Future research can extend the role of IT, protection against opportunistic behavior, and innomediaries as service platforms in innovation ecosystems.
Autor: Weking, J., Lupberger, J., Hermes, S., Hein, A., Böhm, M., & Krcmar, H.

Why Can’t You See What I Can? Reputation Allocation for Solitary Innovators and Fluid Teams
Expand Abstract
In many distributed innovation systems, the “true” skills of the actors are hidden and reputation is the only observable proxy. Knowing about the actor skills is essential for evaluators and recruiters to predict actors’ future performance. In this paper, we build a theory on reputation allocation. Using a simple agent-based simulation model, we explore which information should be considered for calculating reputation in order to maximize the alignment between reputation and the underlying skills of actors. We consider several conditions for reputation allocation, most importantly fluid teams, that is when multiple actors produce an aggregated outcome, but reputation needs to be assigned to the individual actors. We relate our model the hiring, specifically hiring in academia. In doing so we challenge current practices of reputation allocation, show their downsides and offer solutions that increase the accuracy of rankings of actors.
Autor: Zaggl, M., & Müller, M.

Integrative Solutions in Online Crowdsourcing Innovation Challenges
Expand Abstract
Online crowdsourcing challenges are widely used for problem-solving and innovation. Existing theory has characterized such challenges as tools for tapping distant knowledge. By building on information processing theory we move beyond this characterization and present a perspective that describes innovation challenges as virtual places in which ideas are not simply submitted or commented upon but knowledge is integrated. This perspective shifts the role of crowdsourcing challenges from mere tools for gathering ideas to representing the locus of innovation. Our perspective suggests that three types of knowledge affect the quality of integrative solutions: elementary ideas, facts, and analogical examples. Based on a large dataset, we find that elementary ideas and analogical examples are related to increased solution quality, while facts are related to decreased solution quality. We expand the research on online crowdsourcing innovation challenges to include how crowd participants influence the quality of solutions through the content of their postings.
Autor: Zaggl, M., Sun, Y., Majchrzak, A. & Malhotra, A.

Hierarchical Distance and Idea Evaluation in Enterprise Crowdfunding
Autor: Zaggl, M. A.; Schweisfurth, T.; Schöttl, C. P.; Raasch, C.

Efficiently Learning a Distributed Control Policy in Cyber-Physical Production Systems Via Simulation Optimization
Expand Abstract
The manufacturing industry is becoming more dynamic than ever. The limitations of non-deterministic network delays and real-time requirements call for decentralized control. For such dynamic and complex systems, learning methods stand out as a transformational technology to have a more flexible control solution. Using simulation for learning enables the description of highly dynamic systems and provides samples without occupying a real facility. However, it requires prohibitively expensive computation. In this letter, we argue that simulation optimization is a powerful tool that can be applied to various simulation-based learning processes for tremendous effects. We proposed an efficient policy learning framework, ROSA (Reinforcement-learning enhanced by Optimal Simulation Allocation), with unprecedented integration of learning, control, and simulation optimization techniques, which can drastically improve the efficiency of policy learning in a cyber-physical system. A proof-of-concept is implemented on a conveyer-switch network, demonstrating how ROSA can be applied for efficient policy learning, with an emphasis on the industrial distributed control system.
Autor: Zou, M., Huang, E., Vogel-Heuser, B., & Chen, C. H.

Efficiently Learning a Distributed Control Policy in Cyber-Physical Production Systems Via Simulation Optimization
Expand Abstract
With the increasing integration of multiple disciplines, Model-Based Systems Engineering (MBSE) has become more beneficial for the development of automated production systems. However, even though discipline-specific models can be connected via a system model, how to apply MBSE in a cross-disciplinary context in the industry remains challenging due to complex organization, inefficient communication and limited knowledge of the staff. In this paper, a workflow of automated production system development combining MBSE, sociology and team collaboration is proposed and leveraged against the traditional workflow. BPMN+I is applied for modeling cross-disciplinary collaborations and assessing team and organizational factors.
Autor: Zou, M., Vogel-Heuser, B., Sollfrank, M., & Fischer, J.

Requirements Engineering for IT-enabled Product Service Systems
Companies face the challenge of increased competitive pressure. The differentiation by physical products or services alone is no longer sufficient for coping with this challenge. For this reason, companies offer integrated bundles of physical products and services known as Product Service System (PSS). Requirements engineering has the task of eliciting and managing the requirements. It plays an essential role in the development of PSS. In this thesis an integrated approach for requirements engineering for PSS was developed. The approach describes the content of a specification and defines structuring principles for requirements. Thereby, it supports the interdisciplinary elicitation and concretization of requirements to PSS in accordance with the development process. A comprehensive evaluation of the approach shows its applicability and advantageousness.
Autor: Berkovich, Marina Document type: Dissertation

PS³ - Development and evaluation of a method for scenario-planning of product-service systems based on a creative problem-solving process using analogies
PS³ enables scenario-planning of product-service systems based on a creative problem-solving process using analogies. Starting point for developing PSS scenarios are problems of customers along the customer activity cycle. A PSS scenario combines existing solution components from comparable problems and describes a reasonable flow of events to solve the problem from a customer-centric perspective. The method was evaluated with experiments by applying it to a problem from the area of mobility.
Autor: Fähling, Jens Document type: Dissertation

Customer Integration 4.0: Leveraging Customer Knowledge in Innovation Processes by Using Digital Technologies
Companies increasingly open their innovation processes to integrate external stakeholders such as customers. This thesis provides a decision support system, an ontology, and a software platform for knowledge management in customer integration as well as guidelines for the design of IT-based customer integration methods with regards to usability and user experience. The thesis takes a mixed-methods research approach by combining qualitative and quantitative research methods.
Autor: Füller, Kathrin Document type: Dissertation

Interdisciplinary structural modeling of mechatronic production systems using SysML4Mechatronics
This thesis presents a modeling approach for the development of the interdisciplinary system structure of mechatronic production systems, which is based on SysML, a well-established language in systems engineering. Thus, a consistent, cross-disciplinary comprehension of the overall system in the development and a basis for a model-based analysis of change impacts are achieved. The approach was verified and evaluated with a prototypical implemented modeling editor through use-cases and experimental groups.
Autor: Kernschmidt, Konstantin Emanuel Thassilo Document type: Dissertation
Books

Innovationsprozesse zyklenorientiert managen
Moderne Unternehmen müssen komplexe Innovationsprozesse beherrschen können. Die, für Probleme ursächlichen, wechselseitigen Abhängigkeiten werden von den Autoren analysiert, modelliert und Lösungsvorschläge dargestellt. Hierbei werden Möglichkeiten zur Verbesserung der Innovationsprozesse integrierter Sach- und Dienstleistungen (Produkt-Service Systeme (PSS)) aufgezeigt. Effektivität und Effizienz der Innovationsprozesse, die aus unterschiedlichen Perspektiven betrachtet werden, sind dabei zentrale Schwerpunkte, denn darin liegen die wesentlichen Herausforderungen innovativ wirkender Unternehmen in der Industrie.

Handbuch Industrie 4.0 Bd.2
Experten aus Wissenschaft und Technik beleuchten verschiedene Facetten der Industrie 4.0 sowohl aus akademischer als auch aus praktischer Sicht und schaffen gleichermaßen einen Überblick über den Stand der Technik und die Vision selbst. Dies gelingt nicht zuletzt mit einer guten Mischung aus wissenschaftlichen Erkenntnissen, Praxisbeispielen und Übersichtsbeiträgen. Thematisch reicht das Spektrum von Basistechnologien (z. B. cyber-physische Systeme) über Integrations- und Migrationsansätze bis hin zu Geschäftsmodellen und Dienstleistungen. Zudem werden neben der Datensicherheit auch rechtliche Aspekte thematisiert.
Articles

Diagnose von Inkonsistenzen in heterogenen Engineeringdaten
S. Feldmann & B. Vogel-Heuser Handbuch Industrie 4.0 Produktion - Automatisierung und Logistik

Konzept eines wissensbasierten Frameworks zur Spezifikation und Diagnose von Inkonsistenzen in mechatronischen Modellen
S. Feldmann & B. Vogel-Heuser Handbuch Industrie 4.0 Produktion - Automatisierung und Logistik

Innovationen managen in disruptiven Umgebungen
- Zyklische Einflussfaktoren prägen Nutzungsverhalten von PSS - Anforderungen der Nutzer an PSS verändern sich

Impulsvortrag: Nocole Wagner und Bernhard Artmüller (ZWK-Group)
Referent: Nicole Wagner Ing. Bernhard Artmüller

Technisches Änderungsmanagement (PE)
TP-Leiter: Prof. Udo Lindemann Bearbeiter: Nepomok Chucholowski, Martina Wickel

Management von dynamischen Anforderungen und Zielen (Winfo)
Referent: Thomas Wolfenstetter

Management von Produktionsänderungen (iwb)
Referent: Jonas Koch
Talks

Management von Innovationszyklen im Spannungsfeld zwischen kurzlebiger Software und langlebigen Investionsgütern
Autor: Prof. Dr.-Ing. Birgit Vogel-Heuser