Yiran Zhang

Sy-Thanh Ho

Nicolas Lad

Huyen Nguyen

C Édric Fleury

Patrick Bourdot

In Touch with Everyday Objects: Teleportation Techniques in Virtual Environments Supporting Tangibility

Keywords:

The application of virtual reality (VR) for everyday use is often limited due to the lack of tactile and kinesthetic feedback. To facilitate and expand the use of VR in daily life, it is possible to employ physical objects readily available at home as tangible objects to provide this missing feedback. For instance, a real chair can allow a user to sit within the virtual environment, even if the sitting place in the virtual world is not a chair. In home-based games, a real but not dangerous stick can provide the holding sensation of a virtual sword. These tracked objects in the real world can serve as a tangibility medium to their virtual counterparts, contributing to a higher sense of presence and immersion. However, such a solution relies on a consistent spatial relationship between the real and virtual space surrounding the user, which makes the basic use of virtual navigation techniques such as teleportation difficult. To allow the navigation on a large virtual environment while supporting a tangible interaction with real objects in a limited physical space at home, this paper explores three different teleportation techniques: to teleport the user, the object, or both of them to a new position accordingly while preserving the user and object's spatial relationship. All of these approaches enable tangible interaction when using a teleportation technique for navigation, but each one is more or less suitable in different situations of real/virtual spatial consistency.

INTRODUCTION

The use of virtual reality (VR) has been steadily grown in our daily life, such as at homes and offices, thanks to the affordability of off-the-shelf display headsets and the exponential development in applications and games. This growth, therefore, emphasizes the urgency to consider and study user experience for their adoption of VR applications in everyday life. Haptic technology is one of the VR technologies whose objective is to enhance the realism and immersion of user experience with a sense of touch [START_REF] Hoffman | Physically touching virtual objects using tactile augmentation enhances the realism of virtual environments[END_REF].

Indeed, many haptic devices on the market use different modalities and techniques to provide a user with tactile sensation, including pressure, skin stretch, vibration, and temperature. As opposed to dedicated VR setups found in academic labs or big companies, these devices are not always available at home or in SME offices, and they are quite expensive for the general public. Therefore, tactile and kinesthetic feedback is usually absent in home-based VR applications.

To address this limitation, some previous works propose to integrate everyday objects into a virtual environment by pairing them with their virtual counterparts. For example, an umbrella can represent Darth Vader's lightsaber [START_REF] Simeone | Substitutional reality: Using the physical environment to design virtual reality experiences[END_REF], or a suspended ball can be deployed as a flying droid that physically attacks the user [START_REF] Cheng | iturk: Turning passive haptics into active haptics by making users reconfigure props in virtual reality[END_REF]. The main idea is to employ some tangible objects in the real working space, which provide passive haptic feedback [START_REF] Hoffman | Physically touching virtual objects using tactile augmentation enhances the realism of virtual environments[END_REF] realistic enough in terms of tactile-kinesthetic sensation. Therefore, the user can perceive a haptic feeling when touching the virtual objects. This simple and cost-effective approach enhances the perception of virtual object affordances [START_REF] Gibson | The theory of affordances[END_REF], improves the user's sense of presence, and contributes to a more compelling VR experience. However, this approach is also subjected to its limitations when applied in some scenarios, particularly accompanied by virtual-navigation techniques [START_REF] Bowman | Travel in immersive virtual environments: An evaluation of viewpoint motion control techniques[END_REF][START_REF] Chen | 6DoF navigation in virtual worlds: comparison of joystickbased and head-controlled paradigms[END_REF][START_REF] Habgood | Rapid, continuous movement between nodes as an accessible virtual reality locomotion technique[END_REF][START_REF] Weiβ Ker | Spatial updating and simulator sickness during steering and jumping in immersive virtual environments[END_REF].

In our context, enabling the user to touch a virtual object via a tangible prop highly relies on the consistent spatial relationship between the user, the tangible object, and its virtual counterpart. Although allowing the user to carry out virtual navigation is mandatory in many large-scale virtual environments, a major issue is that such techniques easily break the one-to-one mapping between the virtual and real space surrounding the user. Consequently, after the virtual navigation, the tangible objects will no longer be located at their counterpart position in the virtual world. Once the user releases a tangible object before the virtual navigation, it becomes impossible for them to find and touch it again afterwards while still wearing the VR headset. Therefore, virtual navigation techniques are usually excluded when there are tangible objects involved, limiting the user's available interaction space in the virtual environment to their real space.

In this paper we propose three interactive techniques to allow the user to navigate in a large-scale virtual environment while preserving the possibility to interact with virtual objects and their real/tangible counterparts. These techniques are to some extent based on the basic teleportation navigation technique [START_REF] Bowman | Travel in immersive virtual environments: An evaluation of viewpoint motion control techniques[END_REF], this latter being widely used in many VR applications and known as limiting simulator sickness compared to other virtual navigation techniques [START_REF] Habgood | Rapid, continuous movement between nodes as an accessible virtual reality locomotion technique[END_REF][START_REF] Weiβ Ker | Spatial updating and simulator sickness during steering and jumping in immersive virtual environments[END_REF]. Our techniques aim to teleport either the user, the virtual object, or both of them to a new position, to recover the spatial relationship which makes a consistent mapping between the user, the virtual object, and its tangible counterpart possible after teleportation.

Passive haptics [START_REF] Hoffman | Physically touching virtual objects using tactile augmentation enhances the realism of virtual environments[END_REF] allows the user to have tactile and kinesthetic feedback in the virtual world by physically touching a tangible object in the real world. This concept has been widely used in many VR applications. For example, the iTurk system [START_REF] Cheng | iturk: Turning passive haptics into active haptics by making users reconfigure props in virtual reality[END_REF] complements the VR experience with a foldable object as a physical prop that can be reconfigured as a suitcase or a fuse box in the virtual world. This iTurk system focuses on the mapping of only one physical object to several virtual objects of the similar form and shape. Meanwhile, the Substitutional reality system [START_REF] Simeone | Substitutional reality: Using the physical environment to design virtual reality experiences[END_REF] pairs every physical object and architectural feature surrounding the user to its virtual counterpart, but still allows some degree of discrepancy between them.

Adding physical qualities to virtual objects can enhance the sense of presence of the user. Indeed, in the study of Hoffman et al. [START_REF] Hoffman | Physically touching virtual objects using tactile augmentation enhances the realism of virtual environments[END_REF], participants who were allowed to "touch and see" the object had more accurate prediction of object properties than those who were only allowed to "see" it. Insko et al. [START_REF] Insko | Passive haptics significantly enhances virtual environments[END_REF] showed that augmenting a visual-cliff environment with a real wooden plank as a ledge significantly impacted participants' behavioral presence, heart rate, and skin conductivity compared to a virtual-ledge-only condition. Moreover, in their experiment, they demonstrated that using passive haptics could lead to significant increase in presence and spatial knowledge training transfer. Besides, passive haptics can also be applied in medical fields. For example, allowing patients to touch a spider replica's furry texture can enhance the treatment of spider phobia [START_REF] Carlin | Virtual reality and tactile augmentation in the treatment of spider phobia: a case report[END_REF]. In the work of Kotranza and Lok [START_REF] Kotranza | Virtual human+ tangible interface= mixed reality human an initial exploration with a virtual breast exam patient[END_REF], augmenting a virtual patient with a tangible interface makes the interaction during a breast exam more similar to human-human interaction.

Passive haptics usually requires a one-to-one mapping between real and virtual object. This mapping limits the use of passive haptics in many VR applications that may introduce spatial discrepancies between the user's real and virtual world, for instance, when using virtual navigation in large-scale virtual environments. Moreover, a physical prop can often match only one specific type of virtual objects, limiting its use in a complex VR experience. These problems can be overcome by reconfiguring the physical prop during its use with the help of robots or human actuators. For example, robotic graphics [START_REF] Mcneely | Robotic graphics: a new approach to force feedback for virtual reality[END_REF] uses a robotic arm to correctly place a real object in front of the user's hand when they try to reach for a virtual object. Snake charmer [START_REF] Araujo | Snake charmer: Physically enabling virtual objects[END_REF] not only aligns a robotic arm with the object's virtual representation but also allows the user to feel one or more of object's shape, texture, and temperature. In addition to using robots, some applications such as TurkDeck [START_REF] Cheng | Turkdeck: Physical virtual reality based on people[END_REF] employ a group of human workers to operate props to create a physical world adapting to the user's activities in the virtual world. However, using robot technologies or employing a team of human actuators are difficult in everyday VR experience.

Some redirected techniques can solve the passive haptic inflexibility. For example, redirected touching [START_REF] Kohli | Redirected touching: The effect of warping space on task performance[END_REF][START_REF] Kohli | Redirected touching: Training and adaptation in warped virtual spaces[END_REF] and haptic retargeting [START_REF] Azmandian | Haptic retargeting: Dynamic repurposing of passive haptics for enhanced virtual reality experiences[END_REF] introduce a discrepancy between the user's real and virtual hand motion. As the user's hand movement in the virtual environment is no longer the same as their real-world motion, the real and virtual hands can reach the real and virtual objects at the same time. By generating different mappings between the real and virtual spaces, a single physical object can provide haptic feedback for various virtual objects with different shapes. However, people also reported strange sensations as the virtual space is warped to map a variety of virtual objects onto a single real object, and a phase of adaption is necessary to achieve the same task performance as in the non-warped condition [START_REF] Kohli | Redirected touching: Training and adaptation in warped virtual spaces[END_REF].

In the context of navigation by real walking, redirected walking [START_REF] Kohli | Combining passive haptics with redirected walking[END_REF] enables a single real prop to provide tangibility to multiple virtual objects by introducing an offset between the user's physical and virtual path. Although the user is usually not aware of the offset, this technique often requires physical spaces larger than 6m × 6m [START_REF] Azmandian | Physical space requirements for redirected walking: How size and shape affect performance[END_REF], and is therefore not suitable for domestic use. For a compact tracking volume, Impossible space [START_REF] Suma | Impossible spaces: Maximizing natural walking in virtual environments with self-overlapping architecture[END_REF] deploys a selfoverlapping architectural layout of the virtual environment to allow the user to walk through multiple rooms via portals. The adjacent virtual room is physically overlapping with the previous one, allowing the user to reuse the same physical props in the new room. However, the specific architectural layout also imposes limitations on the design of the virtual environment.

Based on the limitations observed in these previous research works regarding everyday and/or domestic uses, this paper proposes three interaction techniques and discusses their complementary interests to help the user recover the spatial consistency during teleportation, with the tangible interaction support. Our techniques are suitable for small tracking volumes, such as domestic rooms and offices, and do not depend on a specific virtual environment layout. In addition, a single physical object can be reused to link with multiple similar virtual objects located in different places without introducing an offset.

TANGIBILITY SUPPORTED BY TELEPORTATION

The basic idea of our techniques is to teleport either the user, the virtual object, or both of them at once to a new position calculated based on the spatial relationship between the tangible object and the user. Indeed, the relationship between the user and the virtual object must be aligned with the spatial arrangement between the user and the tangible prop to recover the consistency and coherence of these components after the teleportation. Moreover, when tangible interactions are not required, during basic virtual navigation for example, the surrounding real objects are not aligned with any visual ones. Therefore, by using the spatial consistency recovering technique, the potential collisions between the user and those real-world tracked objects can be avoided using some specific visual feedback [START_REF] Lacoche | Collaborators awareness for user cohabitation in co-located collaborative virtual environments[END_REF].

In the following sub-sections, we will present the design and implementation of three different advanced teleportation techniques to support tangible interaction. As an example of possible applications of these teleportation techniques, we designed a VR environment that incorporates a tracked physical chair in the real world to allow the user to rest on it. This chair also has a virtual counterpart with which the user can interact in the virtual world. However, the use cases associated with each technique can be extended into more general situations in everyday VR applications with different physical objects involved.

The VR setup of our proof-of-concept implementation consisted of an HTC Vive headset and two controllers. The virtual environment was rendered using Unity 2019.4.2f1 with a resolution of 1080 × 1200 pixels per eye at 90 Hz. The room supported a 3m × 5m tracking area, and the real chair was tracked using one Vive Tracker.

Depending on the working context in the virtual environment, the user can select from a virtual menu at runtime the teleportation technique they want to use to connect virtual objects with their tangible counterparts. For instance, to interact with the virtual object and its physical counterpart in its current virtual context, the user can teleport himself close to the targeted object. On the contrary, if the current interaction context is not important to the user and the task at hand, the second technique can be applied to bring the object close to the user. Finally, if the user wants to use a virtual object at another place in the virtual environment, the hybrid technique can be activated.

Teleportation of the User

In this technique, the selected virtual object becomes an anchor of the teleportation. The system will calculate the user's avatar future position to reflect their actual position related to the physical object in the real world (see Fig. 1). After teleportation, the user can reach and interact with the real object using its virtual counterpart thanks to the recovered spatial consistency. To preserve the existing spatial relationship in the real world, the number of the possible future positions for the user's avatar in the virtual environment is decided by the number of the physical props integrated as well as their forms, shapes and potential mobility. For example, if we pair the ball suspended from a long pendulum with a virtual flying droid as in iTurk system [START_REF] Cheng | iturk: Turning passive haptics into active haptics by making users reconfigure props in virtual reality[END_REF], the number of possibilities to position the user near the ball in the virtual environment tends to be infinite. However, in Substitutional reality system [START_REF] Simeone | Substitutional reality: Using the physical environment to design virtual reality experiences[END_REF], the mapping is unique since every architectural feature should pair to its virtual object. Besides, the possible future positions of the user's avatar also depend on the actual context of the virtual scene if the system wants to maintain a semantic coherence. For example, the system can help prevent the user from being positioned behind a virtual obstacle or in the middle of surrounding virtual object after the teleportation.

Although the user has the possibility to select an appropriate position amongst multiple options computed by the system, it is sometimes unavoidable when the user has no choice but to teleport into a virtual object to maintain the spatial relationship. In particular, it often happens when many virtual objects surround the target one. However, teleporting the user inside or in the middle of a virtual object can break the user's immersion and affect the realism of the virtual environment and VR experience. In order to overcome this issue, the system can show the user's future positions while highlighting the objects currently overlapping with them. The system then guides the user to physically move to a more appropriate position in the real world before triggering the teleportation.

In our implementation, the virtual object with potential tangibility (i.e., the chair) will be highlighted with a different color when the user hovers the laser pointer over it (see Fig. 2). The user can select the virtual object with the pointer and soft trigger the teleportation by pressing the "Grab" button on the Vive controller. Due to the shape of the chair (with backrest), the user has only one possible mapping position for the teleportation. If the user's future position of teleportation overlaps with the nearby virtual objects (e.g., the table), the user needs to physically move (i.e., walk) to a more appropriate position in the real world to be able to complete the teleportation. To achieve this, the system will display a clone of the distant context (the chair and the table that currently overlaps with user's future position) around the user's current position to simulate the scene after teleportation. The available area where the user can physically walk turns green, guiding the user to move to a position to avoid any overlapping. Once the user physically reach a position which is free of obstacles, the teleportation can be hard triggered by pressing the "Squeeze" button and the user will be teleported nearby the targeted tangible object while avoiding teleporting into the surrounding obstacles.

Teleportation of the Object

In this technique of teleportation, instead of moving the user towards the virtual object as mentioned in Section 3.1, it is also possible to bring the targeted virtual object to the user to recover the spatial relationship relating to the tangible object. Based on the actual position of the user's avatar in the virtual environment, we can compute the virtual object's future position in relation to its tangible prop (see Fig. 3). Different from the first technique which teleports the user's avatar, the resulted position is unique in this case. However, this position can be probably occupied or blocked by other virtual obstacles (e.g., a virtual wall) surrounding the user. In this case, the system detects post-teleportation interference and computes a new position to which the user has to teleport themself before completing the object-based teleportation operation.

To compute such position, the system first finds a new position for the targeted virtual object outside the obstacle. A basic approach is to use the point on the obstacle's collider that is closest to the virtual object's current teleportation destination. Then, based on this new position of the targeted virtual object, the system computes the new corresponding position for the user's avatar in relation to their physical position in the real world (see Fig. 4). Consequently, the targeted virtual object will no longer overlap or be blocked by other virtual objects after the teleportation. However, in some crowded virtual environments, the resulted user's position computed from this basic approach can also be occupied by other obstacles in the scene (see Fig. 5). In this case, another configuration for the couple of virtual chair and the avatar of the user can be computed using the Probabilistic RoadMap (PRM) sampling approach [START_REF] Kavraki | Probabilistic roadmaps for path planning in high-dimensional configuration spaces[END_REF].

Similar to the first technique, our implementation allows the user to select the targeted virtual object (i.e., the chair) and teleport the object towards the user. By pressing the "Grab" button on the controller, the user can soft trigger the teleportation. The system will show a clone of the targeted object at the computed position to inform the user of its future position (see Fig. 6). If the virtual object destination is occupied or blocked by other virtual objects, those obstacles will be highlighted. In this case, the user is then asked to teleport himself to a new position (presented as a green zone on the ground) in the virtual world before teleporting the object. After reaching such suitable virtual position, the user can hard trigger the teleportation of the object with the "Squeeze" button. The targeted virtual object then will be teleported nearby the user.

Hybrid Teleportation Technique

As the name suggests, the hybrid technique is an ultimate approach to resolve the spatial consistency recovery problem by combining the first two techniques mentioned in Section 3.1 and 3.2. Similar to group teleportation [START_REF] Weissker | Multi-ray jumping: comprehensible group navigation for collocated users in immersive virtual reality[END_REF], this technique allows the user to teleport the targeted virtual object and themself simultaneously to support a tangible interaction at a specific destination in the virtual world. However, their spatial relationship needs to be recomputed with regard to the spatial arrangement between the user and the physical prop (see Fig. 7).

Our hybrid technology deploys a virtual representation that couples the teleportation destinations of the user and the virtual object according to the current relative position between the user and the tangible object. By manipulating such virtual representation's position and rotation, the user can simultaneously define the teleportation destination for the targeted virtual object and themself. Thus, the user can customize the teleportation for different virtual contexts, optimizing the obstacle-related situations (e.g., obstruction, overlapping). At the same time, the teleportation provides tangible interactions for the user.

Unlike the other two implementations, the user soft triggers the teleportation with the "Pinch" button after selecting the targeted virtual object (i.e., the chair). The user can define their future position using the laser pointer. Based on this position, the system will calculate the corresponding position of the virtual object to maintain the spatial relationship between the physical object and the user, and display a clone of the target virtual object at the resulting position (see Fig. 8). By pressing the "Touch left" and "Touch right" buttons of the other controller, the user can rotate the clone object around the their future position to make sure that the user or the object will not teleport into any other obstacles afterwards. Finally, by pressing the "Pinch" button again, the user and the virtual object can be teleported to the predefined position with a recovered spatial relationship.

CONCLUSION

Allowing a user to touch or hold virtual objects can enhance immersion and contributes to a greater sense of presence. Passive haptic is a simple and cost-effective solution to compensate the lack of haptic feedback in domestic use of virtual reality by using everyday objects as tangible props for virtual objects. However, passive haptic requires a one-to-one mapping between tangible props and their virtual counterparts, which usually hinders virtual navigation in large-scale virtual environments.

To overcome this issue, we propose three techniques to help the user to recover the spatial consistency between a targeted virtual object and its physical counterparts after teleportation: teleportation of the user, teleportation of the object and hybrid teleportation. Decided by the targeted virtual object's position, teleportation of the user technique teleports the user to a position near the virtual object to restore the spatial relationship. Different positions can be proposed to the user according to the shape, size and number of integrated tangible props. Based on the user's position in the virtual environment, teleportation of the object technique computes the virtual object's position corresponding to its tangible prop, and teleports the object to this unique position. Finally, hybrid teleportation approach combines these two techniques and allows the user to define a new teleportation destination for both the object and themself while restoring the spatial consistency.

These different techniques can be applied in different scenarios according to the targeted object's features. For example, teleportation of the user can be more appropriate than teleportation of the object or hybrid teleportation to allow the user to touch virtual objects that are considered non movable. On the other hand, teleportation of the object or hybrid teleportation may be more suitable for the user to interact with small objects or tools to perform a task at a specific location in the virtual environment. Each of these techniques also has its advantages and disadvantages. For example, teleportation of the user and teleportation of the object require additional strategies to prevent the user or the object from being teleported inside or behind other virtual objects. Hybrid teleportation solves this problem by enabling the user to manage the teleportation location themself. Nevertheless, this technique might be time-consuming and cognitive-challenging to use.

For future work, we will conduct user studies using virtual objects of different shapes, sizes, and potential mobility in various virtual scenarios to evaluate these techniques. It will also be interesting to see if experiencing tangible interactions affects the user's sense of presence and changes their behavior (e.g., with regard to obstacle avoidance) when interacting with purely virtual objects. Finally, security issues should also be considered in such an application, especially in scenarios where the tangible interaction phase alternates with the free navigation phase without tangibility support. This is because tangible props in the real world can also be considered as obstacles for the user during the free navigation.

Figure 1 :

 1 Figure 1: Teleportation of the user's position in the virtual world towards the targeted virtual object's (brown chair) position illustrated from the bird-eye view. Their new position recovers the spatial relationship between them and the object's physical counterpart (black chair).

Figure 2 :

 2 Figure2: Top: the user selects the targeted object (brown chair) to soft trigger the teleportation. Middle: clones of the targeted chair and the surrounding table are displayed close to the user (purple avatar) to inform them of the situation after teleportation. The available walking area turns green to guide the user to a more suitable position to avoid overlapping. Bottom: after physically positioning themself in an appropriate position, the user hard triggers the teleportation and is teleported to the next position while maintaining a consistent spatial relationship with the tangible object.

Figure 3 :

 3 Figure 3: Teleportation of the targeted virtual object (brown chair) towards to the user's actual position illustrated from the bird-eye view. Its future position recovers the spatial relationship between the user and the object's physical counterpart (black chair).

Figure 4 :

 4 Figure 4: Basic approach to compute a valid teleportation destination for the user in the case of the object appearing in a virtual obstacle using Collider.ClosestPoint function of Unity3D.

Figure 5 :

 5 Figure 5: Computation of possible teleportation destinations (in green) using the PRM-based sampling approach on the couple of the virtual chair and the avatar of the user.

Figure 6 :

 6 Figure6: Top: the user selects the targeted virtual object (brown chair) to soft triggers the teleportation of the object. Bottom: a clone of the virtual object is shown in the surrounding of the user (purple avatar). The targeted virtual object is teleported toward to user after the user hard triggers the teleportation.

Figure 7 :

 7 Figure 7: Hybrid teleportation of both the user and the targeted virtual object (brown chair) to their new positions defined by the user while preserving spatial relationship between them.

Figure 8 :

 8 Figure 8: Top: when the user soft triggers the technique, the system displays a clone object at a location calculated based on the user-defined teleportation position. The user has all the freedom to manipulate the future position and orientation of the user and object as a set. Bottom: when the user hard triggers the technique, both the user and the object arrive at the predefined positions with a recovered spatial relationship.


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Pierre Denormandie

Tabassome Simon

Guillaume Cayla

Philippe Gabriel Steg

Gilles Montalescot

Isabelle Durand-Zaleski

Alicia Le Bras

Hervé Le Breton

Yann Valy

François Schiele

Infarction Patients with Multivessel Disease Treated with Primary Percutaneous Coronary Intervention and Preserved Fractional Flow Reserve of Non-Culprit Lesions Treated Conservatively and of Those with Low Fractional Flow Reserve Managed Invasively: Insights from the FLOWER MI trial

published or not. The documents may come


Milan Zdravković
email: milan.zdravkovic@gmail.com

Hervé Panetto
email: herve.panetto@univ-lorraine.fr

Artificial Intelligence-enabled Enterprise Information Systems

Introduction

The fourth industrial revolution has marked the end of the industrial automation era of simple and repetitive human tasks. Then, it opened a new arena for efforts of mimicking human intelligence with a clear objective. This arena facilitates i) machine-driven decision-making, ii) seamless machine-to-machine communication using the formalisms easily expressed and understood by humans, iii) solving problems driven by uncertain and unknown variables, and iv) other activities that require more complex considerations and actions which humans typically implement in the past. With Artificial Intelligence (AI), Enterprise Information Systems (EIS) are becoming increasingly capable of sensing and perceive (even reach beyond the human cognitive horizon), analyse, or understand and respond, based on the acquired understanding. This combination was made possible using big data, significantly improved algorithms, and sufficient computational power to train and run those algorithms with vast amounts of data.

In this Special Issue, the concept of AI EIS enablement [START_REF] Zdravković | AI-enabled Enterprise Information Systems for Manufacturing[END_REF] is introduced to provide the umbrella for a new way of thinking, architecting, designing, developing and using the EIS. It is put on the top of the widely discussed data-enablement, sometimes in the context of socalled sensing enterprise. This enterprise continuously listens to its internal and external environment using the technologies such as sensors, embedded electronics and multi-agent systems. Although today's hype on AI is driven by the performance of complex deep learning architectures and models, both symbolic and non-symbolic AI applications were considered to reflect the equal importance of challenges and opportunities for logic-based and data-based methods.

The Special Issue was advertised on the website of the publisher and by email. Also, the authors of the selected papers from the special session with the title '(Industrial) Internet-of-Things for Smart & Sensing Systems', organized at the 8 th International Conference for Information Society and Technology (ICIST 2018) were invited to submit the extended versions of those papers to the Special Issue. Twenty submissions have been received, and after several rounds of reviews and revisions, 6 manuscripts were accepted for publication. Those manuscripts are shortly presented in the following section.

Discussion

In some domains, many diverse factors for business decisions cannot be represented by the effective analytical, deterministic models. The complexity of data is one typical reason for that, while in some cases, the strong impact of uncertainties makes it even impossible to build accurate predictive models for the support to decision making. Modern supply chains are one example of such a situation. Their planning is largely based on forecasts, which are often driven by very general assumptions and simplifications and thus, they are inaccurate. Supply chains are extremely complex, and their operations are continuously disturbed by the variability in demand, different incidents, etc. The issues caused by this variability and other uncertainties involved in supply chain planning has not been successfully addressed in the past, either with symbolic or non-symbolic AI methods. [START_REF] Oger | A Decision Support System for Strategic Supply Chain Capacity Planning under Uncertainty: Conceptual Framework and Experiment[END_REF]) have worked on the comprehensive model for understanding uncertainties and opportunities in supply chain capacity planning. They proposed a new conceptual framework for decision making for supply chain capacity planning that is developed around the concepts of purpose, people, decision-making process, and information system. The framework has been designed, implemented, and validated in two industrial experiments with success.

A lot of productivity promises of the modern enterprise information systems today are wasted in bottlenecks caused by the lack of interoperability of different modules. Finding the delicate balance of benefits and drawbacks in the spectrum from tight integration to losing interoperability within one EIS is an extremely difficult challenge for the enterprise to excel in both productivity and flexibility. Symbolic AI methods that facilitate the so-called semantic interoperability of systems are today the most promising way to address the above challenge in the long-term sustainably. An interesting case study to support this statement was provided by [START_REF] Marković | A Knowledge-Based Document Assembly Method to Support Semantic Interoperability of Enterprise Information Systems[END_REF]. They proposed the machine-readable documents as messages with which semantic interoperation between systems (for example, those of buyer and seller) would be seamless. The documents are automatically assembled (even inferred) using the knowledge base, consisting of rules from the legislation and document templates. The proposition was successfully validated in the case of service contracts.

Big data availability enabled the breakthrough also in how the product development processes are perceived and implemented today. The industries now use vast data and models collected and developed for product conception, design, development, testing, exploitation, maintenance, and even scrapping to meet the continuously changing and evolving user requirements. [START_REF] Li | Data and Model-Based Triple V Product Development Framework and Methodology[END_REF] proposed the improved V framework for product development by adding advanced data analysis and AI methods in the pipeline. Thus, the model-driven aspect of the product design process introduced by the V framework is not complemented with data-driven functional development.

The methodology and framework were tested in the case of the development of a damage control system-based mission system. While many of the AI applications aim at significantly improving the existing functions, the advance in the specific AI areas has opened the avenues of opportunities for new functions that have not been considered before. Such new functions are very often found in the marketing domain, in specific, in market research. The power of vast social media data about the existing and prospective customers can today be unleashed for uses in market segmentation and targeting by using modern Natural Language Processing methods driven by AI. Sentiment analysis and opinion mining are the tools for the above. However, those techniques rely on so-called language models, which are not yet developed for many local languages. [START_REF] Grljević | Opinion Mining in Higher Education: A Corpus-Based Approach[END_REF] have provided methodology and a case study for creating a corpus for sentiment analysis on the Serbian language. Their case study was related to opinion mining in the higher education domain.

Another breakthrough, jointly achieved by the advances in computational power availability, reliable sensing technologies and algorithms, can produce very complex real-time analysis of different phenomena. Real-time analysis facilitates near real-time response and, consequently, the huge benefits of flexible behaviour of different systems and the prevention of different risks. This is especially important for the health-related risks from environmental phenomena. [START_REF] Tešendić | RealForAll: Real-Time System for Automatic Detection of Airborne Pollen[END_REF] have presented a clear case on how the mix of the advances mentioned above can prevent health risks by proposing the system for airborne pollen detection. The proposed system is built around the airborne particle monitor sensors and CNN (Convolutional Neural Networks)-based algorithms to classify full spectra of allergy relevant airborne pollen types.

The massive rate of digitalization of society, driven by data, algorithms and computational devices, comes with the cost. Security and privacy challenges are significantly increasing. Fast developing legal frameworks put those challenges at the top of the list. The most effective security risk prevention measure is dealing with software vulnerabilities. [START_REF] Siavvas | Technical Debt as an Indicator of Software Security Risk: A Machine Learning Approach for Software Development Enterprises[END_REF] have presented an effective approach in using Technical Debt indicators to indicate software security risk by using Machine Learning algorithms.