CLC number: TP311
On-line Access: 2024-08-27
Received: 2023-10-17
Revision Accepted: 2024-05-08
Crosschecked: 2017-10-12
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Yuan Sun, Gang Yang, Xing-she Zhou. A survey on run-time supporting platforms for cyber physical systems[J]. Frontiers of Information Technology & Electronic Engineering, 2017, 18(10): 1458-1478.
@article{title="A survey on run-time supporting platforms for cyber physical systems",
author="Yuan Sun, Gang Yang, Xing-she Zhou",
journal="Frontiers of Information Technology & Electronic Engineering",
volume="18",
number="10",
pages="1458-1478",
year="2017",
publisher="Zhejiang University Press & Springer",
doi="10.1631/FITEE.1601579"
}
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%A Yuan Sun
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%I Zhejiang University Press & Springer
%DOI 10.1631/FITEE.1601579
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T1 - A survey on run-time supporting platforms for cyber physical systems
A1 - Yuan Sun
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PB - Zhejiang University Press & Springer
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DOI - 10.1631/FITEE.1601579
Abstract: Cyber physical systems (CPSs) incorporate computation, communication, and physical processes. The deep coupling and continuous interaction between such processes lead to a significant increase in complexity in the design and implementation of CPSs. Consequently, whereas developing CPSs from scratch is inefficient, developing them with the aid of CPS run-time supporting platforms can be efficient. In recent years, much research has been actively conducted on CPS run-time supporting platforms. However, few surveys have been conducted on these platforms. In this paper, we analyze and evaluate existing CPS run-time supporting platforms by first classifying them into three categories from the viewpoint of software architecture: component-based platforms, service-based platforms, and agent-based platforms. Then, for each type, we detail its design philosophy, key technical problems, and corresponding solutions with specific use cases. Subsequently, we compare existing platforms from two aspects: construction approaches for CPS tasks and support for non-functional properties. Finally, we outline several important future research issues.
[1]Acosta, F.J., Weis, F., Bourcier, J., 2014. Towards a Model@Runtime middleware for cyber physical systems. Proc. 9th Workshop on Middleware for Next Generation Internet Computing, Article 6.
[2]Afanasov, M., Mottola, L., Ghezzi, C., 2014. Towards context-oriented self-adaptation in resource-constrained cyberphysical systems. Proc. IEEE 38th Annual Int. Computers, Software and Applications Conf. Workshops, p.372-377.
[3]Ahmadi, H., Abdelzaher, T.F., Gupta, I., 2010. Congestion control for spatio-temporal data in cyber-physical systems. Proc. 1st ACM/IEEE Int. Conf. on Cyber-Physical Systems, p.89-98.
[4]Aiello, M., Frankova, G., Malfatti, D., 2005. What’s in an agreement An analysis and an extension of WS-agreement. In: Benatallah, B., Casati, F., Traverso, P. (Eds.), Service-Oriented Computing-ICSOC 2005. Springer-Verlag Berlin Heidelberg, p.424-436.
[5]Al-Safi, Y., Vyatkin, V., 2007. An ontology-based reconfiguration agent for intelligent mechatronic systems. In: Mařík, V., Vyatkin, V., Colombo, A.W. (Eds.), Holonic and Multi-agent Systems for Manufacturing. Springer-Verlag Berlin Heidelberg, p.114-126.
[6]Andersson, B., Pereira, N., Tovar, E., 2008. How a cyber-physical system can efficiently obtain a snapshot of physical information even in the presence of sensor faults. Proc. Int. Workshop on Intelligent Solutions in Embedded Systems, p.1-10.
[7]Asadollah, S.A., Inam, R., Hansson, H., 2015. A survey on testing for cyber physical system. In: El-Fakih, K., Barlas, G., Yevtushenko, N. (Eds.), Testing Software and Systems. Springer International Publishing, Cham, Switzerland, p.194-207.
[8]AUTOSAR, 2014. AUTomotive Open System ARchitecture (AUTOSAR). http://www.autosar.org/about/technical-overview/ [Accessed on Nov. 20, 2016].
[9]Axelsson, J., Kobetski, A., 2014. Architectural concepts for federated embedded systems. Proc. European Conf. on Software Architecture Workshops, p.25:1-25:8.
[10]Barbosa, J., Leitão, P., Adam, E., et al., 2015. Dynamic self-organization in holonic multi-agent manufacturing systems: the ADACOR evolution. Comput. Ind., 66:99-111.
[11]Bellifemine, F., Caire, G., Poggi, A., et al., 2008. JADE: a software framework for developing multi-agent applications: lessons learned. Inform. Softw. Technol., 50(1): 10-21.
[12]Broy, M., 2013. Cyber-physical systems: concepts, challenges and foundations. https://artemis-ia.eu/publication/down load/877-magazine-14.pdf [Accessed on Nov. 20, 2016].
[13]Bruneton, E., Coupaye, T., Leclercq, M., et al., 2006. The FRACTAL component model and its support in Java. Softw. Pract. Exp., 36(11-12):1257-1284.
[14]Bures, T., Gerostathopoulos, I., Hnetynka, P., et al., 2013. DEECO: an ensemble-based component system. Proc. 16th ACM Sigsoft Symp. on Component-Based Software Engineering, p.81-90.
[15]Bures, T., Gerostathopoulos, I., Hnetynka, P., et al., 2014. Gossiping components for cyber-physical systems. In: Avgeriou, P., Zdun, U. (Eds.), Software Architecture. Springer International Publishing, Cham, Switzerland, p.250-266.
[16]Buttazzo, G., 2011. Hard Real-Time Computing Systems: Predictable Scheduling Algorithms and Applications. Springer US, New York, USA, p.1-22.
[17]Chen, B., Cheng, H.H., 2010. A review of the applications of agent technology in traffic and transportation systems. IEEE Trans. Intell. Transp., 11(2):485-497.
[18]Chen, B., Cheng, H.H., Palen, J., 2009. Integrating mobile agent technology with multi-agent systems for distributed traffic detection and management systems. Transp. Res. C-Emerg., 17(1):1-10.
[19]Cucinotta, T., Mancina, A., Anastasi, G.F., et al., 2009. A real-time service-oriented architecture for industrial automation. IEEE Trans. Ind. Inform., 5(3):267-277.
[20]Curbera, F., Duftler, M., Khalaf, R., et al., 2002. Unraveling the web services web: an introduction to SOAP, WSDL, and UDDI. IEEE Internet Comput., 6(2):86-93.
[21]Dillon, T.S., Zhuge, H., Wu, C., et al., 2011. Web-of-things framework for cyber-physical systems. Concurr. Comp.-Pract. E., 23(9):905-923.
[22]Dobrev, P., Famolari, D., Kurzke, C., et al., 2002. Device and service discovery in home networks with OSGi. IEEE Commun. Mag., 40(8):86-92.
[23]Dubey, A., Karsai, G., Mahadevan, N., 2011. A component model for hard real-time systems: CCM with ARINC-653. Softw. Pract. Exper., 41(12):1517-1550.
[24]Fang, X., Misra, S., Xue, G., et al., 2012. Smart grid—the new and improved power grid: a survey. IEEE Commun. Surv. Tutor., 14(4):944-980.
[25]Ferreira, P., Doltsinis, S., Anagnostopoulos, A., et al., 2013. A performance evaluation of industrial agents. Proc. 39th Annual Conf. of the IEEE Industrial Electronics Society, p.7404-7409.
[26]Fouquet, F., Morin, B., Fleurey, F., et al., 2012. A dynamic component model for cyber physical systems. Proc. 15th ACM Sigsoft Symp. on Component Based Software Engineering, p.135-144.
[27]Giordano, A., Spezzano, G., Vinci, A., 2016. A smart platform for large-scale cyber-physical systems. In: Guerrieri, A., Loscri, V., Rovella, A., et al. (Eds.), Management of Cyber Physical Objects in the Future Internet of Things. Springer International Publishing, Cham, Switzerland, p.115-134.
[28]Greer, C., Wollman, D.A., Prochaska, D.E., et al., 2014. NIST framework and roadmap for smart grid interoperability standards, release 3.0. Specical Publication 1108r3, US National Institute of Standards and Technology, Gaithersburg, USA.
[29]GRID4EU, 2012. Specification and Requirements. http://grid4eu.blob.core.windows.net/media-prod/6578/Grid4EU_dD1.1_Demo_1_V1.0.pdf [Accessed on Nov. 20, 2016].
[30]Gunes, V., Peter, S., Givargis, T., et al., 2014. A survey on concepts, applications, and challenges in cyber-physical systems. KSII Trans. Internet Inform. Syst., 8(12): 4242-4268.
[31]Haque, S.A., Aziz, S.M., Rahman, M., 2014. Review of cyber-physical system in healthcare. Int. J. Distrib. Sens. Netw., 2014:217415:1-217415:20.
[32]Hellbruck, H., Teubler, T., Fischer, S., 2013. Name-centric service architecture for cyber-physical systems. Proc. IEEE 6th Int. Conf. on Service-Oriented Computing and Applications, p.77-82.
[33]Hsieh, F.S., 2010. Design of reconfiguration mechanism for holonic manufacturing systems based on formal models. Eng. Appl. Artif. Intel., 23(7):1187-1199.
[34]Hu, F., Lu, Y., Vasilakos, A.V., et al., 2016. Robust cyber–physical systems: concept, models, and implementation. Fut. Gener. Comp. Syst., 56:449-475.
[35]Huang, J., Bastani, F., Yen, I.L., et al., 2009a. Extending service model to build an effective service composition framework for cyber-physical systems. Proc. IEEE Int. Conf. on Service-Oriented Computing and Applications, p.1-8.
[36]Huang, J., Bastani, F., Yen, I.L., et al., 2009b. Toward a smart cyber-physical space: a context-sensitive resource-explicit service model. Proc. 33rd Annual IEEE Int. Computer Software and Applications Conf., p.122-127.
[37]Huang, J., Bastani, F.B., Yen, I.L., et al., 2010. A framework for efficient service composition in cyber-physical systems. Proc. 5th IEEE Int. Symp. on Service Oriented System Engineering, p.291-298.
[38]Inam, R., Carlson, J., Sjödin, M., et al., 2014. Predictable integration and reuse of executable real-time components. J. Syst. Softw., 91:147-162.
[39]Jammes, F., Mensch, A., Smit, H., 2005. Service-oriented device communications using the devices profile for web services. Proc. 3rd Int. Workshop on Middleware for Pervasive and Ad-Hoc Computing, p.1-8.
[40]Jia, D., Lu, K., Wang, J., et al., 2015. A survey on platoon-based vehicular cyber-physical systems. IEEE Commun. Surv. Tutor., 18(1):263-284.
[41]Jin, X., Chun, S., Jung, J., et al., 2014. IoT service selection based on physical service model and absolute dominance relationship. Proc. IEEE 7th Int. Conf. on Service-Oriented Computing and Applications, p.65-72.
[42]Karnouskos, S., Bangemann, T., Diedrich, C., 2009. Integration of legacy devices in the future SOA-based factory. IFAC Proc. Vol., 42(4):2113-2118.
[43]Karnouskos, S., Colombo, A.W., Jammes, F., et al., 2010. Towards an architecture for service-oriented process monitoring and control. Proc. IECON 36th Annual Conf. on IEEE Industrial Electronics Society, p.1385-1391.
[44]Khaitan, S.K., McCalley, J.D., 2015. Design techniques and applications of cyberphysical systems: a survey. IEEE Syst. J., 9(2):350-365.
[45]Kim, M., Stehr, M.O., Kim, J., et al., 2013. An application framework for loosely coupled networked cyber-physical systems. Proc. IEEE/IFIP 8th Int. Conf. on Embedded and Ubiquitous Computing, p.144-153.
[46]Lee, E.A., 2008. Cyber physical systems: design challenges. Proc. 11th IEEE Symp. on Object/Component/Service-Oriented Real-Time Distributed Computing, p.363-369.
[47]Leitão, P., 2013. Towards self-organized service-oriented multi-agent systems. In: Borangiu, T., Thomas, A., Trentesaux, D. (Eds.), Service Orientation in Holonic and Multi Agent Manufacturing and Robotics. Springer Berlin Heidelberg, p.41-56.
[48]Leitão, P., Restivo, F., 2006. ADACOR: a holonic architecture for agile and adaptive manufacturing control. Comput. Ind., 57(2):121-130.
[49]Leitão, P., Marik, V., Vrba, P., 2013. Past, present, and future of industrial agent applications. IEEE Trans. Ind. Inform., 9(4):2360-2372.
[50]Lepuschitz, W., Vallee, M., Merdan, M., et al., 2009. Integration of a heterogeneous low level control in a multi-agent system for the manufacturing domain. Proc. 14th IEEE Int. Conf. on Emerging Technologies Factory Automation, p.574-581.
[51]Levendovszky, T., Dubey, A., Otte, W.R., et al., 2014. Distributed real-time managed systems: a model-driven distributed secure information architecture platform for managed embedded systems. IEEE Softw., 31(2):62-69.
[52]Li, F., Xu, J., Yu, G., 2012. A survey on event processing for CPS. In: Wang, R., Xiao, F. (Eds.), Advances in Wireless Sensor Networks. Springer Berlin Heidelberg, p.157-166.
[53]Li, Q., Qin, W., Han, B., et al., 2011. A case study on rest-style architecture for cyber-physical systems: restful smart gateway. Comput. Sci. Inform. Syst., 8(4):1317-1329.
[54]Li, R.F., Xie, Y., Li, R., et al., 2012. Survey of cyber-physical systems. J. Comput. Res. Dev., 49(6):1149-1161 (in Chinese).
[55]Lin, J., Sedigh, S., Miller, A., 2011. A semantic agent framework for cyber-physical systems. In: Elçi, A., Koné, M.T., Orgun, M.A. (Eds.), Semantic Agent Systems. Springer Berlin Heidelberg, p.189-213.
[56]Lopez, P., Medina, J.L., Drake, J.M., 2006. Real-time modelling of distributed component-based applications. Proc. 32nd EUROMICRO Conf. on Software Engineering and Advanced Applications, p.92-99.
[57]Macana, C.A., Quijano, N., Mojica-Nava, E., 2011. A survey on cyber physical energy systems and their applications on smart grids. Proc. IEEE PES Conf. on Innovative Smart Grid Technologies, p.1-7.
[58]Martin, D., Paolucci, M., McIlraith, S., et al., 2005. Bringing semantics to web services: the OWL-S approach. In: Cardoso, J., Sheth, A. (Eds.), Semantic Web Services and Web Process Composition. Springer-Verlag Berlin Heidelberg, p.26-42.
[59]Martínez, P.L., Cuevas, C., Drake, J.M., 2010. RT-D&C: deployment specification of real-time component-based applications. Proc. 36th EUROMICRO Conf. on Software Engineering and Advanced Applications, p.147-155.
[60]Martínez, P.L., Barros, L., Drake, J.M., 2013. Design of component-based real-time applications. J. Syst. Softw., 86(2):449-467.
[61]Mendes, J.M., Leitão, P., Restivo, F., et al., 2009. Service-oriented agents for collaborative industrial automation and production systems. In: Mařík, V., Strasser, T., Zoitl, A. (Eds.), Holonic and Multi-agent Systems for Manufacturing. Springer-Verlag Berlin Heidelberg, p.13-24.
[62]Mendes, J.M., Leitão, P., Restivo, F., et al., 2010. Composition of Petri nets models in service-oriented industrial automation. Proc. 8th IEEE Int. Conf. on Industrial Informatics, p.578-583.
[63]Microsoft, 2015. Smart Energy Reference Architecture Version 2.0. https://msenterprise.global.ssl.fastly.net/wordpress/ Reference_Architecture_pdf_whitepaper_2.pdf [Accessed on Nov. 20, 2016].
[64]Miller, B.A., Nixon, T., Tai, C., et al., 2001. Home networking with universal plug and play. IEEE Commun. Mag., 39(12):104-109.
[65]Monostori, L., Kadar, B., Bauernhansl, T., et al., 2016. Cyber-physical systems in manufacturing. CIRP Ann. Manuf. Techn., 65(2):621-641.
[66]Morin, B., Barais, O., Nain, G., et al., 2009. Taming dynamically adaptive systems using models and aspects. Proc. 31st Int. Conf. on Software Engineering, p.122-132.
[67]Muccini, H., Sharaf, M., Weyns, D., 2016. Self-adaptation for cyber-physical systems: a systematic literature review. Proc. 11th Int. Workshop on Software Engineering for Adaptive and Self-Managing Systems, p.75-81.
[68]Ni, Z., Kobetski, A., Axelsson, J., 2014. Design and implementation of a dynamic component model for federated AUTOSAR systems. Proc. 51st Annual Design Automation Conf., p.94:1-94:6.
[69]Nikam, S., Ingle, R., 2014. Resource provisioning algorithms for service composition in Cyber Physical Systems. Proc. Int. Conf. on Advances in Computing, Communications and Informatics, p.2797-2802.
[70]Obermaisser, R., Huber, B., 2009. The GENESYS architecture: a conceptual model for component-based distributed real-time systems. In: Lee, S., Narasimhan, P. (Eds.), Software Technologies for Embedded and Ubiquitous Systems. Springer-Verlag Berlin Heidelberg, p.296-307.
[71]Otte, W.R., Dubey, A., Karsai, G., 2014. A resilient and secure software platform and architecture for distributed spacecraft. SPIE, 9085:90850J.
[72]Pajic, M., Chernoguzov, A., Mangharam, R., 2012. Robust architectures for embedded wireless network control and actuation. ACM Trans. Embed. Comput. Syst., 11(4):82.
[73]Papazoglou, M.P., Heuvel, W.J., 2007. Service oriented architectures: approaches, technologies and research issues. VLDB J., 16(3):389-415.
[74]Park, S.O., Do, T.H., Jeong, Y.S., et al., 2013. A dynamic control middleware for cyber physical systems on an IPv6-based global network. Int. J. Commun. Syst., 26(6): 690-704.
[75]Parvin, S., Hussain, F.K., Hussain, O.K., et al., 2013. Multi-cyber framework for availability enhancement of cyber physical systems. Computing, 95(10-11):927-948.
[76]Pradhan, S., Otte, W.R., Dubey, A., et al., 2014. Towards a resilient deployment and configuration infrastructure for fractionated spacecraft. ACM SIGBED Rev., 10(4):29-32.
[77]Puttonen, J., Lobov, A., Lastra, J.L.M., 2008. An application of BPEL for service orchestration in an industrial environment. Proc. 13th IEEE Int. Conf. on Emerging Technologies and Factory Automation, p.530-537.
[78]Rajkumar, R., Lee, I., Sha, L., et al., 2010. Cyber-physical systems: the next computing revolution. Proc. 47th ACM/IEEE Design Automation Conf., p.731-736.
[79]Schirner, G., Erdogmus, D., Chowdhury, K., et al., 2013. The future of human-in-the-loop cyber-physical systems. Computer, 46(1):36-45.
[80]Seow, K.T., Dang, N.H., Lee, D.H., 2010. A collaborative multiagent taxi-dispatch system. IEEE Trans. Autom. Sci. Eng., 7(3):607-616.
[81]Sha, L., Gopalakrishnan, S., Liu, X., et al., 2008. Cyber-physical systems: a new frontier. Proc. IEEE Int. Conf. on Sensor Networks, Ubiquitous and Trustworthy Computing, p.1-9.
[82]Shi, J., Wan, J., Yan, H., et al., 2011. A survey of cyber-physical systems. Proc. Int. Conf. on Wireless Communications and Signal Processing, p.1-6.
[83]SMB Smart Grid Strategic Group, 2010. IEC Smart Grid Standardization Roadmap. http://www.iec.ch/smartgrid/downloads/sg3_roadmap.pdf [Accessed on Nov. 20, 2016].
[84]Soulier, P., Li, D., Williams, J.R., 2015. A survey of language-based approaches to Cyber-Physical and embedded system development. Tsinghua Sci. Technol., 20(2):130-141.
[85]Srbljic, S., Skvorc, D., Popovic, M., 2012. Programming languages for end-user personalization of cyber-physical systems. Automatika, 53(3):294-310.
[86]Stojmenovic, I., 2014. Machine-to-machine communications with in-network data aggregation, processing, and actuation for large-scale cyber-physical systems. IEEE IOT J., 1(2):122-128.
[87]Tan, Y., Vuran, M.C., Goddard, S., 2009. Spatio-temporal event model for cyber-physical systems. Proc. 29th IEEE Int. Conf. on Distributed Computing Systems Workshops, p.44-50.
[88]Valls, M.G., Lopez, I.R., Villar, L.F., 2013. iLand: an enhanced middleware for real-time reconfiguration of service oriented distributed real-time systems. IEEE Trans. Ind. Inform., 9(1):228-236.
[89]Vegh, L., Miclea, L., 2016. Secure and efficient communication in cyber-physical systems through cryptography and complex event processing. Proc. Int. Conf. on Communications, p.273-276.
[90]Vicaire, P.A., Xie, Z., Hoque, E., et al., 2010. Physicalnet: a generic framework for managing and programming across pervasive computing networks. Proc. 16th IEEE Real-Time and Embedded Technology and Applications Symp., p.269-278.
[91]Vicaire, P.A., Hoque, E., Xie, Z., et al., 2012. Bundle: a group-based programming abstraction for cyber-physical systems. IEEE Trans. Ind. Inform., 8(2):379-392.
[92]Vrba, P., Radakovič, M., Obitko, M., et al., 2011a. Semantic technologies: latest advances in agent-based manufacturing control systems. Int. J. Prod. Res., 49(5):1483-1496.
[93]Vrba, P., Tichý, P., Mařík, V., et al., 2011b. Rockwell automation’s holonic and multiagent control systems compendium. IEEE Trans. Syst. Man Cybern. C, 41(1):14-30.
[94]Vrba, P., Mařík, V., Siano, P., et al., 2014. A review of agent and service-oriented concepts applied to intelligent energy systems. IEEE Trans. Ind. Inform., 10(3):1890-1903.
[95]Wan, J., Yan, H., Suo, H., et al., 2011. Advances in cyber-physical systems research. KSII Trans. Internet Inform., 5(11):1891-1908.
[96]Wan, K., Alagar, V., Dong, Y., 2014. Specifying resource-centric services in cyber physical systems. In: Yang, G.C., Ao, S.I., Huang, X., et al. (Eds.), Transactions on Engineering Technologies. Springer Netherlands, Dordrecht, the Netherland, p.83-97.
[97]Wang, F.Y., 2008. Toward a revolution in transportation operations: AI for complex systems. IEEE Intell. Syst., 23(6): 8-13.
[98]Wang, T., Cheng, L., Zheng, K., 2012. Automatic and effective service provision with context-aware service composition mechanism in cyber-physical systems. Adv. Inform. Sci. Serv. Sci., 4(11):151-160.
[99]Wang, Z.J., Xie, L.L., 2011. Cyber-physical systems: a survey. Acta Autom. Sin., 37(10):1157-1166 (in Chinese).
[100]Woo, H., Yi, J., Browne, J.C., et al., 2008. Design and development methodology for resilient cyber-physical systems. Proc. 28th Int. Conf. on Distributed Computing Systems Workshops, p.525-528.
[101]Wu, G., Sun, J., Chen, J., 2016. A survey on the security of cyber-physical systems. J. Contr. Theory Technol., 14(1):2-10.
[102]Wu, L., Kaiser, G., 2012. An autonomic reliability improvement system for cyber-physical systems. Proc. IEEE 14th Int. Symp. on High-Assurance Systems Engineering, p.56-61.
[103]Xiao, K., Ren, S., Kwiat, K., 2008. Retrofitting cyber physical systems for survivability through external coordination. Proc. 41st Annual Hawaii Int. Conf. on System Sciences, p.465-465.
[104]Zhao, C., Dong, W., Qi, Z., 2010. Active monitoring for control systems under anticipatory semantics. Proc. 10th Int. Conf. on Quality Software, p.318-325.
[105]Zhou, X.S., Yang, Y.L., Yang, G., 2014. Modeling methods for dynamic behaviors of cyber-physical system. Chin. J. Comp. 37(6):1411-1423 (in Chinese).
[106]Zhu, W., Zhou, G., Yen, I.L., et al., 2015. A PT-SOA model for CPS/IoT services. Proc. IEEE Int. Conf. on Web Services, p.647-654.
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