Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595184
R. Grimm, B. Bershad
The recent trend towards dynamically extensible systems, such as Java, SPIN or VINO, promises more powerful and flexible systems. At the same time, the impact of extensibility on overall system security and, specifically, on access control is still ill understood, and protection mechanisms in these extensible systems are rudimentary at best. We identify the structure of extensible systems as it relates to system security and postulate an initial model for access control. This model extends the discretionary access control of traditional operating systems to encompass extensions and, by using ideas explored by the security community, introduces a notion of mandatory access control. While a new access control model does not address all aspects of system security, we believe that it can serve as a solid foundation for developing a fully featured and flexible security model for extensible systems.
{"title":"Security for extensible systems","authors":"R. Grimm, B. Bershad","doi":"10.1109/HOTOS.1997.595184","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595184","url":null,"abstract":"The recent trend towards dynamically extensible systems, such as Java, SPIN or VINO, promises more powerful and flexible systems. At the same time, the impact of extensibility on overall system security and, specifically, on access control is still ill understood, and protection mechanisms in these extensible systems are rudimentary at best. We identify the structure of extensible systems as it relates to system security and postulate an initial model for access control. This model extends the discretionary access control of traditional operating systems to encompass extensions and, by using ideas explored by the security community, introduces a notion of mandatory access control. While a new access control model does not address all aspects of system security, we believe that it can serve as a solid foundation for developing a fully featured and flexible security model for extensible systems.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"431 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115613039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595187
Paul J Leach, C. Weider
As the Internet continues to grow exponentially, locating desired information becomes more difficult. Centralized approaches to the problem may prove unable to cope with this growth, and existing distributed ones do not scale well either, so it would be wise to investigate alternatives. One alternative is 'query routing', a technology which uses compressed indices from multiple sites to 'route' queries to where they may be able to be fulfilled. By using a referral model for the clients, it should be possible to provide a service which scales for both clients and servers. Server scaling is achieved by index compression along several novel axes. Allowing the generation of false positives permits the use of techniques which have higher compression. We have been able to add techniques from distributed naming systems such as DNS to traditional indexing based on flat sets of attribute value pairs. We have implemented a prototype that incorporates several of these techniques.
{"title":"Query routing: applying systems thinking to Internet search","authors":"Paul J Leach, C. Weider","doi":"10.1109/HOTOS.1997.595187","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595187","url":null,"abstract":"As the Internet continues to grow exponentially, locating desired information becomes more difficult. Centralized approaches to the problem may prove unable to cope with this growth, and existing distributed ones do not scale well either, so it would be wise to investigate alternatives. One alternative is 'query routing', a technology which uses compressed indices from multiple sites to 'route' queries to where they may be able to be fulfilled. By using a referral model for the clients, it should be possible to provide a service which scales for both clients and servers. Server scaling is achieved by index compression along several novel axes. Allowing the generation of false positives permits the use of techniques which have higher compression. We have been able to add techniques from distributed naming systems such as DNS to traditional indexing based on flat sets of attribute value pairs. We have implemented a prototype that incorporates several of these techniques.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124836439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595174
B. Fleisch
IBM's adoption of operating system personalities was one of the most publicized issues in operating systems design. The basic premise of Workplace OS work was: (1) IBM would adopt and improve the CMU Mach 3.0 microkernel for use on PDAs, the desktop and massively parallel machines, and (2) that several operating system personalities would execute on the microkernel platform concurrently. This architecture would provide users with the best worlds as they switch between applications written for different operating systems. IBM would also benefit from significant cost savings by having one common platform for all product lines. IBM's plans for use of the microkernel and multiple-personalities, as a unifying mechanism for a widely diverse set of hardware products, have failed. We examine why IBM's microkernel and multipersonality system was not successful from a technical and business standpoint. We also discuss Power Personal systems, which were introduced during these radical software changes and then later abandoned.
{"title":"The failure of personalities to generalize","authors":"B. Fleisch","doi":"10.1109/HOTOS.1997.595174","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595174","url":null,"abstract":"IBM's adoption of operating system personalities was one of the most publicized issues in operating systems design. The basic premise of Workplace OS work was: (1) IBM would adopt and improve the CMU Mach 3.0 microkernel for use on PDAs, the desktop and massively parallel machines, and (2) that several operating system personalities would execute on the microkernel platform concurrently. This architecture would provide users with the best worlds as they switch between applications written for different operating systems. IBM would also benefit from significant cost savings by having one common platform for all product lines. IBM's plans for use of the microkernel and multiple-personalities, as a unifying mechanism for a widely diverse set of hardware products, have failed. We examine why IBM's microkernel and multipersonality system was not successful from a technical and business standpoint. We also discuss Power Personal systems, which were introduced during these radical software changes and then later abandoned.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123363085","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595176
Patrick Tullmann, J. Turner, J. McCorquodale, Jay Lepreau, Ajaya Chitturi, Godmar Back
The formal methods community has long known about the need to formally analyze concurrent software, but the operating systems (OS) community has been slow to adopt such methods. The foremost reasons for this are the cultural and knowledge gaps between formalists and OS hackers, fostered by three beliefs: inaccessibility of the tools, the disabling gap between the validated model and actual implementation, and the intractable size of OSs. In this paper, we show these beliefs to be untrue for appropriately structured OSs. We applied formal methods to verify properties of the implementation of the Fluke microkernel's IPC (interprocess communication) subsystem, a major component of the kernel. In particular, we have verified, in many scenarios, certain liveness properties and lack of deadlock, with results that apply to both SMP (scalable multiprocessor) and uniprocessor environments. The SPIN model checker provided an exhaustive concurrency analysis of the IPC subsystem, unattainable through traditional OS testing methods. SPIN is easily accessible to programmers inexperienced with formal methods. We present our results as a starting point for a more comprehensive inclusion of formal methods in practical OS development.
{"title":"Formal methods: a practical tool for OS implementors","authors":"Patrick Tullmann, J. Turner, J. McCorquodale, Jay Lepreau, Ajaya Chitturi, Godmar Back","doi":"10.1109/HOTOS.1997.595176","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595176","url":null,"abstract":"The formal methods community has long known about the need to formally analyze concurrent software, but the operating systems (OS) community has been slow to adopt such methods. The foremost reasons for this are the cultural and knowledge gaps between formalists and OS hackers, fostered by three beliefs: inaccessibility of the tools, the disabling gap between the validated model and actual implementation, and the intractable size of OSs. In this paper, we show these beliefs to be untrue for appropriately structured OSs. We applied formal methods to verify properties of the implementation of the Fluke microkernel's IPC (interprocess communication) subsystem, a major component of the kernel. In particular, we have verified, in many scenarios, certain liveness properties and lack of deadlock, with results that apply to both SMP (scalable multiprocessor) and uniprocessor environments. The SPIN model checker provided an exhaustive concurrency analysis of the IPC subsystem, unattainable through traditional OS testing methods. SPIN is easily accessible to programmers inexperienced with formal methods. We present our results as a starting point for a more comprehensive inclusion of formal methods in practical OS development.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134266677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595180
M. Auslander, H. Franke, Benjamin Gamsa, O. Krieger, M. Stumm
There has been a great deal of interest in recent years in developing operating systems that can be customized to meet the performance and functionality needs of particular applications while being extensible to support new policies, new implementations and new interfaces. We describe a structuring technique, called building-block composition, that we are employing for this purpose. The customizability that this technique provides to untrusted applications is, while large, less than that provided by some other techniques. However, it results in a more extensible and maintainable system, is easier for untrusted applications to use, and provides a better foundation for overall improved performance, particularly for multiprocessors.
{"title":"Customization lite [operating systems]","authors":"M. Auslander, H. Franke, Benjamin Gamsa, O. Krieger, M. Stumm","doi":"10.1109/HOTOS.1997.595180","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595180","url":null,"abstract":"There has been a great deal of interest in recent years in developing operating systems that can be customized to meet the performance and functionality needs of particular applications while being extensible to support new policies, new implementations and new interfaces. We describe a structuring technique, called building-block composition, that we are employing for this purpose. The customizability that this technique provides to untrusted applications is, while large, less than that provided by some other techniques. However, it results in a more extensible and maintainable system, is easier for untrusted applications to use, and provides a better foundation for overall improved performance, particularly for multiprocessors.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128122977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595185
S. Forrest, Anil Somayaji, D. Ackley
Diversity is an important source of robustness in biological systems. Computers, by contrast, are notable for their lack of diversity. Although homogeneous systems have many advantages, the beneficial effects of diversity in computing systems have been overlooked, specifically in the area of computer security. Several methods of achieving software diversity are discussed based on randomizations that respect the specified behavior of the program. Such randomization could potentially increase the robustness of software systems with minimal impact on convenience, usability, and efficiency. Randomization of the amount of memory allocated on a stack frame is shown to disrupt a simple buffer overflow attack.
{"title":"Building diverse computer systems","authors":"S. Forrest, Anil Somayaji, D. Ackley","doi":"10.1109/HOTOS.1997.595185","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595185","url":null,"abstract":"Diversity is an important source of robustness in biological systems. Computers, by contrast, are notable for their lack of diversity. Although homogeneous systems have many advantages, the beneficial effects of diversity in computing systems have been overlooked, specifically in the area of computer security. Several methods of achieving software diversity are discussed based on randomizations that respect the specified behavior of the program. Such randomization could potentially increase the robustness of software systems with minimal impact on convenience, usability, and efficiency. Randomization of the amount of memory allocated on a stack frame is shown to disrupt a simple buffer overflow attack.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132198079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595186
J. Liedtke, N. Islam, T. Jaeger
A goal of World Wide Web operating systems (WebOSes) is to enable clients to download executable content from servers connected to the World Wide Web (WWW). This will make applications more easily available to clients, but some of these applications may be malicious. Thus, a WebOS must be able to control the downloaded content's behavior. We examine a specific type of malicious activity: denial of service attacks using legal system operations. A denial of service attack occurs when an attacker prevents other users from performing their authorized operations. Even when the attacker may not be able to perform such operations. Current systems either do little to prevent denial of service attacks or have a limited scope of prevention of such attacks. For a WebOS, however, the ability to prevent denial of service should be an integral part of the system. We are developing a WebOS using the L4 /spl mu/ kernel as its substrate. We evaluate L4 as a basis of a system that can prevent denial of service attacks. In particular, we identify the /spl mu/ kernel related resources which are subject to denial of service attacks and define /spl mu/ kernel mechanisms to defend against such attacks. Our analysis demonstrates that system resource utilization can be managed by trusted user level servers to prevent denial of service attacks on such resources.
{"title":"Preventing denial-of-service attacks on a /spl mu/-kernel for WebOSes","authors":"J. Liedtke, N. Islam, T. Jaeger","doi":"10.1109/HOTOS.1997.595186","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595186","url":null,"abstract":"A goal of World Wide Web operating systems (WebOSes) is to enable clients to download executable content from servers connected to the World Wide Web (WWW). This will make applications more easily available to clients, but some of these applications may be malicious. Thus, a WebOS must be able to control the downloaded content's behavior. We examine a specific type of malicious activity: denial of service attacks using legal system operations. A denial of service attack occurs when an attacker prevents other users from performing their authorized operations. Even when the attacker may not be able to perform such operations. Current systems either do little to prevent denial of service attacks or have a limited scope of prevention of such attacks. For a WebOS, however, the ability to prevent denial of service should be an integral part of the system. We are developing a WebOS using the L4 /spl mu/ kernel as its substrate. We evaluate L4 as a basis of a system that can prevent denial of service attacks. In particular, we identify the /spl mu/ kernel related resources which are subject to denial of service attacks and define /spl mu/ kernel mechanisms to defend against such attacks. Our analysis demonstrates that system resource utilization can be managed by trusted user level servers to prevent denial of service attacks on such resources.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115182221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595179
P. Druschel, Vivek S. Pai, W. Zwaenepoel
Argues that ongoing research in extensible kernels largely fails to address the real challenges facing the operating systems (OS) community. Instead, these efforts have become entangled in trying to solve the safety problems that extensibility itself introduces into OS design. We propose a pragmatic approach to extensibility, where kernel extensions are used in experimental settings to evaluate and develop OS enhancements for demanding applications. Once developed and well understood, these enhancements are then migrated into the base OS for production use. This approach obviates the need for guaranteeing the safety of kernel extensions, allowing the OS research community to re-focus on the real challenges in OS design and implementation. To provide a concrete example of this approach, we analyze the techniques used in experimental HTTP servers to show how proper application design combined with generic enhancements to OSs can provide the same benefits without requiring application-specific kernel extensions.
{"title":"Extensible kernels are leading OS research astray","authors":"P. Druschel, Vivek S. Pai, W. Zwaenepoel","doi":"10.1109/HOTOS.1997.595179","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595179","url":null,"abstract":"Argues that ongoing research in extensible kernels largely fails to address the real challenges facing the operating systems (OS) community. Instead, these efforts have become entangled in trying to solve the safety problems that extensibility itself introduces into OS design. We propose a pragmatic approach to extensibility, where kernel extensions are used in experimental settings to evaluate and develop OS enhancements for demanding applications. Once developed and well understood, these enhancements are then migrated into the base OS for production use. This approach obviates the need for guaranteeing the safety of kernel extensions, allowing the OS research community to re-focus on the real challenges in OS design and implementation. To provide a concrete example of this approach, we analyze the techniques used in experimental HTTP servers to show how proper application design combined with generic enhancements to OSs can provide the same benefits without requiring application-specific kernel extensions.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129094152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595191
W. Bolosky, Richard Draves, Robert P. Fitzgerald, C. Fraser, Michael B. Jones, Todd B. Knoblock, R. Rashid
We believe it is time to reexamine the operating system's role in computing. Operating systems exist to create an environment in which compelling applications come to life. They do that by providing abstractions built on the services provided by hardware. We argue that advances in hardware and networking technology enable a new kind of operating system to support tomorrow's applications. Such an operating system would raise the level of abstraction for developers and users, so that individual computers, file systems, and networks become unimportant to most computations in the same way that processor registers, disk sectors, and physical pages are today.
{"title":"Operating system directions for the next Millennium","authors":"W. Bolosky, Richard Draves, Robert P. Fitzgerald, C. Fraser, Michael B. Jones, Todd B. Knoblock, R. Rashid","doi":"10.1109/HOTOS.1997.595191","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595191","url":null,"abstract":"We believe it is time to reexamine the operating system's role in computing. Operating systems exist to create an environment in which compelling applications come to life. They do that by providing abstractions built on the services provided by hardware. We argue that advances in hardware and networking technology enable a new kind of operating system to support tomorrow's applications. Such an operating system would raise the level of abstraction for developers and users, so that individual computers, file systems, and networks become unimportant to most computations in the same way that processor registers, disk sectors, and physical pages are today.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133041139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1997-05-05DOI: 10.1109/HOTOS.1997.595196
M. Satyanarayanan, Brian D. Noble
We put forth the view that trace modulation is an indispensable technique for building and evaluating mobile computing systems. The essence of our solution is transparent, real-time, trace-driven emulation of a target network. Although conceptually simple, trace modulation strikes an attractive balance between the conflicting demands of realism, ease-of-use, and reproducibility. It provides three important benefits. First, it allows control of the complexity of the network environment to which mobile software is exposed. Second, it enables mobile clients to be subjected to reproducible yet realistic network performance. Third, it allows easy exploration of a mobile system in the context of hypothetical mobility patterns and network infrastructures. These benefits suggest that trace modulation will play a central role in the development of future mobile computing systems.
{"title":"The role of trace modulation in building mobile computing systems","authors":"M. Satyanarayanan, Brian D. Noble","doi":"10.1109/HOTOS.1997.595196","DOIUrl":"https://doi.org/10.1109/HOTOS.1997.595196","url":null,"abstract":"We put forth the view that trace modulation is an indispensable technique for building and evaluating mobile computing systems. The essence of our solution is transparent, real-time, trace-driven emulation of a target network. Although conceptually simple, trace modulation strikes an attractive balance between the conflicting demands of realism, ease-of-use, and reproducibility. It provides three important benefits. First, it allows control of the complexity of the network environment to which mobile software is exposed. Second, it enables mobile clients to be subjected to reproducible yet realistic network performance. Third, it allows easy exploration of a mobile system in the context of hypothetical mobility patterns and network infrastructures. These benefits suggest that trace modulation will play a central role in the development of future mobile computing systems.","PeriodicalId":176246,"journal":{"name":"Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No.97TB100133)","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126813410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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