Pub Date : 1995-12-01DOI: 10.1088/0967-1846/2/4/002
Toshio Hirotsu, H. Fujii, M. Tokoro
We propose an extended concurrent object model for distributed multiuser systems called the multiversion concurrent object (MCO). The original concurrent object model is simple because it excludes internal concurrency, but this may cause long blocking on its execution during message sending and external device accesses. Thus, these blockings may decrease system performance. We introduce a multiversion mechanism to the original concurrent object model. Each MCO makes a copy of its own state, which is called a version, for executing a method that is not interleaved with other similar copies during execution. The results from concurrent execution are merged upon termination of each method. The MCO simplifies programming, since synchronization statements are not required inside its methods. Using this model for shared objects, we can construct a system in which each user can work freely without suffering from other user`s unexpected actions. We present a prototype implementation of MCO and some performance evaluations.
{"title":"A multiversion mechanism for intra-object concurrency","authors":"Toshio Hirotsu, H. Fujii, M. Tokoro","doi":"10.1088/0967-1846/2/4/002","DOIUrl":"https://doi.org/10.1088/0967-1846/2/4/002","url":null,"abstract":"We propose an extended concurrent object model for distributed multiuser systems called the multiversion concurrent object (MCO). The original concurrent object model is simple because it excludes internal concurrency, but this may cause long blocking on its execution during message sending and external device accesses. Thus, these blockings may decrease system performance. We introduce a multiversion mechanism to the original concurrent object model. Each MCO makes a copy of its own state, which is called a version, for executing a method that is not interleaved with other similar copies during execution. The results from concurrent execution are merged upon termination of each method. The MCO simplifies programming, since synchronization statements are not required inside its methods. Using this model for shared objects, we can construct a system in which each user can work freely without suffering from other user`s unexpected actions. We present a prototype implementation of MCO and some performance evaluations.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123591654","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 : 1995-09-01DOI: 10.1088/0967-1846/2/3/003
D. Huizinga, K. A. Heflinger
This paper identifies design requirements of system-level support for mobile computing in small form-factor battery-powered portable computers and describes their implementation in DOC (Disconnected Operation Cache). DOC is a three-level client caching system designed and implemented to allow mobile clients to transition between connected, partially disconnected and fully disconnected modes of operation with minimal user involvement. Implemented for notebook computers, DOC addresses not only typical issues of mobile elements such as resource scarcity and fluctuations in service quality but also deals with the pitfalls of MS-DOS, the operating system which prevails in the commercial notebook market. Our experiments performed in the software engineering environment of AST Research indicate not only considerable performance gains for connected and partially disconnected modes of DOC, but also the successful operation of the disconnected mode.
{"title":"DOC-a file system cache to support mobile computers","authors":"D. Huizinga, K. A. Heflinger","doi":"10.1088/0967-1846/2/3/003","DOIUrl":"https://doi.org/10.1088/0967-1846/2/3/003","url":null,"abstract":"This paper identifies design requirements of system-level support for mobile computing in small form-factor battery-powered portable computers and describes their implementation in DOC (Disconnected Operation Cache). DOC is a three-level client caching system designed and implemented to allow mobile clients to transition between connected, partially disconnected and fully disconnected modes of operation with minimal user involvement. Implemented for notebook computers, DOC addresses not only typical issues of mobile elements such as resource scarcity and fluctuations in service quality but also deals with the pitfalls of MS-DOS, the operating system which prevails in the commercial notebook market. Our experiments performed in the software engineering environment of AST Research indicate not only considerable performance gains for connected and partially disconnected modes of DOC, but also the successful operation of the disconnected mode.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126965344","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 : 1995-09-01DOI: 10.1088/0967-1846/2/3/001
A. Schill, Sascha Kümmel
With the rapid development of mobile computer systems and mobile communication infrastructures, a broad field of distributed mobile computing is enabled. The paper first discusses these developments in closer detail and summarizes the resulting requirements concerning adequate software support. An application scenario of the service engineering area illustrates specific aspects including bandwidth and location management, dynamic configuration, resource heterogeneity, disconnection, and security. Based on these considerations, a generic software support platform for distributed mobile computing is derived. It addresses several of these aspects by providing application-independent and reusable support services. In particular, it offers a framework for organizing distributed mobile applications into manageable domains, it equips mobile stations with enhanced functionality for location, resource and bandwidth management, and it uses industry standard RPC communication facilities for enhanced portability. The design, implementation and use of the support platform is illustrated based on a specific part of the application, a mobile multimedia e-mail system. Experiences and implementation aspects in this context are particularly emphasized.
{"title":"Design and implementation of a support platform for distributed mobile computing","authors":"A. Schill, Sascha Kümmel","doi":"10.1088/0967-1846/2/3/001","DOIUrl":"https://doi.org/10.1088/0967-1846/2/3/001","url":null,"abstract":"With the rapid development of mobile computer systems and mobile communication infrastructures, a broad field of distributed mobile computing is enabled. The paper first discusses these developments in closer detail and summarizes the resulting requirements concerning adequate software support. An application scenario of the service engineering area illustrates specific aspects including bandwidth and location management, dynamic configuration, resource heterogeneity, disconnection, and security. Based on these considerations, a generic software support platform for distributed mobile computing is derived. It addresses several of these aspects by providing application-independent and reusable support services. In particular, it offers a framework for organizing distributed mobile applications into manageable domains, it equips mobile stations with enhanced functionality for location, resource and bandwidth management, and it uses industry standard RPC communication facilities for enhanced portability. The design, implementation and use of the support platform is illustrated based on a specific part of the application, a mobile multimedia e-mail system. Experiences and implementation aspects in this context are particularly emphasized.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133700457","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 : 1995-09-01DOI: 10.1088/0967-1846/2/3/005
A. Dix
The design of effective collaborative applications on mobile platforms has many problems. Wireless networks are fast enough that one aspires to true interactive applications, but too slow for much real-time feedback. This is exacerbated by the variability due to interference and broken connections. Mobile computing using wireless communications thus sits in a grey area between different styles of interaction. This paper examines these problems using concepts developed to understand general user interaction and computer-supported cooperative work. In particular, it will focus on the conflict between feedback for each user, awareness and feedthrough of the effect of each users actions to others, and the consistency of shared information during periods of disconnection.
{"title":"Cooperation without (reliable) communication: Interfaces for mobile applications","authors":"A. Dix","doi":"10.1088/0967-1846/2/3/005","DOIUrl":"https://doi.org/10.1088/0967-1846/2/3/005","url":null,"abstract":"The design of effective collaborative applications on mobile platforms has many problems. Wireless networks are fast enough that one aspires to true interactive applications, but too slow for much real-time feedback. This is exacerbated by the variability due to interference and broken connections. Mobile computing using wireless communications thus sits in a grey area between different styles of interaction. This paper examines these problems using concepts developed to understand general user interaction and computer-supported cooperative work. In particular, it will focus on the conflict between feedback for each user, awareness and feedthrough of the effect of each users actions to others, and the consistency of shared information during periods of disconnection.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132720957","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 : 1995-09-01DOI: 10.1088/0967-1846/2/3/002
N. Davies, G. Blair, K. Cheverst, A. Friday
Significant advances have been made in recent years in tackling the problem of heterogeneity in distributed systems with ISO/ITU-T standards for a Reference Model for Open Distributed Processing (RM-ODP) now approaching international agreement. It is important, however, that such standards are responsive to new developments in computer and communications technologies. This paper reports on experiences of applying RM-ODP technology and mobile communications in supporting field workers in the electricity industry. The results of the study show that the framework provided by RM-ODP offers a strong basis for the development of mobile applications. Particular benefits are gained from the object-oriented modelling approach, the model of selective distribution transparency and the concept of QoS-managed bindings in RM-ODP. However, our experiences indicate that care must be taken in the development of RM-ODP compliant platforms particularly with respect to the communications infrastructure.
{"title":"Experiences of using RM-ODP to build advanced mobile applications","authors":"N. Davies, G. Blair, K. Cheverst, A. Friday","doi":"10.1088/0967-1846/2/3/002","DOIUrl":"https://doi.org/10.1088/0967-1846/2/3/002","url":null,"abstract":"Significant advances have been made in recent years in tackling the problem of heterogeneity in distributed systems with ISO/ITU-T standards for a Reference Model for Open Distributed Processing (RM-ODP) now approaching international agreement. It is important, however, that such standards are responsive to new developments in computer and communications technologies. This paper reports on experiences of applying RM-ODP technology and mobile communications in supporting field workers in the electricity industry. The results of the study show that the framework provided by RM-ODP offers a strong basis for the development of mobile applications. Particular benefits are gained from the object-oriented modelling approach, the model of selective distribution transparency and the concept of QoS-managed bindings in RM-ODP. However, our experiences indicate that care must be taken in the development of RM-ODP compliant platforms particularly with respect to the communications infrastructure.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128281410","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 : 1995-09-01DOI: 10.1088/0967-1846/2/3/004
T. Kirste
Global information management systems based on the vision of the 'docuverse'-such as the World-Wide Web (WWW)-show that on-line access to vast amounts of distributed information is possible not only for the expert, but also for the end user. At the same time, the availability of affordable mid- and long-range wireless data communication services, based, e.g., on cellular phone technology, has put the vision of ubiquitous mobile information access within the reach of viable projects. It is now an interesting challenge to combine both concepts into a system model granting everyone ubiquitous access to the global information repository. However, problems such as low bandwidth and limited resources make this a non-trivial task. This paper describes MIS/O, an experimental mobile information system based on wireless data communication which has been developed at the Computer Graphics Center during 1994. MIS/O and its underlying concepts address the above mentioned problem areas by introducing a fragmented object model. This model provides the necessary mechanisms for a (partial) migration of object behaviour to the mobile system-acting as an intelligent data terminal-at runtime. In addition to conventional caching and compression techniques, this is required for coping with intrinsic system limitations and low communication bandwidth in an environment with a virtually unlimited number of information types and services such as the docuverse.
{"title":"An infrastructure for mobile information systems based on a fragmented object model","authors":"T. Kirste","doi":"10.1088/0967-1846/2/3/004","DOIUrl":"https://doi.org/10.1088/0967-1846/2/3/004","url":null,"abstract":"Global information management systems based on the vision of the 'docuverse'-such as the World-Wide Web (WWW)-show that on-line access to vast amounts of distributed information is possible not only for the expert, but also for the end user. At the same time, the availability of affordable mid- and long-range wireless data communication services, based, e.g., on cellular phone technology, has put the vision of ubiquitous mobile information access within the reach of viable projects. It is now an interesting challenge to combine both concepts into a system model granting everyone ubiquitous access to the global information repository. However, problems such as low bandwidth and limited resources make this a non-trivial task. This paper describes MIS/O, an experimental mobile information system based on wireless data communication which has been developed at the Computer Graphics Center during 1994. MIS/O and its underlying concepts address the above mentioned problem areas by introducing a fragmented object model. This model provides the necessary mechanisms for a (partial) migration of object behaviour to the mobile system-acting as an intelligent data terminal-at runtime. In addition to conventional caching and compression techniques, this is required for coping with intrinsic system limitations and low communication bandwidth in an environment with a virtually unlimited number of information types and services such as the docuverse.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133986580","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 : 1995-06-01DOI: 10.1088/0967-1846/2/2/005
M. Riveill
This paper presents the integration of a concurrency control mechanism in class-based languages. Synchronization constraints are expressed as separate control clauses and are factorized for a class of objects. Interference of this mechanism with inheritance and transactions is examined and solutions are proposed. This paper addresses language and system issues: canonical examples of synchronized objects are provided and an implementation of the mechanism is outlined.
{"title":"Synchronizing shared objects","authors":"M. Riveill","doi":"10.1088/0967-1846/2/2/005","DOIUrl":"https://doi.org/10.1088/0967-1846/2/2/005","url":null,"abstract":"This paper presents the integration of a concurrency control mechanism in class-based languages. Synchronization constraints are expressed as separate control clauses and are factorized for a class of objects. Interference of this mechanism with inheritance and transactions is examined and solutions are proposed. This paper addresses language and system issues: canonical examples of synchronized objects are provided and an implementation of the mechanism is outlined.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121697946","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 : 1995-06-01DOI: 10.1088/0967-1846/2/2/002
A. Berry
Maintenance of causality information in distributed systems has previously been implemented in the communications infrastructure with the focus on providing reliability and availability for distributed services. While this approach has a number of advantages, moving causality information up into the view and control of the application programmer is useful, and in some cases, preferable. In an experiment at the University of Queensland, libraries to support application-level maintenance of causality information have been implemented. The libraries allow the collection and use of causality information under programmer control, supplying a basis for making causal dependency information available for application management and troubleshooting. The libraries are also unique in supporting existing distributed systems based on the remote procedure call paradigm. This paper describes the underlying theory of causality, and the design and implementation of the libraries. An event reporting service example is used to motivate the approach, and a number of previously unresolved practical problems are addressed in the design process.
分布式系统中因果关系信息的维护以前是在通信基础设施中实现的，重点是为分布式服务提供可靠性和可用性。虽然这种方法有许多优点，但将因果关系信息向上移动到应用程序程序员的视图和控制中是有用的，并且在某些情况下是更可取的。在昆士兰大学(University of Queensland)的一项实验中，已经实现了支持应用级因果关系信息维护的图书馆。这些库允许在程序员控制下收集和使用因果关系信息，为应用程序管理和故障排除提供因果依赖信息提供基础。这些库在支持基于远程过程调用范例的现有分布式系统方面也是独一无二的。本文描述了因果关系的基本理论，以及库的设计和实现。使用事件报告服务示例来激励该方法，并且在设计过程中解决了许多以前未解决的实际问题。
{"title":"An application-level implementation of causal timestamps and causal ordering","authors":"A. Berry","doi":"10.1088/0967-1846/2/2/002","DOIUrl":"https://doi.org/10.1088/0967-1846/2/2/002","url":null,"abstract":"Maintenance of causality information in distributed systems has previously been implemented in the communications infrastructure with the focus on providing reliability and availability for distributed services. While this approach has a number of advantages, moving causality information up into the view and control of the application programmer is useful, and in some cases, preferable. In an experiment at the University of Queensland, libraries to support application-level maintenance of causality information have been implemented. The libraries allow the collection and use of causality information under programmer control, supplying a basis for making causal dependency information available for application management and troubleshooting. The libraries are also unique in supporting existing distributed systems based on the remote procedure call paradigm. This paper describes the underlying theory of causality, and the design and implementation of the libraries. An event reporting service example is used to motivate the approach, and a number of previously unresolved practical problems are addressed in the design process.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114669875","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 : 1995-06-01DOI: 10.1088/0967-1846/2/2/001
C. Baradel, Y. Eychenne, L. Junot, B. Kohen, M. Simatic
Large and dependable process control and supervision systems are a key component of today's integrated computer manufacturing. These systems must offer various levels of quality of service such as scalability, distribution, fault-tolerance and on-line maintainability. This paper presents how the concept of object groups and process groups have been exploited to meet this challenge. Object groups extend the process group functionalities with an object naming service, a trap in the object messaging for sending messages on the network transparently, and a dispatcher to retrieve the object to which the message received on the network is addressed. The process group concept provides consistent distributed data due to the use of ordered reliable multicasts and group membership management.
{"title":"Fault-tolerance and on-line maintainability in a process control supervision system","authors":"C. Baradel, Y. Eychenne, L. Junot, B. Kohen, M. Simatic","doi":"10.1088/0967-1846/2/2/001","DOIUrl":"https://doi.org/10.1088/0967-1846/2/2/001","url":null,"abstract":"Large and dependable process control and supervision systems are a key component of today's integrated computer manufacturing. These systems must offer various levels of quality of service such as scalability, distribution, fault-tolerance and on-line maintainability. This paper presents how the concept of object groups and process groups have been exploited to meet this challenge. Object groups extend the process group functionalities with an object naming service, a trap in the object messaging for sending messages on the network transparently, and a dispatcher to retrieve the object to which the message received on the network is addressed. The process group concept provides consistent distributed data due to the use of ordered reliable multicasts and group membership management.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123481806","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 : 1995-06-01DOI: 10.1088/0967-1846/2/2/003
Y. Ni, A. Goscinski
In this paper a new and original name evaluation method of attributed names is proposed and elaborated on. This method allows an attributed name to be presented in a non-hierarchical fashion and to be evaluated using a hierarchical approach. A three-level name model that supports attributed names for objects in a distributed system and the structure of naming contexts which bind attributed names onto objects are presented. The naming contexts are represented intuitively with a context-graph. To be able to meet the requirements generated from the name service semantics, a name evaluation model suitable for different name services, i.e. the conventional service, the selection service and the enquiry service has been developed. This model allows the name evaluation to be implemented efficiently. Moreover, to achieve the effectiveness and the efficiency in the implementation of the name evaluation, we have developed a set of algorithms, each of which is for a particular name service.
{"title":"Evaluation of attributed names","authors":"Y. Ni, A. Goscinski","doi":"10.1088/0967-1846/2/2/003","DOIUrl":"https://doi.org/10.1088/0967-1846/2/2/003","url":null,"abstract":"In this paper a new and original name evaluation method of attributed names is proposed and elaborated on. This method allows an attributed name to be presented in a non-hierarchical fashion and to be evaluated using a hierarchical approach. A three-level name model that supports attributed names for objects in a distributed system and the structure of naming contexts which bind attributed names onto objects are presented. The naming contexts are represented intuitively with a context-graph. To be able to meet the requirements generated from the name service semantics, a name evaluation model suitable for different name services, i.e. the conventional service, the selection service and the enquiry service has been developed. This model allows the name evaluation to be implemented efficiently. Moreover, to achieve the effectiveness and the efficiency in the implementation of the name evaluation, we have developed a set of algorithms, each of which is for a particular name service.","PeriodicalId":404872,"journal":{"name":"Distributed Syst. Eng.","volume":"153 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131403450","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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