The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform

Sang H Son - One of the best experts on this subject based on the ideXlab platform.

  • multiversion Locking Protocol with freezing for secure real time database systems
    IEEE Transactions on Knowledge and Data Engineering, 2002
    Co-Authors: Chanjung Park, Seog Park, Sang H Son
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop Protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we propose a new multiversion concurrency control Protocol that ensures that both security and real-time requirements are met. The proposed Protocol is primarily based on Locking. However, in order to satisfy timing constraints and security requirements, a new method, called the freezing method, is proposed. In order to show that our Protocol provides a higher degree of concurrency than existing multiversion Protocols, we define a new serializability for multiversion concurrency control, called FR-serializability, which is more general than traditional serializability. We present several examples to illustrate the behavior of our Protocol, along with performance comparisons with other Protocols. The simulation results show significant performance improvement of the new Protocol.

  • priority driven secure multiversion Locking Protocol for real time secure database systems
    Proceedings of the IFIP TC11 WG11.3 Eleventh International Conference on Database Securty XI: Status and Prospects, 1997
    Co-Authors: Chanjung Park, Seog Park, Sang H Son
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically a timing constraint is expressed in the form of a deadline and is represented by a priority to be used by schedulers. In many real-time applications, security is another important requirement, since the system maintains sensitive information to be shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, Protocols that satisfy both requirements need to be developed.

  • design and analysis of an adaptive policy for secure real time Locking Protocol
    Information Sciences, 1997
    Co-Authors: Sang H Son, R David, Craig W Chaney
    Abstract:

    Abstract A secure concurrency control algorithm must, in addition to maintaining consistency of the database, be free from covert channels arising due to data conflicts between transactions. Since the property of noninterference must be satisfied to ensure security, most existing secure concurrency control algorithms are unfair to transactions at higher access classes. In this paper, a secure two-phase Locking Protocol is presented, which is shown to be free from covert channels. The Protocol provides reasonably fair execution of all transactions, regardless of their access class. Since many applications of advanced database systems need to support timeliness while managing sensitive information, integration of real-time transaction processing techniques with security Protocols is necessary. In this paper, we discuss the difficulties for supporting both security and timeliness, and present an adaptive scheme to support necessary tradeoffs to be made between security and timeliness requirements. An algorithm-independent simulation framework is explained, and the results of a performance evaluation of Secure 2PL is provided, comparing it with secure optimistic concurrency and secure multiversion timestamp ordering. The performance of the adaptive scheme is also evaluated for a spectrum of security-factor values ranging from fully secure (1.0) right up to fully real-time (0.0).

  • an adaptive policy for improved timeliness in secure database systems
    DBSec, 1995
    Co-Authors: Sang H Son, R David, Bhavani Thuraisingham
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions, in addition to maintaining data consistency. In addition to real-time requirements, security is usually required in many applications. Multilevel security requirements introduce a new dimension to transaction processing in real-time database systems. In this paper, we argue that because of the complexities involved, tradeoffs need to be made between security and timeliness. We first describe a secure two-phase Locking Protocol. The Protocol is then modified to support an adaptive method of trading off security for timeliness, depending on the current state of the system. The performance of the Adaptive 2PL Protocol is evaluated for a spectrum of security-factor values ranging from fully secure (1.0) right upto fully real-time (0.0).

  • design and analysis of a secure two phase Locking Protocol
    Computer Software and Applications Conference, 1994
    Co-Authors: Sang H Son, R David
    Abstract:

    In addition to maintaining consistency of the database, secure concurrency control algorithms must be free from covert channels arising due to data conflicts between transactions. The existing secure concurrency control approaches are unfair to transactions at higher access classes. A secure two-phase Locking Protocol is presented, which is correct and free from covert channels. The Protocol uses three different types of locks to support non-interference property and to provide reasonably fair execution of all transactions, regardless of their access class. The results of a performance evaluation of the Protocol are provided, comparing it with secure optimistic concurrency control and secure multiversion timestamp ordering. >

Seog Park - One of the best experts on this subject based on the ideXlab platform.

  • multiversion Locking Protocol with freezing for secure real time database systems
    IEEE Transactions on Knowledge and Data Engineering, 2002
    Co-Authors: Chanjung Park, Seog Park, Sang H Son
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop Protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we propose a new multiversion concurrency control Protocol that ensures that both security and real-time requirements are met. The proposed Protocol is primarily based on Locking. However, in order to satisfy timing constraints and security requirements, a new method, called the freezing method, is proposed. In order to show that our Protocol provides a higher degree of concurrency than existing multiversion Protocols, we define a new serializability for multiversion concurrency control, called FR-serializability, which is more general than traditional serializability. We present several examples to illustrate the behavior of our Protocol, along with performance comparisons with other Protocols. The simulation results show significant performance improvement of the new Protocol.

  • site Locking Protocol for global concurrency control in multidatabase systems
    International Database Engineering and Applications Symposium, 1999
    Co-Authors: Kyuwoong Lee, Myungjoon Kim, Seog Park
    Abstract:

    Much research into managing global transactions in multidatabase systems (MDBS) has been proposed to solve problems of ensuring global serializability. In these methods, a few opportunities are provided to the global transaction to execute concurrently. We concentrate our attention on 1) maintaining a consistent database state that is defined by global integrity constraints, and 2) investigation into the more accurate indirect conflict situation so that the global transaction manager (GTM) of MDBS provides a higher degree of concurrency. In this paper, we propose a site-Locking concurrency control method in MDBS. In our method more global transactions can be concurrently executed, since the refined boundary of possibility of indirect conflict is offered.

  • alternative correctness criteria for multiversion concurrency control and a Locking Protocol via freezing
    International Database Engineering and Applications Symposium, 1997
    Co-Authors: Chanjung Park, Seog Park
    Abstract:

    Concurrency control Protocols based on multiversions have been used in some commercial transaction processing systems in order to provide the serializable executions of transactions. In the existing Protocols, transactions are allowed to read only the most recent version of each data item in order to ensure the correct execution of transactions. However this feature is not desirable in some advanced database systems which have more requirements such as timing or security constraints besides serializability. We propose a new correctness criteria, called F-serializability, for multiversion concurrency control Protocols. It is the extended definition of 'l-serial' and relaxes the condition so that a Protocol provides not only the most recent version but also the previous one to transactions, if necessary. We prove that whenever a multiversion schedule is F-serializable, the schedule is also one-copy serializable. This is the first contribution of our paper. Next, we propose a new concurrency control Protocol for multilevel secure (MLS) database systems which guarantees the proposed serializability. In an MLS database system, a transaction scheduler must satisfy security constraints as well as ensure the serializable execution of transactions.

  • priority driven secure multiversion Locking Protocol for real time secure database systems
    Proceedings of the IFIP TC11 WG11.3 Eleventh International Conference on Database Securty XI: Status and Prospects, 1997
    Co-Authors: Chanjung Park, Seog Park, Sang H Son
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically a timing constraint is expressed in the form of a deadline and is represented by a priority to be used by schedulers. In many real-time applications, security is another important requirement, since the system maintains sensitive information to be shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, Protocols that satisfy both requirements need to be developed.

  • a multiversion Locking Protocol for real time databases with multilevel security
    Embedded and Real-Time Computing Systems and Applications, 1996
    Co-Authors: Chanjung Park, Seog Park
    Abstract:

    In this paper, we propose a new multiversion Locking Protocol for real-time database systems for providing multilevel security. Real-Time DBMS (RTDBMS) is a system that processes transactions with explicit timing constraints. Thus, it must satisfy not only logical data consistency but also timing constraints associated with transactions. There are increasing needs for security in many applications including real-time database systems. Multilevel security requirements introduce a new dimension to transaction processing in RTDBMS. In multilevel secure (MLS) database systems, a user's access is restricted based on the clearance of the user and the classification of data. There exist conflicting natures between timing constraints and security requirements. We propose a new Protocol ensuring both two conflicting requirements. We first classify transactions according to their priorities and security levels. Next, the compatibility matrix and a new version selection algorithm for our Protocol are presented. In addition, the conditions for satisfying relative temporal consistency are given.

Chanjung Park - One of the best experts on this subject based on the ideXlab platform.

  • multiversion Locking Protocol with freezing for secure real time database systems
    IEEE Transactions on Knowledge and Data Engineering, 2002
    Co-Authors: Chanjung Park, Seog Park, Sang H Son
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop Protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we propose a new multiversion concurrency control Protocol that ensures that both security and real-time requirements are met. The proposed Protocol is primarily based on Locking. However, in order to satisfy timing constraints and security requirements, a new method, called the freezing method, is proposed. In order to show that our Protocol provides a higher degree of concurrency than existing multiversion Protocols, we define a new serializability for multiversion concurrency control, called FR-serializability, which is more general than traditional serializability. We present several examples to illustrate the behavior of our Protocol, along with performance comparisons with other Protocols. The simulation results show significant performance improvement of the new Protocol.

  • alternative correctness criteria for multiversion concurrency control and a Locking Protocol via freezing
    International Database Engineering and Applications Symposium, 1997
    Co-Authors: Chanjung Park, Seog Park
    Abstract:

    Concurrency control Protocols based on multiversions have been used in some commercial transaction processing systems in order to provide the serializable executions of transactions. In the existing Protocols, transactions are allowed to read only the most recent version of each data item in order to ensure the correct execution of transactions. However this feature is not desirable in some advanced database systems which have more requirements such as timing or security constraints besides serializability. We propose a new correctness criteria, called F-serializability, for multiversion concurrency control Protocols. It is the extended definition of 'l-serial' and relaxes the condition so that a Protocol provides not only the most recent version but also the previous one to transactions, if necessary. We prove that whenever a multiversion schedule is F-serializable, the schedule is also one-copy serializable. This is the first contribution of our paper. Next, we propose a new concurrency control Protocol for multilevel secure (MLS) database systems which guarantees the proposed serializability. In an MLS database system, a transaction scheduler must satisfy security constraints as well as ensure the serializable execution of transactions.

  • priority driven secure multiversion Locking Protocol for real time secure database systems
    Proceedings of the IFIP TC11 WG11.3 Eleventh International Conference on Database Securty XI: Status and Prospects, 1997
    Co-Authors: Chanjung Park, Seog Park, Sang H Son
    Abstract:

    Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically a timing constraint is expressed in the form of a deadline and is represented by a priority to be used by schedulers. In many real-time applications, security is another important requirement, since the system maintains sensitive information to be shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, Protocols that satisfy both requirements need to be developed.

  • a multiversion Locking Protocol for real time databases with multilevel security
    Embedded and Real-Time Computing Systems and Applications, 1996
    Co-Authors: Chanjung Park, Seog Park
    Abstract:

    In this paper, we propose a new multiversion Locking Protocol for real-time database systems for providing multilevel security. Real-Time DBMS (RTDBMS) is a system that processes transactions with explicit timing constraints. Thus, it must satisfy not only logical data consistency but also timing constraints associated with transactions. There are increasing needs for security in many applications including real-time database systems. Multilevel security requirements introduce a new dimension to transaction processing in RTDBMS. In multilevel secure (MLS) database systems, a user's access is restricted based on the clearance of the user and the classification of data. There exist conflicting natures between timing constraints and security requirements. We propose a new Protocol ensuring both two conflicting requirements. We first classify transactions according to their priorities and security levels. Next, the compatibility matrix and a new version selection algorithm for our Protocol are presented. In addition, the conditions for satisfying relative temporal consistency are given.

Shihying Chen - One of the best experts on this subject based on the ideXlab platform.

  • a high concurrency xpath based Locking Protocol for xml databases
    Information & Software Technology, 2006
    Co-Authors: Kuenfang Jea, Shihying Chen
    Abstract:

    Abstract Providing efficient access to XML documents becomes crucial in XML database systems. More and more concurrency control Protocols for XML database systems were proposed in the past few years. Being an important language for addressing data in XML documents, XPath expressions are the basis of several query languages, such as XQurey and XSLT. In this paper, we propose a lock-based concurrency control Protocol, called XLP, for transactions accessing XML data by the XPath model. XLP is based on the XPath model and has the features of rich lock modes, low lock conflict and lock conversion. XLP is also proved to ensure conflict serializability. In sum, there are three major contributions in this paper. The proposed XLP supports most XPath axes, rather than simple path expressions only. Conflict conditions and rules in the XPath model are analyzed and derived. Moreover, a lightweighted lock mode, P-lock, is invented and integrated into XLP for better concurrency.

  • concurrency control in xml document databases xpath Locking Protocol
    International Conference on Parallel and Distributed Systems, 2002
    Co-Authors: Kuenfang Jea, Shihying Chen, Shenghsien Wang
    Abstract:

    XML has become the most important technique to exchange data in WWW. Providing efficient access to XML document databases is thus crucial. Concurrency control Protocols allow transactions to be executed concurrently to improve performance. However no proposed research aims at the concurrency control Protocol for XML databases. In this paper we propose a lock-based concurrency control Protocol, called XLP for XML documents. XLP takes into consideration the access behavior of the XPath model, which is an important language for addressing data in XML documents suggested by W3C XLP has the features of richer lock modes, refined lock granularity, lower lock conflict and lock conversion. We prove that XLP always generates serializable schedules. Our simulation results show that, for XML documents of different sizes, XLP outperforms 2PL by 84.4% on average and outperforms the tree Locking Protocol by 95.6% on average. The performance comparison of XLP with both 2PL and the tree Locking Protocol is also made in this study for various transactions with different XPath lengths, read/write ratios and the existence of predicates.

Bjorn B. Brandenburg - One of the best experts on this subject based on the ideXlab platform.

  • BLocking Optimality in Distributed Real-Time Locking Protocols
    2015
    Co-Authors: Bjorn B. Brandenburg
    Abstract:

    Lower and upper bounds on the maximum prior-ity inversion bLocking (pi-bLocking) that is gener-ally unavoidable in distributed multiprocessor real-time Locking Protocols (where resources may be accessed only from specific synchronization proces-sors) are established. Prior work on suspension-based shared-memory multiprocessor Locking proto-cols (which require resources to be accessible from all processors) has established asymptotically tight bounds of Ω(m) and Ω(n) maximum pi-bLocking under suspension-oblivious and suspension-aware analysis, respectively, where m denotes the total number of processors and n denotes the number of tasks. In this paper, it is shown that, in the case of distributed semaphore Protocols, there exist two different task allocation scenarios that give rise to distinct lower bounds. In the case of co-hosted task allocation, where application tasks may also be assigned to synchronization processors (i.e., pro-cessors hosting critical sections), Ω(Φ ·n) maximum pi-bLocking is unavoidable for some tasks under any Locking Protocol under both suspension-aware and suspension-oblivious schedulability analysis, where Φ denotes the ratio of the maximum response time to the shortest period. In contrast, in the case of disjoint task allocation (i.e., if application tasks may not be assigned to synchronization processors), only Ω(m) and Ω(n) maximum pi-bLocking is fun-damentally unavoidable under suspension-oblivious and suspension-aware analysis, respectively, as in the shared-memory case. These bounds are shown to be asymptotically tight with the construction of two new distributed real-time Locking Protocols that ensure O(m) and O(n) maximum pi-bLocking under suspension-oblivious and suspension-aware analysis, respectively

  • the fmlp an asymptotically optimal real time Locking Protocol for suspension aware analysis
    Euromicro Conference on Real-Time Systems, 2014
    Co-Authors: Bjorn B. Brandenburg
    Abstract:

    Multiprocessor real-time Locking Protocols that are asymptotically optimal under suspension-oblivious schedulability analysis (where suspensions are pessimistically modeled as processor demand) are known for partitioned, global, and clustered job-level fixed priority (JLFP) scheduling. However, for the case of more accurate suspension-aware schedulability analysis (where suspensions are accounted for explicitly), asymptotically optimal Protocols are known only for partitioned JLFP scheduling. In this paper, the gap is closed with the introduction of the first semaphore Protocol for suspension-aware analysis that is asymptotically optimal under global and clustered JLFP scheduling. To this end, a new progress mechanism that avoids repeated priority inversions is developed and analyzed, based on the key observation that if lock-holding, low-priority jobs are priority-boosted, then certain other non-lock-holding, higher-priority jobs must be co-boosted.

  • An asymptotically optimal real-time Locking Protocol for clustered scheduling under suspension-aware analysis
    ACM SIGBED Review, 2013
    Co-Authors: Bjorn B. Brandenburg
    Abstract:

    The purpose of real-time Locking Protocols is to limit priority inversions [5], which, intuitively, occur when a high-priority task is delayed by a lower-priority task. Such Locking-related delay, also called priority inversion bLocking (pi-bLocking), is problematic in real-time systems because it can result in deadline misses. However, some pi-bLocking is unavoidable when using locks and thus must be bounded and accounted for during schedulability analysis.

  • a flexible real time Locking Protocol for multiprocessors
    Embedded and Real-Time Computing Systems and Applications, 2007
    Co-Authors: A Block, Bjorn B. Brandenburg, H Leontyev, James H Anderson
    Abstract:

    Real-time scheduling algorithms for multiprocessor systems have been the subject of considerable recent interest. For such an algorithm to be truly useful in practice, support for semaphore-based Locking must be provided. However, for many global scheduling algorithms, no such mechanisms have been proposed. Furthermore, in the partitioned case, most prior semaphore schemes are either inefficient or restrict critical sections considerably. In this paper, a new flexible multiprocessor Locking scheme is presented that can be applied under both partitioning and global scheduling. This scheme allows unrestricted critical-section nesting, but has been designed to deal with the common case of short non-nested accesses efficiently.