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1.
Concurrency control in hierarchical multidatabase systems 总被引:1,自引:0,他引:1
Sharad Mehrotra Henry F. Korth Avi Silberschatz 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(2):152-172
Over the past decade, significant research has been done towards developing transaction management algorithms for multidatabase
systems. Most of this work assumes a monolithic architecture of the multidatabase system with a single software module that
follows a single transaction management algorithm to ensure the consistency of data stored in the local databases. This monolithic
architecture is not appropriate in a multidatabase environment where the system spans multiple different organizations that
are distributed over various geographically distant locations. In this paper, we propose an alternative multidatabase transaction
management architecture, where the system is hierarchical in nature. Hierarchical architecture has consequences on the design
of transaction management algorithms. An implication of the architecture is that the transaction management algorithms followed
by a multidatabase system must be composable– that is, it must be possible to incorporate individual multidatabase systems as elements in a larger multidatabase system.
We present a hierarchical architecture for a multidatabase environment and develop techniques for concurrency control in such
systems.
Edited by R. Sacks-Davis. Received June 27, 1994 / Accepted September 26, 1995 相似文献
2.
Data placement in shared-nothing parallel database systems 总被引:4,自引:0,他引:4
Manish Mehta David J. DeWitt 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(1):53-72
Data placement in shared-nothing database systems has been studied extensively in the past and various placement algorithms
have been proposed. However, there is no consensus on the most efficient data placement algorithm and placement is still performed
manually by a database administrator with periodic reorganization to correct mistakes. This paper presents the first comprehensive
simulation study of data placement issues in a shared-nothing system. The results show that current hardware technology trends
have significantly changed the performance tradeoffs considered in past studies. A simplistic data placement strategy based
on the new results is developed and shown to perform well for a variety of workloads.
Edited by M. Adiba. Received May 11, 1993 / Accepted April 24, 1996 November 1, 1995 相似文献
3.
Secure buffering in firm real-time database systems 总被引:2,自引:0,他引:2
Binto George Jayant R. Haritsa 《The VLDB Journal The International Journal on Very Large Data Bases》2000,8(3-4):178-198
Many real-time database applications arise in electronic financial services, safety-critical installations and military systems
where enforcing security is crucial to the success of the enterprise. We investigate here the performance implications, in terms of killed transactions,
of guaranteeing multi-level secrecy in a real-time database system supporting applications with firm deadlines. In particular, we focus on the buffer management aspects of this issue.
Our main contributions are the following. First, we identify the importance and difficulties of providing secure buffer management
in the real-time database environment. Second, we present SABRE, a novel buffer management algorithm that provides covert-channel-free security. SABRE employs a fully dynamic one-copy allocation policy for efficient usage of buffer resources. It also incorporates
several optimizations for reducing the overall number of killed transactions and for decreasing the unfairness in the distribution
of killed transactions across security levels. Third, using a detailed simulation model, the real-time performance of SABRE
is evaluated against unsecure conventional and real-time buffer management policies for a variety of security-classified transaction
workloads and system configurations. Our experiments show that SABRE provides security with only a modest drop in real-time
performance. Finally, we evaluate SABRE's performance when augmented with the GUARD adaptive admission control policy. Our
experiments show that this combination provides close to ideal fairness for real-time applications that can tolerate covert-channel
bandwidths of up to one bit per second (a limit specified in military standards).
Received March 1, 1999 / Accepted October 1, 1999 相似文献
4.
Building knowledge base management systems 总被引:1,自引:0,他引:1
John Mylopoulos Vinay Chaudhri Dimitris Plexousakis Adel Shrufi Thodoros Topologlou 《The VLDB Journal The International Journal on Very Large Data Bases》1996,5(4):238-263
Advanced applications in fields such as CAD, software engineering, real-time process control, corporate repositories and digital
libraries require the construction, efficient access and management of large, shared knowledge bases. Such knowledge bases
cannot be built using existing tools such as expert system shells, because these do not scale up, nor can they be built in
terms of existing database technology, because such technology does not support the rich representational structure and inference
mechanisms required for knowledge-based systems. This paper proposes a generic architecture for a knowledge base management
system intended for such applications. The architecture assumes an object-oriented knowledge representation language with
an assertional sublanguage used to express constraints and rules. It also provides for general-purpose deductive inference
and special-purpose temporal reasoning. Results reported in the paper address several knowledge base management issues. For
storage management, a new method is proposed for generating a logical schema for a given knowledge base. Query processing
algorithms are offered for semantic and physical query optimization, along with an enhanced cost model for query cost estimation.
On concurrency control, the paper describes a novel concurrency control policy which takes advantage of knowledge base structure
and is shown to outperform two-phase locking for highly structured knowledge bases and update-intensive transactions. Finally,
algorithms for compilation and efficient processing of constraints and rules during knowledge base operations are described.
The paper describes original results, including novel data structures and algorithms, as well as preliminary performance evaluation
data. Based on these results, we conclude that knowledge base management systems which can accommodate large knowledge bases
are feasible.
Edited by Gunter Schlageter and H.-J. Schek.
Received May 19, 1994 / Revised May 26, 1995 / Accepted September 18, 1995 相似文献
5.
Scene change detection techniques for video database systems 总被引:1,自引:0,他引:1
Haitao Jiang Abdelsalam Helal Ahmed K. Elmagarmid Anupam Joshi 《Multimedia Systems》1998,6(3):186-195
Scene change detection (SCD) is one of several fundamental problems in the design of a video database management system (VDBMS).
It is the first step towards the automatic segmentation, annotation, and indexing of video data. SCD is also used in other
aspects of VDBMS, e.g., hierarchical representation and efficient browsing of the video data. In this paper, we provide a
taxonomy that classifies existing SCD algorithms into three categories: full-video-image-based, compressed-video-based, and
model-based algorithms. The capabilities and limitations of the SCD algorithms are discussed in detail. The paper also proposes
a set of criteria for measuring and comparing the performance of various SCD algorithms. We conclude by discussing some important
research directions. 相似文献
6.
Managing database server performance to meet QoS requirements in electronic commerce systems 总被引:1,自引:0,他引:1
Patrick Martin Wendy Powley Hoi-Ying Li Keri Romanufa 《International Journal on Digital Libraries》2002,3(4):316-324
The performance of electronic commerce systems has a major impact on their acceptability to users. Different users also demand
different levels of performance from the system, that is, they will have different Quality of Service (QoS) requirements. Electronic commerce systems are the integration of several different types of servers and each server must
contribute to meeting the QoS demands of the users. In this paper we focus on the role, and the performance, of a database server within an electronic commerce system.
We examine the characteristics of the workload placed on a database server by an electronic commerce system and suggest a
range of QoS requirements for the database server based on this analysis of the workload. We argue that a database server
must be able to dynamically reallocate its resources in order to meet the QoS requirements of different transactions as the
workload changes. We describe Quartermaster, which is a system to support dynamic goal-oriented resource management in database
management systems, and discuss how it can be used to help meet the QoS requirements of the electronic commerce database server.
We provide an example of the use of Quartermaster that illustrates how the dynamic reallocation of memory resources can be
used to meet the QoS requirements of a set of transactions similar to transactions found in an electronic commerce workload.
We briefly describe the memory reallocation algorithms used by Quartermaster and present experiments to show the impact of
the reallocations on the performance of the transactions.
Published online: 22 August 2001 相似文献
7.
Concurrency control schemes for object-oriented database systems (OODBSs) used in the area of performance-critical applications should increase the degree of concurrency and decrease locking overhead in order to offer maximum performance. However, most commercially available OODBSs use conventional concurrency control schemes that never exploit the rich semantics of object-oriented data model, thus fail to offer better performance. In this paper, we propose a concurrency control scheme for OODBSs, called in-place semantic multigranularity locking (ISMGL), that not only exploits semantics regarding methods to enhance the concurrency degree, but also utilizes multigranularity locking rules to decrease locking overhead. The novel aspect of ISMGL is that it combines conventional multigranularity locking and nested transaction model with utilizing commutativity of methods. Our concurrency control scheme is applicable for realistic OODBSs in the presence of complex objects with shared subobjects. Lastly, we evaluate the performance of ISMGL by using a simulation study. 相似文献
8.
Semantic integrity support in SQL:1999 and commercial (object-)relational database management systems 总被引:1,自引:0,他引:1
Can Türker Michael Gertz 《The VLDB Journal The International Journal on Very Large Data Bases》2001,10(4):241-269
The correctness of the data managed by database systems is vital to any application that utilizes data for business, research,
and decision-making purposes. To guard databases against erroneous data not reflecting real-world data or business rules,
semantic integrity constraints can be specified during database design. Current commercial database management systems provide
various means to implement mechanisms to enforce semantic integrity constraints at database run-time.
In this paper, we give an overview of the semantic integrity support in the most recent SQL-standard SQL:1999, and we show
to what extent the different concepts and language constructs proposed in this standard can be found in major commercial (object-)relational
database management systems. In addition, we discuss general design guidelines that point out how the semantic integrity features
provided by these systems should be utilized in order to implement an effective integrity enforcing subsystem for a database.
Received: 14 August 2000 / Accepted: 9 March 2001 / Published online: 7 June 2001 相似文献
9.
Deadlock detection in distributed database systems: a new algorithm and a comparative performance analysis 总被引:4,自引:0,他引:4
Natalija Krivokapić Alfons Kemper Ehud Gudes 《The VLDB Journal The International Journal on Very Large Data Bases》1999,8(2):79-100
This paper attempts a comprehensive study of deadlock detection in distributed database systems. First, the two predominant
deadlock models in these systems and the four different distributed deadlock detection approaches are discussed. Afterwards,
a new deadlock detection algorithm is presented. The algorithm is based on dynamically creating deadlock detection agents (DDAs), each being responsible for detecting deadlocks in one connected component of the global wait-for-graph (WFG). The
DDA scheme is a “self-tuning” system: after an initial warm-up phase, dedicated DDAs will be formed for “centers of locality”,
i.e., parts of the system where many conflicts occur. A dynamic shift in locality of the distributed system will be responded
to by automatically creating new DDAs while the obsolete ones terminate. In this paper, we also compare the most competitive
representative of each class of algorithms suitable for distributed database systems based on a simulation model, and point
out their relative strengths and weaknesses. The extensive experiments we carried out indicate that our newly proposed deadlock
detection algorithm outperforms the other algorithms in the vast majority of configurations and workloads and, in contrast
to all other algorithms, is very robust with respect to differing load and access profiles.
Received December 4, 1997 / Accepted February 2, 1999 相似文献
10.
11.
Wen-Syan Li K.Selçuk Candan Kyoji Hirata Yoshinori Hara 《The VLDB Journal The International Journal on Very Large Data Bases》2001,9(4):312-326
Due to the fuzziness of query specification and media matching, multimedia retrieval is conducted by way of exploration.
It is essential to provide feedback so that users can visualize query reformulation alternatives and database content distribution.
Since media matching is an expensive task, another issue is how to efficiently support exploration so that the system is not
overloaded by perpetual query reformulation. In this paper, we present a uniform framework to represent statistical information
of both semantics and visual metadata for images in the databases. We propose the concept of query verification, which evaluates queries using statistics, and provides users with feedback, including the strictness and reformulation alternatives
of each query condition as well as estimated numbers of matches. With query verification, the system increases the efficiency
of the multimedia database exploration for both users and the system. Such statistical information is also utilized to support
progressive query processing and query relaxation.
Received: 9 June 1998/ Accepted: 21 July 2000 Published online: 4 May 2001 相似文献
12.
Analysis of navigation behaviour in web sites integrating multiple information systems 总被引:6,自引:0,他引:6
Bettina Berendt Myra Spiliopoulou 《The VLDB Journal The International Journal on Very Large Data Bases》2000,9(1):56-75
Abstract. The analysis of web usage has mostly focused on sites composed of conventional static pages. However, huge amounts of information
available in the web come from databases or other data collections and are presented to the users in the form of dynamically
generated pages. The query interfaces of such sites allow the specification of many search criteria. Their generated results
support navigation to pages of results combining cross-linked data from many sources. For the analysis of visitor navigation
behaviour in such web sites, we propose the web usage miner (WUM), which discovers navigation patterns subject to advanced
statistical and structural constraints. Since our objective is the discovery of interesting navigation patterns, we do not
focus on accesses to individual pages. Instead, we construct conceptual hierarchies that reflect the query capabilities used
in the production of those pages. Our experiments with a real web site that integrates data from multiple databases, the German
SchulWeb, demonstrate the appropriateness of WUM in discovering navigation patterns and show how those discoveries can help
in assessing and improving the quality of the site.
Received June 21, 1999 / Accepted December 24, 1999 相似文献
13.
Paul Clark Majid Mirmehdi 《International Journal on Document Analysis and Recognition》2002,4(4):243-257
We present two different approaches to the location and recovery of text in images of real scenes. The techniques we describe
are invariant to the scale and 3D orientation of the text, and allow recovery of text in cluttered scenes. The first approach
uses page edges and other rectangular boundaries around text to locate a surface containing text, and to recover a fronto-parallel
view. This is performed using line detection, perceptual grouping, and comparison of potential text regions using a confidence
measure. The second approach uses low-level texture measures with a neural network classifier to locate regions of text in
an image. Then we recover a fronto-parallel view of each located paragraph of text by separating the individual lines of text
and determining the vanishing points of the text plane. We illustrate our results using a number of images.
Received May 20, 2001 / Accepted June 19, 2001 相似文献
14.
Sérgio Vale Aguiar Campos Edmund Clarke 《International Journal on Software Tools for Technology Transfer (STTT)》1999,2(3):260-269
The task of checking if a computer system satisfies its timing specifications is extremely important. These systems are often
used in critical applications where failure to meet a deadline can have serious or even fatal consequences. This paper presents
an efficient method for performing this verification task. In the proposed method a real-time system is modeled by a state-transition
graph represented by binary decision diagrams. Efficient symbolic algorithms exhaustively explore the state space to determine
whether the system satisfies a given specification. In addition, our approach computes quantitative timing information such
as minimum and maximum time delays between given events. These results provide insight into the behavior of the system and
assist in the determination of its temporal correctness. The technique evaluates how well the system works or how seriously
it fails, as opposed to only whether it works or not. Based on these techniques a verification tool called Verus has been constructed. It has been used in the verification of several industrial real-time systems such as the robotics system
described below. This demonstrates that the method proposed is efficient enough to be used in real-world designs. The examples
verified show how the information produced can assist in designing more efficient and reliable real-time systems. 相似文献
15.
Georgios Evangelidis David Lomet Betty Salzberg 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(1):1-25
We propose a new multi-attribute index. Our approach combines the hB-tree, a multi-attribute index, and the -tree, an abstract index which offers efficient concurrency and recovery methods. We call the resulting method the hB-tree. We describe several versions of the hB-tree, each using a different node-splitting and index-term-posting algorithm. We also describe a new node deletion algorithm.
We have implemented all the versions of the hB-tree. Our performance results show that even the version that offers no performance guarantees, actually performs very well
in terms of storage utilization, index size (fan-out), exact-match and range searching, under various data types and distributions.
We have also shown that our index is fairly insensitive to increases in dimension. Thus, it is suitable for indexing high-dimensional
applications. This property and the fact that all our versions of the hB-tree can use the -tree concurrency and recovery algorithms make the hB-tree a promising candidate for inclusion in a general-purpose DBMS.
Edited by R. Sacks-Davis. Received 27 June 1994 / Accepted 26 September 1995 相似文献
16.
PicoDBMS: Scaling down database techniques for the smartcard 总被引:1,自引:0,他引:1
Philippe Pucheral Luc Bouganim Patrick Valduriez Christophe Bobineau 《The VLDB Journal The International Journal on Very Large Data Bases》2001,10(2-3):120-132
Smartcards are the most secure portable computing device today. They have been used successfully in applications involving
money, and proprietary and personal data (such as banking, healthcare, insurance, etc.). As smartcards get more powerful (with
32-bit CPU and more than 1 MB of stable memory in the next versions) and become multi-application, the need for database management
arises. However, smartcards have severe hardware limitations (very slow write, very little RAM, constrained stable memory,
no autonomy, etc.) which make traditional database technology irrelevant. The major problem is scaling down database techniques
so they perform well under these limitations. In this paper, we give an in-depth analysis of this problem and propose a PicoDBMS
solution based on highly compact data structures, query execution without RAM, and specific techniques for atomicity and durability.
We show the effectiveness of our techniques through performance evaluation.
Received: 15 October 2000 / Accepted: 15 April 2001 Published online: 23 July 2001 相似文献
17.
E. Panagos A. Biliris 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(3):209-223
Client-server object-oriented database management systems differ significantly from traditional centralized systems in terms
of their architecture and the applications they target. In this paper, we present the client-server architecture of the EOS
storage manager and we describe the concurrency control and recovery mechanisms it employs. EOS offers a semi-optimistic locking
scheme based on the multi-granularity two-version two-phase locking protocol. Under this scheme, multiple concurrent readers
are allowed to access a data item while it is being updated by a single writer. Recovery is based on write-ahead redo-only
logging. Log records are generated at the clients and they are shipped to the server during normal execution and at transaction
commit. Transaction rollback is fast because there are no updates that have to be undone, and recovery from system crashes
requires only one scan of the log for installing the changes made by transactions that committed before the crash. We also
present a preliminary performance evaluation of the implementation of the above mechanisms.
Edited by R. King. Received July 1993 / Accepted May 1996 相似文献
18.
Zengping Tian Hongjun Lu Wenyun Ji Aoying Zhou Zhong Tian 《International Journal on Digital Libraries》2002,3(4):325-331
Detecting and eliminating duplicate records is one of the major tasks for improving data quality. The task, however, is not
as trivial as it seems since various errors, such as character insertion, deletion, transposition, substitution, and word
switching, are often present in real-world databases. This paper presents an n-gram-based approach for detecting duplicate
records in large databases. Using the approach, records are first mapped to numbers based on the n-grams of their field values.
The obtained numbers are then clustered, and records within a cluster are taken as potential duplicate records. Finally, record
comparisons are performed within clusters to identify true duplicate records. The unique feature of this method is that it
does not require preprocessing to correct syntactic or typographical errors in the source data in order to achieve high accuracy.
Moreover, sorting the source data file is unnecessary. Only a fixed number of database scans is required. Therefore, compared
with previous methods, the algorithm is more time efficient.
Published online: 22 August 2001 相似文献
19.
David Lomet Betty Salzberg 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(3):224-240
Although many suggestions have been made for concurrency in B-trees, few of these have considered recovery as well. We describe an approach which provides high concurrency while preserving
well-formed trees across system crashes. Our approach works for a class of index trees that is a generalization of the B-tree. This class includes some multi-attribute indexes and temporal indexes. Structural changes in an index tree are decomposed
into a sequence of atomic actions, each one leaving the tree well-formed and each working on a separate level of the tree.
All atomic actions on levels of the tree above the leaf level are independent of database transactions, and so are of short
duration. Incomplete structural changes are detected in normal operations and trigger completion.
Edited by A. Reuter. Received August 1995 / accepted July 1996 相似文献
20.
Algebraic query optimisation for database programming languages 总被引:1,自引:0,他引:1
Alexandra Poulovassilis Carol Small 《The VLDB Journal The International Journal on Very Large Data Bases》1996,5(2):119-132
A major challenge still facing the designers and implementors of database
programming languages (DBPLs) is that of query optimisation. We investigate
algebraic query optimisation techniques for DBPLs in the context of a purely
declarative functional language that supports sets as first-class objects.
Since the language is computationally complete issues such as
non-termination of expressions and construction of infinite data structures
can be investigated, whilst its declarative nature allows the issue of side
effects to be avoided and a richer set of equivalences to be developed.
The language has a well-defined semantics which permits us to reason
formally about the properties of expressions, such as their equivalence with
other expressions and their termination. The support of a set bulk data
type enables much prior work on the optimisation of relational languages to
be utilised.
In the paper we first give the syntax of our archetypal DBPL and briefly
discuss its semantics. We then define a small but powerful algebra of
operators over the set data type, provide some key equivalences for
expressions in these operators, and list transformation principles for
optimising expressions. Along the way, we identify some caveats to
well-known equivalences for non-deductive database languages. We next
extend our language with two higher level constructs commonly found in
functional DBPLs: set comprehensions and functions with known inverses. Some
key equivalences for these constructs are provided, as are transformation
principles for expressions in them. Finally, we investigate extending our
equivalences for the set operators to the analogous operators over bags.
Although developed and formally proved in the context of a functional
language, our findings are directly applicable to other DBPLs of similar
expressiveness.
Edited by
Matthias Jarke, Jorge Bocca, Carlo Zaniolo. Received
September 15, 1994 / Accepted September 1, 1995 相似文献