Estimating nested selectivity in object-oriented and object-relational databases

A search condition in object-oriented/object-relational queries consists of nested predicates, which are predicates on path expressions. In this paper, we propose a new technique for estimating selectivity for nested predicates. Selectivity of a nested predicate, nested selectivity, is defined as the ratio of the number of the qualified objects of the starting class in the path expression to the total number of objects of the class. The new technique takes into account the effects of direct representation of the many-to-many relationship and the partial participation of objects in the relationship. These two features occur frequently in object-oriented/object-relational databases, but have not been properly handled in the conventional selectivity estimation techniques. For the many-to-many relationship, we generalize the block-hit function proposed by S.B. Yao to allow the cases that an object belongs to more than one block. For the partial participation, we propose the concept of active objects and extend our technique for total participation to handle active objects. We also propose efficient methods for obtaining statistical information needed for our estimation technique. We finally analyze the accuracy of our technique through a series of experiments and compare with the conventional ones. The experiment results showed that there was a significant inaccuracy in the estimation by the conventional ones, confirming the advantage of our technique.     

Index organizations for object-oriented database systems

We present an indexing technique providing support for queries involving complex, nested objects and inheritance hierarchies. This technique is compared with two techniques obtained from more traditional organizations. The three techniques are evaluated using an analytical cost model. The discussion is cast in the framework of object-oriented databases. However, results are applicable to data management systems characterized by features such as complex objects and inheritance hierarchies     

An evaluation of buffer management strategies for relational database systems

In this paper we present a new algorithm, DBMIN, for managing the buffer pool of a relational database management system. DBMIN is based on a new model of relational query behavior, thequery locality set model (QLSM). Like the hot set model, the QLSM has an advantage over the stochastic models due to its ability to predict future reference behavior. However, the QLSM avoids the potential problems of the hot set model by separating the modeling of reference behavior from any particular buffer management algorithm. After introducing the QLSM and describing the DBMIN algorithm, we present a performance evaluation methodology for evaluating buffer management algorithms in a multiuser environment. This methodology employed a hybrid model that combines features of both trace-driven and distribution-driven simulation models. Using this model, the performance of the DBMIN algorithm in a multiuser environment is compared with that of the hot set algorithm and four more traditional buffer replacement algorithms.This research was partially supported by the Department of Energy under Contract No. DE-AC02-81ER10920 and the National Science Foundation under grant MCS82-01870.     

An evaluation of buffer management strategies for relational database systems

In this paper we present a new algorithm, DBMIN, for managing the buffer pool of a relational database management system. DBMIN is based on a new model of relational query behavior, thequery locality set model (QLSM). Like the hot set model, the QLSM has an advantage over the stochastic models due to its ability to predict future reference behavior. However, the QLSM avoids the potential problems of the hot set model by separating the modeling of reference behavior from any particular buffer management algorithm. After introducing the QLSM and describing the DBMIN algorithm, we present a performance evaluation methodology for evaluating buffer management algorithms in a multiuser environment. This methodology employed a hybrid model that combines features of both trace-driven and distribution-driven simulation models. Using this model, the performance of the DBMIN algorithm in a multiuser environment is compared with that of the hot set algorithm and four more traditional buffer replacement algorithms.     

Issues in query model design in object-oriented database systems

The provision of a powerful query system, including a declarative query language and the systems support for efficiently processing queries is essential for the success of object-oriented database technology. Designing a query system involves making a large number of decisions, further complicated by the lack of a universally accepted object-oriented object data model. In this paper, object data model and query model design decisions are enumerated, alternatives are identified, and the tradeoffs are specified.     

Architecture of an open object-oriented database management system

The architecture of the open object-oriented database (OODB) management system, its requirements, and its computational model, which builds database functionality as an extensible collection of transparent extensions to existing programming languages, are described. The way in which open OODB's system architecture is decomposed into a kernal meta-architecture and a collection of modules implementing specific behavioral extensions is discussed. The potential risks of the open OODB architecture are reviewed     

Semantic multigranularity locking and its performance in object-oriented database systems

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.     

Integration of object-oriented programming languages and database systems in KOPERNIK

KOPERNIK is an object-oriented database system, that allows uniform specification of database requests and application programs. The user interface is based on Smalltalk, and the object-oriented data model is represented in terms of classes and messages. Techniques are discussed for implementing such a model on top of an underlying relational database system. Those parts of application programs that cannot be translated into a relational language are handled by a Smalltalk processor. The semantics of the database requests is defined in terms of a meta-model and meta-messages, using an object-oriented approach. Hence we derive rules for translation of database requests into SQL queries over a binary relational view, introduced as an intermediate level between the underlying database and our conceptual view.     

Integrating relational and object-oriented database systems using a metaclass concept

This paper presents a specific approach of integrating a relational database system into a federated database system. The underlying database integration process consist of three steps: first, the external database systems have to be connected to the integrated database system environment and the external data models have to be mapped into a canonical data model. This step is often called syntactic transformation including structural enrichment and leads to component schemas for each external DBMS. Second, the resulting schemas from the first step are used to construct export schemas which are then integrated into global, individual schemas or views in the third step. In this paper we focus on the first step for relational databases, i.e., the connection of a relational database system and the mapping of the relational model into a canonical data model. We take POSTGRES as the relational database system and the object-oriented federated database system VODAK as the integration platform which provides the open, object-oriented data model as the canonical data model for the integration. We show different variations of mapping the relational model. By exploiting the metaclass concept provided by VML, the modelling language of VODAK, we show how to tailor VML such that the canonical data model meets the requirements of integrating POSTGRES into the global database system VODAK in an efficient way.     

Life-cycle of a dual object-oriented specification model for real-time systems

Dual approaches for real-time systems specification try to integrate in a unique model/language the most interesting features of both operational and denotational approaches. In some cases, the object-oriented paradigm has been used for integrating the above aspects and as a support for covering with a uniform approach the development life-cycle from requirements analysis to application coding, by presenting initially a mainly denotational semantics which changes in operational semantics with the increase of implementation details. For these reasons, traditional development life-cycles are unsuitable, and more specific phases are needed to exploit the potentiality of the approach. In this paper, the authors present the life-cycle defined for a dual approach proposed in the literature—i.e., TOOMS/TROL.     

Formalization of object-oriented database model with rules

The paper investigates knowledge representation in an object-oriented database management system first within the data model with rules and second in the computational model by using logic. Issues of structure, integrity, and retrieval are focused on. The proposed system provides object-oriented concepts for describing complex structured data, rules for expressing object-dependent constraints and object associations, and, finally, logic for inference and retrieval.     

嵌入式实时数据库的安全缓冲区管理器的设计

分析嵌入式实时数据库安全缓冲管理算法SABRE,将其引入到开源数据库Berkeley DB的缓冲中,设计实时安全缓冲区管理器.一般实时数据库的缓冲区管理都基于优先级,在设计中将安全级别与优先级结合,构成综合优先级,可以根据系统的安全要求和实时特征动态调整权值以适应不同的要求,既满足实时也满足安全.主要有两种数据结构:安全级别队列数组和优先级队列数组.     

Applications of object-oriented technology to the integration of heterogeneous database systems

The object-oriented paradigm has several features that facilitate the integration of heterogeneous data management systems. One of the main problems in the integration is to provide users with the same data model and language to access very different systems. This problem exists in all kinds of distributed heterogeneous data management systems, independently from their integration architecture (like classical distributed databases, federated databases, multidatabases). This paper shows that the use of an object-oriented data model for building a uniform view of several databases can greatly simplify this task, and actually extends the scope of integration towards two directions. The first concerns the integration of data management systems to which traditional integration techniques, based on mappings among data models, cannot be applied. The second direction moves the goal of integration to re-using not only data but to re-using data and application software using these data. In the paper we also briefly discuss some requirements for an object-oriented integrated platform. Recommended by: F. Manola     

Multi-level security in database management systems

Multi-level secure database management system (MLS-DBMS) security requirements are defined in terms of the view of the database presented to users with different authorizations. These security requirements are intended to be consistent with DoD secure computing system requirements. An informal security policy for a multi-level secure database management system is outlined, and mechanisms are introduced that support the policy. Security constraints are the mechanism for defining classification rules, and query modification is the mechanism for implementing the classification policy. These mechanisms ensure that responses to users' queries can be assigned classifications which will make them observable to the querying users.     

Transaction management in distributed heterogeneous database management systems

Current distributed, heterogeneous database management systems (DBMSs) address the issue of distributed transaction management (DTM) in two different ways: some systems rely solely on unmodified local transaction managers (LTMs), thereby helping preserve local DBMS autonomy, but limit functionality (e.g. allow only unsynchronized retrievals, preclude distributed updates, etc.); others maintain full functionality but require the (re)design of the LTMs to enforce homogeneous DTM across all heterogeneous DBMSs, thereby giving up most of the local DBMS autonomy.

The goal of the work presented here is to establish the minimum set of modifications to LTMs that allow synchronized retrievals and distributed updates (whenever semantic conflicts can be resolved), and will continue to maintain a high degree of local DBMS autonomy. The problems of: (1) distribution of responsibility between DTM and LTMs, (2) concatenation of functionally-equivalent LTM mechanisms, and (3) providing compensation mechanisms for functionally-limited LTMs are introduced. Solutions to the above problems are shown to exist. However, the interconnection of autonomous, heterogeneous DBMSs is significantly more difficult than anticipated, despite communication standardization and current optimism.     

An object-oriented database management system for computer-aided design of tall buildings

An effective database and database management system is the key to the success of an integrated approach to software engineering applications in general, and Computer-Aided Design (CAD) for structural applications in particular. Due to the inherent nature of CAD data such as dynamic modeling, a wide range of data types, large data volume, etc., the traditional database models, such as hierarchical, network and relational models, are unable to handle the aforementioned applications satisfactorily. An object-oriented data modeling is known to be the most effective approach. However, many of the commercial object-oriented databases are designed for information management, and they are inadequate for CAD application due to the different features of the object-hierarchy and varying data management objectives during the design cycles. This paper presents a hierarchical index-based object-oriented database management model for CAD applications. To deal with the object hierarchy encountered in CAD for the design of tall buildings, the proposed database consists of several salient features: a hierarchical object model, its related storage structure, a data dictionary, a class factory and an index system. The proposed database management model has been implemented into an integrated CAD system for design application of tall buildings.     

Export database derivation in object-oriented wrappers

Wrappers export the schema and data of existing heterogeneous databases and support queries on them. In the context of cooperative information systems, we present a flexible approach to specify the derivation of object-oriented (OO) export databases from local relational databases. Our export database derivation consists of a set of extent derivation structures (EDS) which defines the extent and deep extent of export classes. Having well-defined semantics, the EDS can be readily used in transforming wrapper queries to local queries. Based on the EDS, we developed a wrapper query evaluation strategy which handles OO queries on the export databases. The strategy is unique in that it considers the limited query processing capabilities of local database systems as well as the language constraints on the local query languages.     

Dynamic neural-based buffer management for queuing systems with self-similar characteristics

Buffer management in queuing systems plays an important role in addressing the tradeoff between efficiency measured in terms of overall packet loss and fairness measured in terms of individual source packet loss. Complete partitioning (CP) of a buffer with the best fairness characteristic and complete sharing (CS) of a buffer with the best efficiency characteristic are at the opposite ends of the spectrum of buffer management techniques. Dynamic partitioning buffer management techniques aim at addressing the tradeoff between efficiency and fairness. Ease of implementation is the key issue when determining the practicality of a dynamic buffer management technique. In this paper, two novel dynamic buffer management techniques for queuing systems accommodating self-similar traffic patterns are introduced. The techniques take advantage of the adaptive learning power of perceptron neural networks when applied to arriving traffic patterns of queuing systems. Relying on the water-filling approach, our proposed techniques are capable of coping with the tradeoff between packet loss and fairness issues. Computer simulations reveal that both of the proposed techniques enjoy great efficiency and fairness characteristics as well as ease of implementation.     

Buffer management in real-time active database systems

Real-time active database systems (RTADB) have attracted the attention of researchers in recent times. Such systems are envisioned as control systems for environments as diverse as process control, network management and automated financial trading. Sensors distributed throughout the system report the state of the system to the database. Unacceptable state reports typically results in corrective actions being triggered with deadlines. Thus RTADB's incorporate both real-time as well as active characteristics. We study buffer management in RTADB. Buffer management is recognized as not being a well studied area in real-time systems. As a result of our work, we postulate PAPER, a new buffer management scheme that relies on two strategies: prefetching and priority based buffer replacement. We report the result of studies of the performance of PAPER, as compared to that of existing buffer management algorithms. The insights derived from this paper impact both real-time database systems as well as real-time, active database systems     

Global lock escalation in database management systems

Since database management systems (DBMSs) have limited lock resources, transactions requesting locks beyond the limit must be aborted, degrading the performance abruptly. Lock escalation can be effectively used in such circumstances to alleviate the problem. Many lock escalation methods have been proposed and implemented in commercial DBMSs. However, they have certain problems due to the local nature of their decisions on when to execute lock escalation. In this paper, we propose a new lock escalation method, global lock escalation, that makes such decision globally based on the total number of locks. Through extensive simulation, we show that the global lock escalation method outperforms the existing ones significantly. Especially, we show that the number of concurrent transactions allowable increases by 2-16 times. We believe our method can be easily implemented in the commercial DBMSs enhancing the performance significantly under excessive lock requests.