Property of separability in physical design of network model databases

We present a physical design methodology for network model databases based on the theory of separability. In particular, we present a cost model and a usage specification scheme that are suitable for describing the network model database environment. We subsequently prove that, under these usage and cost models, a large subset of practically important access structures that are available in network model database systems satisfies the conditions for separability. The theory of separability was introduced in an earlier work, in the context of relational systems, as a formal basis for partitioning the problem of designing the optimal physical database. The theory proves that, given a certain set of access structures and a usage specification scheme, the problem of optimal assignment of access structures to the entire database can be reduced to the subproblem of optimizing individual record types independently of one another. The approach we present significantly reduces the complexity of the design problem which has the potential of being combinatorially explosive. A heuristic extension of the formal methodology to the access structures not incorporated in the theory is also discussed.     

Computing access relevance for path-method generation in OODB and IM-OODB

A path-method (PM) is a mechanism to retrieve or to update information relevant to one class, in an object-oriented database (OODB), that is not stored with that class but with some other class. The PM traverses a chain of classes and connections that ends at the class where the required information is stored. However, it is a difficult task for a user to write PMs. This is because it might require comprehensive knowledge of many classes of the conceptual schema. But a typical user has often incomplete or even inconsistent knowledge of the schema. Currently we are developing a system, called Path-Method Generator (PMG), which generates PMs automatically according to a naive user's requests. One algorithm of PMG uses numerical access relevance between pairs of classes as a guide for the traversal of an OODB schema. In this paper we define the notion of access relevance to measure the significance of the (indirect) connection between any two classes in an OODB and present efficient algorithms to compute access relevance. The manual PM generation in an interoperable multi object-oriented database (IM-OODB) is even more difficult than for one OODB since a user has to be familiar with several OODBs. We use a hierarchical approach for developing efficient online algorithms for the computation of access relevances in an IM-OODB, based on precomputed access relevances for each autonomous OODB. In an IM-OODB the access relevances are used as a guide in generating PMs between the classes of different OODBs.     

UML在高校财务绩效管理系统设计中的应用

统一建模语言UML(Unified Modeling Language)是面向对象软件开发方法的重要技术.在对UML进行了简要的介绍和概括后,结合财务绩效管理模型实例,对UML的技术进行了研究.在对系统进行需求分析的基础上,采用建模工具构建了系统的用户需求模型、对象结构模型和行为模型,对面向对象软件项目的开发具有一定的指导作用.     

A structure-function-control paradigm for knowledge-based modeling and design of manufacturing workcells

This paper discusses the integration of structural, functional and control knowledge in manufacturing workcell modeling, simulation and design. After an overview of applications of semantic and object-oriented data models in the manufacturing domain, issues relating to the control synthesis for manufacturing workcells are presented. In particular, a data model encompassing functional and control features, along with application domain structural knowledge, is developed. This model assists in explicitly representing the control aspects of engineering design within an object-oriented database and supports a task-level, functionality-driven, manufacturing workcell design. Since manufacturing workcells consist of a number of elements interacting in a complex manner, workcell control design is one of the most difficult steps in the workcell design procedure. Message passage, commonly used in object-oriented databases, provides no explicit modeling of the database behavior. Hence, it can not serve as a tool for the design of system control. On the other hand, Petrinets (PN) have proven successful in describing complex interaction among active agents. This paper will explore the incorporation of Petri nets as a basis for describing application control knowledge within a structure-function-control data model.     

Performance evaluation of the object-relational transformation methodology

The emergence of the object-oriented (OO) methodology has shown its capabilities in modelling the real world better than the earlier relational methodology. However, object-oriented databases (OODBs) are still considered immature in comparison with relational databases (RDBs) which have existed for many years. RDBs still continue to dominate the implementation of databases constituting more than 90% of all database implementations [28]. It was felt worthwhile to exploit the great modelling power of OO methodology, while still facilitating relational implementations. These reasons have led us to develop an object-relational transformation methodology [20, 21, 22, 23, 24 and 25] which allows us to use the OO methodology for data modelling and to transform it into a relational logical model for implementation in relational database management systems (RDBMSs). The main purpose of this paper is to present a performance evaluation of the transformation methodology. The evaluation covers I/O cost models of different types of queries. The type of evaluation is basically comparison-based, in which the performance of SQL operations upon a set of tables derived from the relational data model is compared with the tables derived from the OO data model using the transformation methodology. The results of the evaluation show that the performance of the RDB implementation transferred from an OO conceptual model using our object-relational transformation methodology is better than the relational implementation using a conventional relational modelling. Moreover, in many cases, the relational modelling is not applicable since it cannot capture the design semantics particularly relating to collection types. Our object-relational methodology solves this problem.     

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.     

基于Web的智能化作业系统研究

本文设计了智能化作业系统的工作模型及其层次结构:采用学习者需求驱动模式,并采用四层模型层次结构来实现,数据层、网络服务层和用户类型表现层和个性化表现层;本系统的数据库设计应用了基于关系数据库的面向对象理论,方便了信息的获得,同时提高了系统的可扩展性。     

基于Web的智能化作业系统研究

本文设计了智能化作业系统的工作模型及其层次结构：采用学习者需求驱动模式,并采用四层模型层次结构来实现,数据层、网络服务层和用户类型表现层和个性化表现层;本系统的数据库设计应用了基于关系数据库的面向对象理论,方便了信息的获得,同时提高了系统的可扩展性。     

Efficient Query Execution Techniques in a 4DIS Video Database System for eLearning

In this paper, we describe our work on developing an eLearning video database system. The eLearning video database provides a temporal modeling framework for describing eLearning video data and it supports data distribution by applying vertical class partitioning techniques. Building on top of our previous work on Four Dimensional Information System (4DIS)—an object-oriented temporal modeling framework, we apply vertical class partitioning techniques onto a 4DIS eLearning video database system as a means for efficient query execution. We further describe our work on dynamic fetching of multimedia eLearning video on the Internet. A detailed cost model for query execution through vertical class partitioning is developed. Finally, we demonstrate through the use of a running example the effectiveness of our vertical class partitioning approach.     

Global ridge orientation modeling for partial fingerprint identification

Identifying incomplete or partial fingerprints from a large fingerprint database remains a difficult challenge today. Existing studies on partial fingerprints focus on one-to-one matching using local ridge details. In this paper, we investigate the problem of retrieving candidate lists for matching partial fingerprints by exploiting global topological features. Specifically, we propose an analytical approach for reconstructing the global topology representation from a partial fingerprint. First, we present an inverse orientation model for describing the reconstruction problem. Then, we provide a general expression for all valid solutions to the inverse model. This allows us to preserve data fidelity in the existing segments while exploring missing structures in the unknown parts. We have further developed algorithms for estimating the missing orientation structures based on some a priori knowledge of ridge topology features. Our statistical experiments show that our proposed model-based approach can effectively reduce the number of candidates for pair-wised fingerprint matching, and thus significantly improve the system retrieval performance for partial fingerprint identification.     

The study of indexing techniques on object oriented databases

An object-oriented database (OODB) has been becoming more important in recent years. It can deal with a large amount of complex objects and relationships that relational database (RDB) systems cannot handle well. However, the retrieval and update performance of an OODB depends on indexing techniques. In this paper, we study the indexing techniques on OODBs, based on an inheritance hierarchy and an aggregation hierarchy. Given the access probability and the size of each class, we propose a cost function to evaluate the gain of building an index on an inheritance hierarchy. For an aggregation hierarchy, we use a path-catenation technique to evaluate how to build index files on classes. Through some experiments, we found our methods have better retrieval performance than most ones proposed before.     

Efficient and flexible access control via Jones-optimal logic program specialisation

We describe the use of a flexible meta-interpreter for performing access control checks on deductive databases. The meta-program is implemented in Prolog and takes as input a database and an access policy specification. For processing access control requests we specialise the meta-program for a given access policy and database by using the logen partial evaluation system. The resulting specialised control checking program is dependent solely upon dynamic information that can only be known at the time of actual access request evaluation. In addition to describing our approach, we give a number of performance measures for our implementation of an access control checker. In particular, we show that by using our approach we get flexible access control with virtually no overhead, satisfying the Jones optimality criterion. The paper also shows how to satisfy the Jones optimality criterion more generally for interpreters written in the non-ground representation.     

Optimizing database architecture for the new bottleneck: memory access

In the past decade, advances in the speed of commodity CPUs have far out-paced advances in memory latency. Main-memory access is therefore increasingly a performance bottleneck for many computer applications, including database systems. In this article, we use a simple scan test to show the severe impact of this bottleneck. The insights gained are translated into guidelines for database architecture, in terms of both data structures and algorithms. We discuss how vertically fragmented data structures optimize cache performance on sequential data access. We then focus on equi-join, typically a random-access operation, and introduce radix algorithms for partitioned hash-join. The performance of these algorithms is quantified using a detailed analytical model that incorporates memory access cost. Experiments that validate this model were performed on the Monet database system. We obtained exact statistics on events such as TLB misses and L1 and L2 cache misses by using hardware performance counters found in modern CPUs. Using our cost model, we show how the carefully tuned memory access pattern of our radix algorithms makes them perform well, which is confirmed by experimental results. Received April 20, 2000 / Accepted June 23, 2000     

The impact of programming paradigms on the efficiency of an individual-based simulation model

We look in detail at an individual-based simulation of the spread of barley yellow dwarf virus. The need for a very large number of individual plants and aphids along with multiple runs using different model parameters mean that it is important to keep memory and processor requirements within reasonable bounds. We present implementations of the model in both imperative and object-oriented programming languages, particularly noting aspects relating to ease of implementation and runtime performance. Finally, we attempt to quantify the cost of some of the decisions made in terms of their memory and processor time requirements.     

Optimizing main-memory join on modern hardware

In the past decade, the exponential growth in commodity CPU's speed has far outpaced advances in memory latency. A second trend is that CPU performance advances are not only brought by increased clock rates, but also by increasing parallelism inside the CPU. Current database systems have not yet adapted to these trends and show poor utilization of both CPU and memory resources on current hardware. In this paper, we show how these resources can be optimized for large joins and translate these insights into guidelines for future database architectures, encompassing data structures, algorithms, cost modeling and implementation. In particular, we discuss how vertically fragmented data structures optimize cache performance on sequential data access. On the algorithmic side, we refine the partitioned hash-join with a new partitioning algorithm called "radix-cluster", which is specifically designed to optimize memory access. The performance of this algorithm is quantified using a detailed analytical model that incorporates memory access costs in terms of a limited number of parameters, such as cache sizes and miss penalties. We also present a calibration tool that extracts such parameters automatically from any computer hardware. The accuracy of our models is proven by exhaustive experiments conducted with the Monet database system on three different hardware platforms. Finally, we investigate the effect of implementation techniques that optimize CPU resource usage. Our experiments show that large joins can be accelerated almost an order of magnitude on modern RISC hardware when both memory and CPU resources are optimized     

Adaptive caching and refreshing in mobile databases

The mobile computing environment is receiving increasing attention recently. We consider a mobile environment in which a collection of mobile clients accesses a stationary database server via a wireless channel. Due to the limited bandwidth of a wireless channel and the instability of the wireless network, caching of frequently accessed data items in a client's local storage becomes especially important for improving the performance and data availability of data access queries. In this paper, we discuss the limitations of existing caching mechanisms in a mobile environment and investigate issues that need to be addressed. We propose an adaptive caching model that could cope with the nature of a mobile environment and the low-bandwidth wireless media, supporting fast data access. We describe the adaptive cache replacement and refresh mechanisms; explain the implementation in the context of object-oriented databases; and illustrate the results of some exploratory experiments to demonstrate the feasibility of the mechanisms.     

Design and Query Strategies to Hypermedia Applications

In this paper we propose an object-oriented model for designing hypermedia applications. As the object-oriented paradigm allows complex and user-defined types, nonconventional and nonatomic attributes, we can take advantage of these capabilities, not only for information modelling, but also for providing alternative ways for accessing information.A query language is then presented; it is based on an Object-Oriented Database System query language. It combines features of object-oriented databases queries and primitives for hypermedia navigation. The language offers the possibility of querying both the application-domain information, and allowing the designers to obtain information about the schema of the application.We present some examples of the use of the object-oriented model and the query language.     

The OODB path-method generator (PMG) using access weights and precomputed access relevance

A path-method is used as a mechanism in object-oriented databases (OODBs) to retrieve or to update information relevant to one class that is not stored with that class but with some other class. A path-method is a method which traverses from one class through a chain of connections between classes and accesses information at another class. However, it is a difficult task for a casual user or even an application programmer to write path-methods to facilitate queries. This is because it might require comprehensive knowledge of many classes of the conceptual schema that are not directly involved in the query, and therefore may not even be included in a user's (incomplete) view about the contents of the database. We have developed a system, called path-method generator (PMG), which generates path-methods automatically according to a user's database-manipulating requests. The PMG offers the user one of the possible path-methods and the user verifies from his knowledge of the intended purpose of the request whether that path-method is the desired one. If the path method is rejected, then the user can utilize his now increased knowledge about the database to request (with additional parameters given) another offer from the PMG. The PMG is based on access weights attached to the connections between classes and precomputed access relevance between every pair of classes of the OODB. Specific rules for access weight assignment and algorithms for computing access relevance appeared in our previous papers [MGPF92, MGPF93, MGPF96]. In this paper, we present a variety of traversal algorithms based on access weights and precomputed access relevance. Experiments identify some of these algorithms as very successful in generating most desired path-methods. The PMG system utilizes these successful algorithms and is thus an efficient tool for aiding the user with the difficult task of querying and updating a large OODB. Received July 19, 1993 / Accepted May 16, 1997     

An evaluation of vertical class partitioning for query processing in object-oriented databases

Vertical partitioning is a design technique for reducing the number of disk accesses to execute a given set of queries by minimizing the number of irrelevant instance variables accessed. This is accomplished by grouping the frequently accessed instance variables as vertical class fragments. The complexity of object-oriented database models due to subclass hierarchy and class composition hierarchy complicates the definition and representation of vertical partitioning of the classes, which makes the problem of vertical partitioning in OODBs very challenging. In this paper, we develop a comprehensive analytical cost model for processing of queries on vertically partitioned OODB classes. A set of analytical evaluation results is presented to show the effect of vertical partitioning, and to study the trade-off between the projection ratio versus selectivity factor vis-a-vis sequential versus index access. Furthermore, an empirical experimental prototype supporting vertical class partitioning has been implemented on a commercial OODB tool kit to validate our analytical cost model.     

MODEC: A Multi-Granularity Mobile Object-Oriented Database Caching Mechanism, Prototype and Performance

An inherent limitation in mobile data access is due to the unreliable and low bandwidth wireless communication channel. Caching of useful database items from database server in local storage of mobile clients is effective in reducing data access latency and wireless bandwidth consumption. In the event of disconnection, cached data can also serve the purpose of partial query processing. In this paper, we present the implementation and evaluate a new caching mechanism for object-oriented database systems in a mobile environment called MODEC. MODEC possesses the capabilities of performing caching at multiple granularities and adapting to changes in data access pattern, providing improved performance through tolerating limited inconsistency to read-only transactions. This caching capabilities is supported via standard ODMG modeling constructs. The prototype of MODEC is implemented using ODE database. Empirical system performance results are obtained from experiments on the prototype with data from a real-life database. The results are validated against results obtained via detailed simulation studies on MODEC. Both sets of results are found to be consistent and are in favor of our MODEC mechanism in providing a feasible solution to the mobile data access problem under the constraints in a mobile environment.