时态多维模型设计

传统的数据仓库基于维度时不变的观点,只考虑事实随时间的变化.实际上,数据仓库的多维模式是随时间缓慢变化的.数据仓库多维模式的变化会影响OLAP查询结果的正确性,有必要对多维模式的历史变化进行维护.在分析多维模型结构的基础上,对多维模式的元素进行时态扩展,给出了一种能解决复杂多维结构的时态多维模型的形式定义,并对时态模型更新操作的实现进行了分析,最后对时态模型各元素应满足的时间一致性约束进行了分析.     

Schema evolution of an object-oriented real-time database systemfor manufacturing automation

Database schemata often experience considerable changes during the development and initial use phases of database systems for advanced applications such as manufacturing automation and computer-aided design. An automated schema evolution system can significantly reduce the amount of effort and potential errors related to schema changes. Although schema evolution for nonreal-time databases was the subject of previous research, its impact on real-time database systems remains unexplored. These advanced applications typically utilize object-oriented data models to handle complex data types. However, there exists no agreed-upon real-time object-oriented data model that can be used as a foundation to define a schema-evolution framework. Therefore, the authors first design a conceptual real-time object-oriented data model, called Real-time Object Model with Performance Polymorphism (ROMPP). It captures the key characteristics of real-time applications-namely, timing constraints and performance polymorphism-by utilizing specialization-dimension and letter-class hierarchy constructs, respectively. They then re-evaluate previous (nonreal-time) schema evolution support in the context of real-time databases. This results in modifications to the semantics of schema changes and to the needs of schema change resolution rules and schema invariants. Furthermore, they expand the schema change framework with new constructs-including new schema change operators, new resolution rules, and new invariants-necessary for handling the real-time characteristics of ROMPP     

点击流数据仓库中客户管理星型模式设计

点击流数据仓库中存储了大量客户基本信息及客户在网站上的点击行为信息,其组织方式的好坏直接影响到联机分析处理和数据挖掘的效率.传统的页面事件和会话星型模式没有把客户这一商业行为中的核心实体作为实事表,因而不能提供直接面向客户的综合分析.对原有模式进行分析的基础上,根据企业CRM的实际需求,提出了一种以客户为中心的客户管理星型模式,并利用面向客户的时间轮转模型予以实现.     

Techniques for process model evolution in EPOS

The authors categorize some aspects of software process evolution and customization, and describe how they are handled in the EPOS PM system. Comparisons are made to other PM systems. A process model in EPOS consists of a schema of classes and meta-classes, and its model entities and relationships. There is an underlying software engineering database, EPOSDB, offering uniform versioning of all model parts and a context of nested cooperating transactions. Then, there is a reflective object-oriented process specification language, on top of the EPOSDB. Policies for model creation, composition, change, instantiation, refinement, and enaction are explicitly represented and are used by a set of PM automatic tools. The main tools are a planner to instantiate tasks, an execution manager to enact such tasks, and a PM manager to define, analyze, customize, and evolve the process schema     

Comparing the understandability of alternative data warehouse schemas: An empirical study

An easily understood data warehouse model enables users to better identify and retrieve its data. It also makes it easier for users to suggest changes to its structure and content. Through an exploratory, empirical study, we compared the understandability of the star and traditional relational schemas. The results of our experiment contradict previous findings and show schema type did not lead to significant performance differences for a content identification task. Further, the relational schema actually led to slightly better results for a schema augmentation task. We discuss the implications of these findings for data warehouse design and future research.     

Version management for business process schema evolution

The current business environment changes rapidly, dictated by user requirements and market opportunities. Organisations are therefore driven to continuously adapt their business processes to new conditions. Thus, management of business process schema evolution, particularly process version control, is in great demand to capture the dynamics of business process schema changes. This paper aims to facilitate version control for business process schema evolution, with an emphasis on version compatibility, co-existence of multiple versions and dynamic version shifts. A multi-level versioning approach is established to specify dependency between business process schema evolutions, and a novel version preserving graph model is proposed to record business process schema evolutions. A set of business process schema updating operations is devised to support the entire set of process change patterns. By maintaining sufficient and necessary schema and version information, our approach provides comprehensive support for navigating process instance executions of different and changing versions, and deriving the process schema of a certain version. A prototype is also implemented for the proof-of-concept purpose.     

Preserving mapping consistency under schema changes

In dynamic environments like the Web, data sources may change not only their data but also their schemas, their semantics, and their query capabilities. When a mapping is left inconsistent by a schema change, it has to be detected and updated. We present a novel framework and a tool (ToMAS) for automatically adapting (rewriting) mappings as schemas evolve. Our approach considers not only local changes to a schema but also changes that may affect and transform many components of a schema. Our algorithm detects mappings affected by structural or constraint changes and generates all the rewritings that are consistent with the semantics of the changed schemas. Our approach explicitly models mapping choices made by a user and maintains these choices, whenever possible, as the schemas and mappings evolve. When there is more than one candidate rewriting, the algorithm may rank them based on how close they are to the semantics of the existing mappings.Received: 13 January 2004, Accepted: 26 March 2004, Published online: 12 August 2004Edited by: M. Carey     

Schema evolution: Concepts, terminology, and solutions

Most applications must keep objects from one session to the next. This is known as persistence. But objects are not raw data: They are instances of classes. What happens if an object's class (its generator) changes from one session to the next? This problem is known as schema evolution (the term schema is borrowed from relational databases). This column defines a framework for addressing schema evolution in object technology     

Enriching the ER model based on discovered association rules

The entity-relationship (ER) model, a powerful means for business and data modeling, needs to be enriched with new semantics as the real world changes and its understanding improves. This paper attempts at enriching the ER model based on association rules (AR) discovered from large databases by introducing specializations and sub-types into the ER model. The proposed framework is extended to deal with more general, flexible and linguistic knowledge in fuzzy association rules. Moreover, transforming an AR-enriched-ER (AR-EER) schema to a relational database (RDB) schema is also investigated.     

Schema manipulation in self-describing and self-documenting data models

This paper integrates data, schema and meta-schema into a uniform model and provides one data language to manipulate and modify both data and schema. The modifications on the schema are then propagated to the schema's extension via propagation rules. The integration and the schema modification are all developed within the framework of self-describing and self-documenting models of data and they are fundamental in capturing the evolution of the database, which includes not only data changes, but schema changes as well.This work has been partially supported by NASA under contract NAS 5-26810.     

基于模式图的规范化XML模式设计

在给定关系模式的属性集及其函数依赖最小覆盖集的基础上,提出一种基于模式图的规范化XML模式设计方法。定义了模式图,在模式图中增加了Keys的描述信息,给出由函数依赖集构造模式图的算法。该模式图独立于具体的XML模式语言,经分析证明,所设计的模式满足XNF。     

A transparent schema-evolution system based on object-oriented viewtechnology

When a database is shared by many users, updates to the database schema are almost always prohibited because there is a risk of making existing application programs obsolete when they run against the modified schema. The paper addresses the problem by integrating schema evolution with view facilities. When new requirements necessitate schema updates for a particular user, then the user specifies schema changes to his personal view, rather than to the shared base schema. Our view schema evolution approach then computes a new view schema that reflects the semantics of the desired schema change, and replaces the old view with the new one. We show that our system provides the means for schema change without affecting other views (and thus without affecting existing application programs). The persistent data is shared by different views of the schema, i.e., both old as well as newly developed applications can continue to interoperate. The paper describes a solution approach of realizing the evolution mechanism as a working system, which as its key feature requires the underlying object oriented view system to support capacity augmenting views. We present algorithms that implement the complete set of typical schema evolution operations as view definitions. Lastly, we describe the transparent schema evolution system (TSE) that we have built on top of GemStone, including our solution for supporting capacity augmenting view mechanisms     

Decentralized control and identified-model predictive control of divided wall columns

As a thermal separation method, distillation is one of the most important separation technologies in the chemical industry. Given its importance, it is no surprise that increasing efforts have been made in reducing its energy inefficiencies. A great deal of research is focused in the design and optimization of the divided-wall column (DWC). Its applications are still reduced due to distrust of its controllability and robustness. Previous references have studied the decentralized control of DWC but still few papers deal about model predictive control (MPC) applied to DWC.In this work we present a decentralized control of both a divided-wall column along with its equivalent MPC schema, both approaches are compared. Instead of building a rigorous model or performing the step test to an existing plant, the MPC model is obtained by identification of a rigorous simulation. An ARX model is demonstrated to represent adequately the DWC column behavior. This approach might be very convenient if plant testing is not available.     

A runtime approach to model-generic translation of schema and data

To support heterogeneity is a major requirement in current approaches to integration and transformation of data. This paper proposes a new approach to the translation of schema and data from one data model to another, and we illustrate its implementation in the tool MIDST-RT.We leverage on our previous work on MIDST, a platform conceived to perform translations in an off-line fashion. In such an approach, the source database (both schema and data) is imported into a repository, where it is stored in a universal model. Then, the translation is applied within the tool as a composition of elementary transformation steps, specified as Datalog programs. Finally, the result (again both schema and data) is exported into the operational system.Here we illustrate a new, lightweight approach where the database is not imported. MIDST-RT needs only to know the schema of the source database and the model of the target one, and generates views on the operational system that expose the underlying data according to the corresponding schema in the target model. Views are generated in an almost automatic way, on the basis of the Datalog rules for schema translation.The proposed solution can be applied to different scenarios, which include data and application migration, data interchange, and object-to-relational mapping between applications and databases.     

Managing schema evolution in a container‐based persistent system

Managing schema evolution is a problem every persistent system has to cope with to be useful in practice. Schema evolution consists basically of supporting class modification and dealing with data objects created and stored under the old class definitions. Several proposals have been made to handle this problem in systems that follow a full orthogonally persistent approach, but, until now, there has not been any proposal to support it in container‐based persistent systems. In this paper we describe a schema evolution management system designed for Barbados. Barbados is a complete programming environment which is based on an architecture of containers to provide persistent storage. Barbados does not provide full orthogonal persistence, but, as will be described in this paper, its architecture has several other advantages. Among them is the fact that this model is especially suitable for solving the schema evolution problem. Copyright © 2002 John Wiley & Sons, Ltd.     

基于IDEFlx的面向对象XML建模

为了在IDEFlx数据库模型和面向对象模型的XML文档之间共享统一的模型，提出并实现了一种基于IDEFlx模型的面向对象XML建模方法。根据IDEFlx方法建立数据库模型，得到该模型的XML文档，然后对XML文档进行解析和重新组合，转换成为面向对象模型，并且生成该模型的XMLSchema文档。     

Modeling dynamic relationship types for subsets of entity type instances and across entity types

In a traditional ER model, once we specify a subclass or superclass relationship, any changes to that relationship are treated as schema evolution. Further, ER models are rigid in the sense that once a relationship type is specified across a set of entity types, an instance of relationship type occur when one instance of all participating entity types are specified. Therefore, it is difficult to introduce in a simplified manner all relationship types across subsets of given set of entity types. In this paper, we provide mechanisms to model in our extended ER model: (i) specification of dynamic relationship types across subsets of instances of entity types, (ii) a simplified specification of relationships across subsets of given set of entity types, and (iii) mapping our extended ER model to relational database schema. We also show through an e-contract example the utility of our extended ER model.     

Neurophysiological correlates in interface design: An HCI perspective

Objective: The current study examines the changes in functional connectivity that occurs when expert users adapt to an alternate mapping. Background: Research has indicated that interfaces that are similar will result in more errors and may contribute to confusion. Methods: Six volunteers were recruited to determine the neurophysiological changes that occur when users are exposed to an alternate mapping once an internal mental model is formed. Results: The results indicated a change in synchronization after alterations to the button mappings occurred. By altering the layout or order of the task, a difference in the activation pattern was observed. New areas became synchronized while synchronized activity that was present in the developed internal model became desynchronized. Altering the complexity of the task resulted in different patterns of activation recorded on the quantitative electroencephalogram (QEEG). Conclusion: Users often form a schema when learning a device and subsequent interactions are compared to the mental model formed during the initial learning phase. If the newer interface differs significantly a new schema is formed, resulting in a different pattern of synchronization recorded on the QEEG. Application: The use of this knowledge can assist in the development of new interfaces. If the intent is to create a similar interface design, the activation pattern should remain the same indicating that the old schema can be applied. An interface that displays a different cognitive pattern will indicate that a new schema was developed.