Semantics of OCL specified with QVT

The Object Constraint Language (OCL) has been for many years formalized both in its syntax and semantics in the language standard. While the official definition of OCL’s syntax is already widely accepted and strictly supported by most OCL tools, there is no such agreement on OCL’s semantics, yet. In this paper, we propose an approach based on metamodeling and model transformations for formalizing the semantics of OCL. Similarly to OCL’s official semantics, our semantics formalizes the semantic domain of OCL, i.e. the possible values to which OCL expressions can evaluate, by a metamodel. Contrary to OCL’s official semantics, the evaluation of OCL expressions is formalized in our approach by model transformations written in QVT. Thanks to the chosen format, our semantics definition for OCL can be automatically transformed into a tool, which evaluates OCL expressions in a given context. Our work on the formalization of OCL’s semantics resulted also in the identification and better understanding of important semantic concepts, on which OCL relies. These insights are of great help when OCL has to be tailored as a constraint language of a given DSL. We show on an example, how the semantics of OCL has to be redefined in order to become a constraint language in a database domain.

扩展QVT Relations实现业务流程模型的转换

QVT(Query/View/Transformation)Relations无法描述包含嵌套模式,因此在描述流程模型的转换规则时存在一些困难.针对此问题,对QVT Relations 进行了扩展,引入了模式因子、嵌套关系表达式和关联端约束这3个概念,并讨论了扩充之后匹配模型和创建模型的语义变化.并用一个例子展示,扩展...     

Case-based exploration of bidirectional transformations in QVT Relations

QVT Relations (QVT-R), a standard issued by the Object Management Group, is a language for the declarative specification of model transformations. This paper focuses on a particularly interesting feature of QVT-R: the declarative specification of bidirectional transformations. Rather than writing two unidirectional transformations separately, a transformation developer may provide a single relational specification which may be executed in both directions. This approach saves specification effort and ensures the consistency of forward and backward transformations. This paper explores QVT-R’s support for bidirectional model transformations through a spectrum of transformation cases. The transformation cases vary with respect to several factors such as the size of the transformation definition or the relationships between the metamodels for source and target models. The cases are solved in QVT-R, but may be applied to other bidirectional transformation languages, as well; thus, they may be used as a benchmark for comparing bidirectional transformation languages. In our work, we focus on the following research questions: functionality of bidirectional transformations in terms of relations between source and target models, solvability (which problems may be solved by a single relational specification of a bidirectional transformation), variability (does a bidirectional transformation contain varying elements, i.e., elements being specific to one direction), comprehensibility (referring to the ease of understanding and constructing QVT-R transformations), and the semantic soundness of bidirectional transformations written in QVT-R.     

基于QVT模型转换的研究

模型转换是MDA(Model Driven Architecture)的核心技术之一,也是目前MDA研究的热点.查询/视图/转换(QVT)是OMG(Object Management Group)提出的模型转换的标准化方案.介绍编织和已有的各种模型转换技术,以及这些技术存在的缺点.同时介绍了基于QVT的模型驱动构架和属性结构,从而满足一致性和消解的要求.在语言维上,对QVT的三种语言分别进行了介绍,并根据规则实现了关系到核心语言的转换.FMTP系统基于QVT规范和Kermeta语言中的模型转换功能,通过对QVT核心分层,设计了基于映射的四层QVT结构的模型转换工具.     

QVT的模型转换方法的研究

模型转换是MDA中最重要的部分之一,其性能的好坏直接影响到软件开发工作的进行.介绍了模型、计算无关模型、平台无关模型、平台相关模型、模型转换和转换规则等的理论知识.其次通过对目前比较流行的直接转换方法、基于关系代数的转换方法和基于元模型间映射的转换方法等模型转换方法的研究,分析了其存在的不足之处,并且提出了QVT的模型转换方法.研究结果表明,文中提出的方法具有很大的性能优势.     

A simple game-theoretic approach to checkonly QVT Relations

The QVT Relations (QVT-R) transformation language allows the definition of bidirectional model transformations, which are required in cases where two (or more) models must be kept consistent in the face of changes to either or both. A QVT-R transformation can be used either in checkonly mode, to determine whether a target model is consistent with a given source model, or in enforce mode, to change the target model. A precise understanding of checkonly mode transformations is prerequisite to a precise understanding of enforce mode transformations, and this is the focus of this paper. In order to give semantics to checkonly QVT-R transformations, we need to consider the overall structure of the transformation as given by when and where clauses, and the role of trace classes. In the standard, the semantics of QVT-R are given both directly, and by means of a translation to QVT Core, a language which is intended to be simpler. In this paper, we argue that there are irreconcilable differences between the intended semantics of QVT-R and those of QVT Core, so that no translation from QVT-R to QVT Core can be semantics-preserving, and hence no such translation can be helpful in defining the semantics of QVT-R. Treating QVT-R directly, we propose a simple game-theoretic semantics. We demonstrate its behaviour on examples and show how it can be used to prove an example result comparing two QVT-R transformations. We demonstrate that consistent models may not possess a single trace model whose objects can be read as traceability links in either direction. We briefly discuss the effect of variations in the rules of the game, to elucidate some design choices available to the designers of the QVT-R language.     

基于QVT的模型转换方法研究

针对不同模式之间规则不能重用甚至无法描述嵌套模式的问题．提出一种基于扩展MOF元模型与扩展QVT语言相结合的模型转换方法。该方法通过扩展MOF元模型解决模型之间规则不能重用问题．通过扩展QVTRelations可以增强规则语言的有效性,为模型建立和模型转换提供一种更有效的途径。在一个股票交易系统的转换应用实例中验证该方法的正确性。     

Development of Secure XML Data Warehouses with QVT

ContextData warehouses are systems which integrate heterogeneous sources to support the decision making process. Data from the Web is becoming increasingly more important as sources for these systems, which has motivated the extensive use of XML to facilitate data and metadata interchange among heterogeneous data sources from the Web and the data warehouse. However, the business information that data warehouses manage is highly sensitive and must, therefore, be carefully protected. Security is thus a key issue in the design of data warehouses, regardless of the implementation technology. It is important to note that the idiosyncrasy of the unstructured and semi-structured data requires particular security rules that have been specifically tailored to these systems in order to permit their particularities to be captured correctly. Unfortunately, although security issues have been considered in the development of traditional data warehouses, current research lacks approaches with which to consider security when the target platform is based on XML technology.ObjectiveWe shall focus on defining transformations to obtain a secure XML Schema from the conceptual multidimensional model of a data warehouse.MethodWe have first defined the rationale behind the transformation rules and how they have been developed in natural language, and we have then established them clearly and formally by using the QVT language. Finally, in order to validate our proposal we have carried out a case study.ResultsWe have proposed an approach for the model driven development of Secure XML Data Warehouses, defining a set of QVT transformation rules.ConclusionThe main benefit of our proposal is that it is possible to model security requirements together with the conceptual model of the data warehouse during the early stages of a project, and automatically obtain the corresponding implementation for XML.     

Bidirectional model transformations in QVT: semantic issues and open questions

We consider the OMG’s queries, views and transformations standard as applied to the specification of bidirectional transformations between models. We discuss what is meant by bidirectional transformations, and the model-driven development scenarios in which they are needed. We analyse the fundamental requirements on tools which support such transformations, and discuss some semantic issues which arise. In particular, we show that any transformation language sufficient to the needs of model-driven development would have to be able to express non-bijective transformations. We argue that a considerable amount of basic research is needed before suitable tools will be fully realisable, and suggest directions for this future research.     

一种模型转换分类方法及其在QVT中的应用

针对模型驱动的软件开发过程中潜在的交互性和一致性问题,介绍了一种模型转换分类的方法MTCM.根据模型和模型所描述的系统以及使用的建模语言的不同对模型转换进行细粒度的分类,然后按照此分类方法对OMG组织提出的模型转换标准QVT(查询/视图/转换)进行研究,并通过一个经典的模型转换实例即从UML模型到RDBMS模型的转换进行验证.分析得出结论,MTCM方法有助于提高模型转换的准确性和高效性.     

基于可集成性的细粒度结构演化

软件结构为达到软件系统质量属性的一种手段，对于基于可集成性的软件结构研究，提出小粒度结构演化（FGSAE，Fine-Grained Architectural Evolution)，改变既有系统的软件结构，增加模块独立性，显示表达可集成性的模块接口，满足质量属性需求，为黑盒开发策略的大粒度复用做预备，可以延伸软件功能，延长软件生命周期，达到提高开发效益的目的，以2个相关概念模型－软件结构（Software Architecture,SA），FGSAE，说明FGSAE如何指导软件变换，满足可集成性的需求，并提出关键活动内容，最后以一个成功的案例，即在Internet上运行的西洋棋艺游戏系统，验证FGSAE的有效性。     

嵌入式系统开发中的设计模式

嵌入式系统的广泛应用促使嵌入式系统软件开发者采用设计模式等先进技术来改善现有的软件开发方法。针对嵌入式系统软件的实际特性，提出在嵌入式软件开发中应用设计模式技术。首先对嵌入式系统软件开发现状及设计模式技术进行分析，然后详细讨论了设计模式技术在嵌入式系统软件开发中的应用过程。最后通过一个例子来阐述该方法的优越性。     

Detecting and repairing anomalous evolutions in noisy environments

In systems where agents are required to interact with a partially known and dynamic world, sensors can be used to obtain knowledge about the environment. However, sensors may be unreliable, that is, they may deliver wrong information (due, e.g., to hardware or software malfunctioning) and, consequently, they may cause agents to take wrong decisions, which is a scenario that should be avoided. The paper considers the problem of reasoning in noisy environments in a setting where no (either certain or probabilistic) data is available in advance about the reliability of sensors. Therefore, assuming that each agent is equipped with a background theory encoding its general knowledge about the world, a concept of detecting an anomaly perceived in sensor data and the related concept of agent recovering to a coherent status of information are defined. In this context, the complexities of various anomaly detection and anomaly recovery problems are studied. Finally, rewriting algorithms are proposed that transform recovery problems into equivalent inference problems under answer set semantics, thereby making them effectively realizable on top of available answer set solvers.     

面向分布式系统的设计模式

提出一种面向分布式系统的命令模式.设计了此模式的高层框架,框架中引入了命令总线和命令执行器等组件.根据此框架,设计了此模式的结构类图,阐述了它各组成部分的具体功能,分析了命令在此模式中的执行流程.基于这种模式,开发者在设计命令类时无须考虑将命令对象序列化,传送给服务端,也不必考虑如何从服务端接收数据并将它们反序列化.结论表明此模式屏蔽了分布式环境的通信复杂性,让使用者能以网络透明的方式按原有习惯使用命令模式.     

Sense-making strategies in explorative intelligence analysis of network evolutions

Visualising how social networks evolve is important in intelligence analysis in order to detect and monitor issues, such as emerging crime patterns or rapidly growing groups of offenders. It remains an open research question how this type of information should be presented for visual exploration. To get a sense of how users work with different types of visualisations, we evaluate a matrix and a node-link diagram in a controlled thinking aloud study. We describe the sense-making strategies that users adopted during explorative and realistic tasks. Thereby, we focus on the user behaviour in switching between the two visualisations and propose a set of nine strategies. Based on a qualitative and quantitative content analysis we show which visualisation supports which strategy better. We find that the two visualisations clearly support intelligence tasks and that for some tasks the combined use is more advantageous than the use of an individual visualisation.     

FT＆MEDB服务器的工作模式设计

在讨论数据库服务器结构的基础上,根据FT＆MEDB系统结构设计方案,给出了FT＆MEDB服务器的工作模式设计,在所设计的工作模式下,给出了服务器与客户端的连接方式,并简明阐述了FT＆MEDB系统所选用的应用服务器体系结构。     

Design pattern recovery based on annotations

Design patterns have been widely used for developing flexible, extensible and perceptible applications to produce effective, reliable, verifiable and easily maintained software systems. The main advantage of using patterns is to take the edge of using best practices and experiences of others in solving the challenging tasks. Patterns have been extensively tested in different applications and reusing them yields the quality software. In this paper, we present a design pattern recovery approach based on annotations, regular expressions and database queries. We define the varying features of patterns and apply rules to match these features with the source code elements. Our novel approach reduces the search space and time for detecting patterns by using appropriate semantics of annotations from large legacy systems. We have tested our approach as proof of concept on motivating examples, and the obtained results are very encouraging.     

Program reversals for evolutions with non-uniform step costs

The reversal of a program execution can be helpful for several purposes. The reverse mode of automatic differentiation, parameter estimation, and debugging represent some of the tasks that may require the intermediate values of a calculation in reverse order. The recording of a complete execution log forms the simplest approach to providing the data required for the reversal. However, this store-everything method causes an enormous demand for memory. The generation of the execution log piece by piece offers the possibility to reduce the storage requirement. To that end the forward calculation is restarted from suitably placed checkpoints leading to a more or less complicated reversal schedule.This paper deals with the reversal of evaluation procedures that consist of a sequence of time steps with varying computational complexity. We present a new search algorithm for determining a reversal schedule that minimizes the runtime of the reversal process for a given number of checkpoints. By exploiting a certain monotonicity property, the search algorithm based on dynamic programming can be made to grow only quadratically with the number of time steps to be reverted. We report the runtime savings that can be achieved performing the reversal with an optimal, i.e. time-minimal, reversal schedule for a test problem based on Burgers equation.Received: 30 November 2001, Revised: 13 October 2003, Published online: 16 December 2003