Statechart Modeling with Fujaba

This paper is a small case study on a simple visual language. We use the Fujaba approach to exemplify, how the different requirements of an environment for such a visual language may be addressed using Fujaba graph transformations. This covers abstract and concrete syntax, static and operational semantics, and model transformations. This case study shows, how the more sophisticated language elements of Fujaba may be exploited in modeling complex aspects of the statechart environment. In addition, we address some not graph grammar related aspects in building such an environment, e.g. the graphical user interface and multi-user support.     

Meta-modelling and graph grammars for multi-paradigm modelling in AToM<Superscript>3</Superscript>

This paper presents the combined use of meta-modelling and graph grammars for the generation of visual modelling tools for simulation formalisms. In meta-modelling, formalisms are described at a meta-level. This information is used by a meta-model processor to generate modelling tools for the described formalisms. We combine meta-modelling with graph grammars to extend the model manipulation capabilities of the generated modelling tools: edit, simulate, transform into another formalism, optimize and generate code. We store all (meta-)models as graphs, and thus, express model manipulations as graph grammars.We present the design and implementation of these concepts in AToM³ (A_To_ol for M_ulti-formalism, M_eta-M_odelling). AToM³ supports modelling of complex systems using different formalisms, all meta-modelled in their own right. Models in different formalisms may be transformed into a single common formalism for further processing. These transformations are specified by graph grammars. Mosterman and Vangheluwe [18] introduced the term multi-paradigm modelling to denote the combination of multiple formalisms, multiple abstraction levels, and meta-modelling. As an example of multi-paradigm modelling we present a meta-model for the Object-Oriented Continuous Simulation Language OOCSMP, in which we combine ideas from UML class diagrams (to express the OOCSMP model structure), Causal Block Diagrams (CBDs), and Statecharts (to specify the methods of the OOCSMP classes). A graph grammar is able to generate OOCSMP code, and then a compiler for this language (C-OOL) generates Java applets for the simulation execution.     

Defining the abstract syntax of visual languages with advanced graph grammars—A case study based on behavior trees

Diagrammatic visual languages can increase the ability of engineers to model and understand complex systems. However, to effectively use visual models, the syntax and semantics of these languages should be defined precisely. Since most diagrammatic visual models that are currently used to specify systems can be described as (directed) typed graphs, graph grammars have been identified as a suitable formalism to describe the abstract syntax of visual modeling languages. In this article, we investigate how advanced graph-transformation techniques, such as conditional, structure-generic and type-generic graph-transformation rules, can help to improve and simplify the specification of the abstract syntax of a visual modeling language. To demonstrate the practicability of an approach that unifies these advanced graph-transformation techniques, we define the abstract syntax of behavior trees (BTs), a graphical specification language for functional requirements. Additionally, we provide a translational semantics of BTs by formalizing a translation scheme to the input language of the SAL model checking tool for each of the graph-transformation rules.     

上下文相关图文法分析及其应用初探

图文法是一种对可视化语言进行形式化定义的元语言，具有表达自然、能力强大的特点.随着使用可视化语言的最终用户编程技术的广泛应用，图文法分析尤其是上下文相关图文法分析在工程应用中的重要性日益突出.国内外相关文献或着重于纯理论探讨，或局限于特定语法类的特定应用，不利于工程应用人员参考.本文选取简洁明了的符号体系，介绍上下文相关图文法分析的一般性过程，并将其中规则选取关键步骤描述为CSP问题，利用已有的针对CSP问题的优化方法来优化算法，介绍了现有的优化方法并给出实现算法;同时，结合自身实践，讨论其在一个面向体系结构的Web服务集成系统中的应用.     

Using Meta-Modelling and Graph Grammars to Create Modelling Environments

This paper presents the combined use of meta-modelling and graph grammars for the generation of visual modelling tools for simulation formalisms. In meta-modelling, formalisms are described at a meta-level. This information is used by a meta-model processor to generate modelling tools for the described formalisms. We combine meta-modelling with graph grammars to extend the model manipulation capabilities of the generated modelling tools, as we store (meta-)models as graphs, and thus, express model manipulations as graph grammars.We show the design and implementation of these concepts in AToM³ (A Tool for Multi-formalism, Meta-Modelling). As an example we will present a meta-model for Causal Block Diagrams and a graph grammar to generate OOCSMP code, a continuous simulation language which has a compiler able to generate Java applets from the simulations models.     

Techniques for Edge Stratification of Complex Graph Drawings

We propose an approach that allows a user (e.g., an analyst) to explore a layout produced by any graph drawing algorithm, in order to reduce the visual complexity and clarify its presentation. Our approach is based on stratifying the drawing into layers with desired properties; to this aim, heuristics are presented. The produced layers can be explored and combined by the user to gradually acquire details. We present a user study to test the effectiveness of our approach. Furthermore, we performed an experimental analysis on popular force-directed graph drawing algorithms, in order to evaluate what is the algorithm that produces the smallest number of layers and if there is any correlation between the number of crossings and the number of layers of a graph layout. The proposed approach is useful to explore graph layouts, as confirmed by the presented user study. Furthermore, interesting considerations arise from the experimental evaluation, in particular, our results suggest that the number of layers of a graph layout may represent a reliable measure of its visual complexity. The algorithms presented in this paper can be effectively applied to graph layouts with a few hundreds of edges and vertices. For larger drawings that contain lots of crossings, the time complexity of our algorithms grows quadratically in the number of edges and more efficient techniques need to be devised. The proposed approach takes as input a layout produced by any graph drawing algorithm, therefore it can be applied in a variety of application domains. Several research directions can be explored to extend our framework and to devise new visualization paradigms to effectively present stratified drawings.     

Grammar-based model transformations: Definition,execution, and quality properties

Model transformation is a key concept in model-driven software engineering. The definition of model transformations is usually based on meta-models describing the abstract syntax of languages. While meta-models are thereby able to abstract from superfluous details of concrete syntax, they often loose structural information inherent in languages, like information on model elements always occurring together in particular shapes. As a consequence, model transformations cannot naturally re-use language structures, thus leading to unnecessary complexity in their development as well as in quality assurance.In this paper, we propose a new approach to model transformation development which allows to simplify the developed transformations and improve their quality via the exploitation of the languages׳ structures. The approach is based on context-free graph grammars and transformations defined by pairing productions of source and target grammars. We show that such transformations have important properties: they terminate and are sound, complete, and deterministic.     

Synchronization of abstract and concrete syntax in domain-specific modeling languages

Modern domain-specific modeling (DSM) frameworks provide refined techniques for developing new languages based on the clear separation of conceptual elements of the language (called abstract syntax) and their graphical visual representation (called concrete syntax). This separation is usually achieved by recording traceability information between the abstract and concrete syntax using mapping models. However, state-of-the-art DSM frameworks impose severe restrictions on traceability links between elements of the abstract syntax and the concrete syntax. In the current paper, we propose a mapping model which allows to define arbitrarily complex mappings between elements of the abstract and concrete syntax. Moreover, we demonstrate how live model transformations can complement mapping models in providing bidirectional synchronization and implicit traceability between models of the abstract and the concrete syntax. In addition, we introduce a novel architecture for DSM environments which enables these concepts, and provide an overview of the tool support.     

Augmenting Node-Link Diagrams with Topographic Attribute Maps

We propose a novel visualization technique for graphs that are attributed with scalar data. In many scenarios, these attributes (e.g., birth date in a family network) provide ambient context information for the graph structure, whose consideration is important for different visual graph analysis tasks. Graph attributes are usually conveyed using different visual representations (e.g., color, size, shape) or by reordering the graph structure according to the attribute domain (e.g., timelines). While visual encodings allow graphs to be arranged in a readable layout, assessing contextual information such as the relative similarities of attributes across the graph is often cumbersome. In contrast, attribute-based graph reordering serves the comparison task of attributes, but typically strongly impairs the readability of the structural information given by the graph's topology. In this work, we augment force-directed node-link diagrams with a continuous ambient representation of the attribute context. This way, we provide a consistent overview of the graph's topological structure as well as its attributes, supporting a wide range of graph-related analysis tasks. We resort to an intuitive height field metaphor, illustrated by a topographic map rendering using contour lines and suitable color maps. Contour lines visually connect nodes of similar attribute values, and depict their relative arrangement within the global context. Moreover, our contextual representation supports visualizing attribute value ranges associated with graph nodes (e.g., lifespans in a family network) as trajectories routed through this height field. We discuss how user interaction with both the structural and the contextual information fosters exploratory graph analysis tasks. The effectiveness and versatility of our technique is confirmed in a user study and case studies from various application domains.     

Multimedia layout adaptation through grammatical specifications

Online multimedia presentations, such as news, need to be constantly updated. Increasing demands are also being made for accessing online multimedia documents from mobile devices such as PDAs. There is an urgent need for a sound but practical formalism that supports automatic adaptation to the change of media content, display environments, and user intention. This paper presents a visual language approach to the layout adaptation of multimedia objects. The underlying theory of our approach is a context-sensitive graph grammar formalism enriched with facilities for spatial representation and specification. The paper focuses on the issues and techniques for size adaptation and style adaptation in response to the change of device requirements and user interactions.Published online: 2 February 2005 Correspondence to: Kang Zhang     

Tool Modeling with Fujaba

This paper is a small tutorial on tool building with Fujaba. With the help of a small case study, we exemplify how the different requirements of an environment for a visual language may be addressed using Fujaba graph transformations. This covers abstract and concrete syntax, static and operational semantics, and model transformations. This case study shows, how the more sophisticated language elements of Fujaba may be exploited in modeling complex aspects of the desired CASE tool. In addition, we address some not graph grammar related aspects in building such an environment, e.g. the graphical user interface and multi-user support.     

Graph grammars with string-regulated rewriting

Multicellular organisms undergo a complex developmental process, orchestrated by the genetic information in their cells, in order to form a newborn individual from a fertilized egg. This complex process, not completely understood yet, is believed to have a key role in generating the impressive biotic diversity of organisms found on earth. Inspired by mechanisms of Eukaryotic genetic expression, we propose and analyse graph grammars with string-regulated rewriting. In these grammatical systems a genome sequence is represented by a regulatory string, a graph corresponds to an organism, and a set of graph grammar rules represents different forms of implementing cell division. Accordingly, a graph derivation by the graph grammar resembles the developmental process of an organism. We give examples of the concept and compare its generative power to the power of the traditional context-free graph grammars. We demonstrate that the power of expression increases when genetic regulation is included in the model, as compared to non-regulated grammars. Additionally, we propose a hierarchy of string-regulated graph grammars, arranged by expressive power. These results highlight the key role that the transmission of regulatory information during development has in the emergence of biological diversity.     

vCGG:一种基于虚结点的空间图文法形式框架

作为一种二维的形式化方法,图文法为可视化语言提供了直观而规范的描述手段.然而,大多数图文法形式框架在空间语义处理能力方面有所不足,影响了图文法的表达能力及其实际应用范围.针对现存的问题,构建了一种新型空间图文法形式框架vCGG （virtual-node based coordinate graph grammar）.区别于其他空间图文法,vCGG在产生式中通过定义虚结点的概念描述产生式与主图之间的语法结构与空间语义关系,在保留抽象能力的同时,提高了其空间语义配置性能.通过与几种典型空间图文法框架比较,vCGG形式框架在直观性、规范性、表达能力以及分析效率方面均有着较好的表现.     

Distributed Event Graphs: Formalizing Component-based Modelling and Simulation

In this work an extension to the classical Event Graphs formalism for discrete-event simulation is presented. The extensions are oriented towards the specification of component-based models. The abstract syntax has been defined through meta-modelling. Several methodological issues are discussed, concerning the use of two different meta-modelling levels or collapsing the language into a single one, where “instance-of” relationships are used between processes and their classes. The operational semantics have been defined through graph transformation. This formal definition enables analysis before code is generated from the model. The syntax and semantics of the visual language have been implemented in the multi-paradigm tool AToM³, together with a code generator that produces stand-alone applications able to run the analysed models in real-time.     

Parsing nonlinear languages

The diagrammatic approach to user interfaces for computer-aided software development toolkits, visual query systems, and visual programming environments, is based on the use of diagrams and charts traditionally drawn on paper. In particular, the VLG system (Visual Language Generator) has been proposed to generate icon-oriented visual languages customized for given applications. The syntactical model underlying the interpretation of a visual language in VLG has been designed to describe icon-oriented visual languages. In order to enable the VLG system to apply to any kind of graphical languages, like diagrammatic ones, it is necessary to find a more general syntactical model able to support both their generation and interpretation. This paper addresses the comprehension of the features that a grammatical formalism for nonlinear languages must have to match any requirement for an efficient parsing. To this aim, relation grammars support an easy implementation of a general parsing algorithm for multidimensional languages, parametric with respect to the rewriting rules of the grammar. We compare the expressive power of relation grammars to grammatical formalisms for graph grammars     

Parsing and translation of (attributed) expansive graph languages for scene analysis

In this paper, we suggest a class of (attributed) expansive graph grammars which generate languages contained in a graph family ?. It turns out that by means of node renumbering using a very effi-cient algorithm, any graph in ? can be converted into a standard form, which enables the use of related string representation for that graph to facilitate the syntax analysis. As a consequence, the syntax analysis of (attributed) expansive graph language is very efficient and almost like the parsing of tree languages. Furthermore, a syntax-directed transla-tion can be established for mapping one (attributed) expansive graph language to another. Finally, since many relational graphs for scene analysis can be considered as belonging to these graph languages, the proposed graph grammar model appears to be quite attractive from the application point of view.     

上下文相关图文法的表达能力分析

上下文相关图文法是描述可视化语言的形式化工具.为了直观地刻画并高效地分析可视化语言,已有图文法形式框架均着重于文法形式和分析算法的研究,而忽略了对它们之间表达能力的分析.在对已有上下文相关图文法形式框架的关键特征进行分析和归纳的基础上,通过构造不同形式框架之间的转换算法,揭示并形式化证明了它们表达能力之间的关系.而且,转换算法在不同形式框架之间建立了关联,使图文法的应用不必再局限于一个框架,而是可以选择不同框架分别进行图的描述和分析,从而提高了上下文相关图文法的易用性.     

Graph transformations and software engineering: Success stories and lost chances

Textual as well as visual and diagrammatic notations are essential in software engineering, and are used in many different contexts. Chomsky grammars are the key tool to handle textual notations, and find many applications for textual languages. Visual and diagrammatic languages add spatial dimensions that reduce the applicability of textual grammars and call for new tools.Graph transformation systems have been studied for over 40 years and are a powerful tool to deal with syntax, semantics and transformation of diagrammatic notations. The enormous importance of visual and diagrammatic languages and the strong support that graph transformation provide to the manipulation of diagrammatic notations would suggest a big success of graph transformation in software engineering.Graph transformation systems find their application both as language generating devices and specification means for system evolution, and thus can have many applications in software engineering. In this paper we discuss the main features of graph transformation and how they can help software engineers. We look back to the many attempts to use graph transformations in software engineering in the last 15 years, identify some success stories, and discuss to what extent graph transformation succeeded, when they have not succeeded yet, what are the main causes of failures, and how they can help software engineering in the next 15 years.     

Graph rewriting systems for the entity-relationship approach

Sequential graph rewriting systems are proposed as a meta-level formalism providing the concise and sound definition of different ER diagram languages. These rewriting systems can be used to define ER-based approaches for various DB modelling subtasks like schema design, evolution and integration. In addition, they are a natural choice for syntax directed ER CASE workbenches. In particular, by using specialized ER graph rewriting systems as meta input for CASE tools, the resulting tool behavior can be guided and controlled. Moreover, grammar driven modelling tools can be easily adapted for the needs of a particular enterprise or software factory without superimposing a particular ER dialect on the end users. Additional benefits result from the use of ER graph rewriting systems as a comparison framework for the continuously enlarging set of ER dialects.

The presentation includes material on the ER graph rewriting formalism, i.e., the actual tool, as well as an introduction to some formal graph rewriting prerequisites. An exemplary application, in particular ER graph generation, is used to clarify the underlying formal concepts.     

Visual coding by optimal graph-coloring

A formal study of visual codings in user interface design is presented. Visual codings for maximum distinction of different objects in displayed images are formulated as a discrete optimization problem of maximum-distance graph-coloring. The formulation is a generalization of the classical coloring problem in graph theory. Having pointed out that maximum-distance graph-coloring is NP-complete, we develop new, fast approximation algorithms for optimal visual codings. The proposed algorthms run inO (M N) time, whereM is the number of visual codes used andN is the number of objects to be encoded. Besides being efficient, the algorithms are simple and easy to implement. Our experiments showed that geographic maps automatically colored by the new algorithms were preferred to those colored by the previous graph-theoretical approach and they are competitive, if not better, in terms of the visual distinction of different regions than those drawn by hand.Supported by grans from Natural Science and Enginneering Research Council of Canada