Sonja Maier

Auto-completion for diagram editors based on graph grammars

Graphs are known to be well-suited as an intermediate data structure in diagram editors. The syntax of a particular visual language can be defined by means of a graph grammar. In recent work we have proposed approaches to graph completion: given a possibly ldquoincompleterdquo graph, this graph is modified in such a way that the resulting graph is a member of the grammarpsilas language. In this paper we describe how graph completion can be used to realize diagram completion, an important requirement for the realization of content assist in diagram editors. With our approach, the advantages of free-hand and structured editing can be effectively combined: drawing of diagrams with maximal freedom and powerful guidance whenever needed.

A Generic Layout Algorithm for Meta-model Based Editors

The diagram editor generator framework DiaMeta utilizes meta-model based language specifications and supports free-hand as well as structured editing. This paper describes a generic layout algorithm that meets the demands of this kind of editors. The underlying concept of the algorithm is attribute evaluation. An attribute evaluator is best suited for an unambiguous layout, i.e. the diagram may not be represented in different ways. Especially in free-hand mode we want to give more freedom to the user when he edits a diagram, and thus a plain attribute evaluator is not sufficient. Therefore we combine this approach with a constraint satisfaction approach in the sense that constraints are used to activate particular attribute evaluation rules. This gives the layouter the flexibility it needs to deal with the situation in DiaMeta .

A Pattern-Based Layout Algorithm for Diagram Editors

The diagram editor generator framework DIAMETA utilizes meta-model-based language specifications and supports free-hand as well as structured editing. We presented a generic layout algorithm that meets the demands of this kind of editors. The algorithm combines two concepts, constraint satisfaction and attribute evaluation, to a powerful methodology for specifying the layout for a particular visual language. As the layout specification for this algorithm is rather complex, we encapsulated basic functionality into reusable patterns. This paper describes this pattern concept of the generic layout algorithm, and shows how they simplify the layout specification of a specific language.

An Algorithm for Hypergraph Completion According to Hyperedge Replacement Grammars

The algorithm of Cocke, Younger, and Kasami is a dynamic programming technique well-known from string parsing. It has been adopted to hypergraphs successfully by Lautemann. Therewith, many practically relevant hypergraph languages generated by hyperedge replacement can be parsed in an acceptable time. In this paper we extend this algorithm by hypergraph completion: If necessary, appropriate fresh hyperedges are inserted in order to construct a derivation. The resulting algorithm is reasonably efficient and can be directly used, among other things, for auto-completion in the context of diagram editors.

Pattern-Based Layout Specifications for Visual Language Editors

When creating an editor for a visual language, a challenging task is the layout specification. Many visual languages, e.g., Ecore diagrams or Petri nets, show similar layout characteristics, and hence reuse of layout behavior should be enabled. For that purpose, we introduce the concept of layout patterns, which encapsulates certain layout behavior. With the approach, it is possible to combine different layout algorithms, e.g., standard graph drawing algorithms and constraint-based algorithms. In addition, rule-based layout algorithms may be used that are specifically tailored to the interactive nature of visual language editors.

Layout Specification on the Concrete and Abstract Syntax Level of a Diagram Language

A visual language consists of several visual component types, e.g. states or transitions in DFAs. Nowadays, the language itself is usually specified via a meta model. To make a diagram look nice, a layouter is required. This layouter may either operate on the concrete syntax level, i.e., on the visual components, or on the abstract syntax level, i.e., on the model instance. In this paper we present an approach that is capable of specifying a flexible layout on both, the concrete as well as the abstract syntax level of a diagram. The approach uses pattern-based transformations. Besides structured editing, it also supports free-hand editing, a challenging task for the layouter. We introduce how such a specification can be created and examine the advantages and shortcomings of each of either operating on the concrete syntax level or on the abstract syntax level.

Recording, processing, and visualizing changes in diagrams

In this paper, we present methods and techniques to record, process, and visualize diagram changes. These methods help us understand diagram changes, and are the basis for more enhanced functionality, such as a more powerful undo functionality, or merging of different versions of a diagram. Our approach is based on the idea to record all diagram changes, including changes of the diagram layout. One of the main challenges is to provide a concise and comprehensible visualization of these changes. In order to produce such a visualization, the recordings need to be processed, comprising filtering and aggregation of changes. Our model-based approach is generic and makes use of the abstract and the concrete syntax (meaning and representation) of the specific diagram language.

Interactive diagram layout

We examine an approach for defining layout algorithms for diagrams. Such an algorithm is specified on an abstract level and may be applied to many kinds of visual languages. It mainly allows for incremental diagram drawing and attaches great importance on mental map preservation. With the approach, it is possible to combine graph drawing algorithms and other layout algorithms. It is capable of defining layout behavior for non-graph-like visual languages like Nassi-Shneiderman diagrams or GUI forms as well as graph-like visual languages such as class diagrams, mindmaps, or business process models. In this paper, we demonstrate that the combination of graph drawing algorithms and other layout algorithms is meaningful by presenting three visual language editors that have been created by students.

A Static Layout Algorithm for DiaMeta

The diagram editor generator framework DiaMeta utilizes meta-model-based language specifications and supports free-hand as well as structured editing. In this paper we present a layouting approach that is especially well suited for a static layout. It is based on the layout algorithm presented in a previous paper that uses the two concepts constraint satisfaction and attribute evaluation. This algorithm is combined with graph transformations and the result is a natural way of describing the layout of visual languages. As an example we use a simplified version of Sugiyamas algorithm, applied to statechart diagrams.

A Pattern-based Approach for Initial Diagram Layout

In a diagram editor, one can distinguish initial from incremental diagram layout. The former computes a diagram layout from scratch, whereas the latter adjusts an existing layout after diagram modifications. In previous work, we have proposed a pattern-based approach as a solution for incremental diagram layout in visual language editors. Each LP encapsulates certain layout behavior. A diagrams layout is then defined by simultaneously applying several LPs to the diagram. This solution has been designed for an interactive environment where the user may select and alter the layout behavior at runtime. This paper describes an extension of this approach that now supports initial diagram layout, too. While the old version only enabled freehand editing, the extended version now supports diagram import and structured editing as well.