Steffen Mazanek

Business Process Models as a Showcase for Syntax-Based Assistance in Diagram Editors

Recently, a generic approach for syntax-based user assistance in diagram editors has been proposed that requires the syntax of the visual language to be defined by a graph grammar. The present paper describes how this approach can be applied to the language of business process models (BPMs), which is widely used nowadays. The resulting BPM editor provides the following assistance features: combination or completion of BPM fragments, generation of BPM examples, an extensive set of correctness-preserving editing operations for BPMs, and auto-link, i.e., the automatic connection of activities by sequence flow. Furthermore, this paper contains a discussion of the scalability and scope of the used approach. This also comprises a characterization of the languages where it can be put to a good use.

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.

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.

Sketch-based Diagram Editors with User Assistance based on Graph Transformation and Graph Drawing Techniques

In the last years, tools have emerged that recognize sketched diagrams of a particular visual language. That way, the user can draw diagrams with a pen in a natural way and still has available most processing capabilities. But also in the domain of conventional diagram editors, considerable improvements have been achieved. Among other features, powerful user assistance like auto-completion has been developed, which guides the user in the construction of correct diagrams. The combination of these two developments, sketching and guidance, is the main contribution of this paper. It not only shows feasibility and usefulness of the integration of user assistance into sketching editors, but also that novel user strategies for identifying and dealing with recognition errors are made possible that way. The proposed approach heavily exploits graph transformation and drawing techniques. It was integrated into a meta-tool, which has been used to generate an editor for business process models that comprises the features described in this paper.

Functional-Logic Graph Parser Combinators

Parser combinators are a popular technique among functional programmers for writing parsers. They allow the definition of parsers for string languages in a manner quite similar to BNF rules. In recent papers we have shown that the combinator approach is also beneficial for graph parsing. However, we have noted as well that certain graph languages are difficult to describe in a purely functional way. In this paper we demonstrate that functional-logic languages can be used to conveniently implement graph parsers. Therefore, we provide a direct mapping from hyperedge replacement grammars to graph parsers. As in the string setting, our combinators closely reflect the building blocks of this grammar formalism. Finally, we show by example that our framework is strictly more powerful than hyperedge replacement grammars. We make heavy use of key features of both the functional and the logic programming approach: Higher-order functions allow the treatment of parsers as first class citizens. Non-determinism and logical variables are beneficial for dealing with errors and incomplete information. Parsers can even be applied backwards and thus be used as generators or for graph completion.

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.

On the importance of model comparison tools for the automatic evaluation of the correctness of model transformations

The transformation judge is a novel system for the automatic evaluation and comparison of model transformations that have been submitted as solutions for common model transformation tasks. Its most important feature is the correctness check that is done by black-box-testing. This paper discusses why model comparison tools are crucial for the judge and which of their features are most important in this scenario. We also describe how a first model comparison tool has been integrated into our system and how the judge could be used to compare comparison tools.

Tool demonstration of the transformation judge

The transformation judge is a novel system for the automatic evaluation and comparison of graph and model transformations that have been submitted as solutions for common transformation tasks such as those accepted as case studies for the transformation tool contest. The most important feature of this system is the correctness check that is done by black-box-testing. But also performance data and other information about the solutions are collected. So, for academic as well as industrial users of transformation tools, the judge could be a good starting point for choosing a particular transformation tool for their respective task, since they can easily explore and compare different solutions for similar tasks. In this demonstration we show the most important use cases of the judge, i.e., uploading of cases and corresponding solutions as well as the automatic evaluation and comparison of solutions.

Visual Specification of Layout

We give an overview of a drawing approach that combines the concepts constraint satisfaction, attribute evaluation and transformation. The approach is tailored to an editor for visual languages, which supports structured editing as well as free-hand editing. In this paper, we focus on the visual specification of such a layout algorithm. As a running example, deterministic finite automata are used.

Graph Parser Combinators

A graph language can be described by a graph grammar in a manner similar to a string grammar known from the theory of formal languages. Unfortunately, graph parsing is known to be computationally expensive in general. There are quite simple graph languages that crush most general-purpose graph parsers. In this paper we present graph parser combinators, a new approach to graph parsing inspired by the well-known string parser combinators. The basic idea is to define primitive graph parsers for elementary graph components and a set of combinators for the construction of more advanced graph parsers. Using graph parser combinators special-purpose graph parsers can be composed conveniently. Thereby, language-specific performance optimizations can be incorporated in a flexible manner.