Clustered graphs are graphs with recursive clustering structures over the vertices. This type of structure appears in many systems. Examples include CASE tools, management information systems, VLSI design tools, and reverse engineering systems. Existing layout algorithms represent the clustering structure as recursively nested regions in the plane. However, as the structure becomes more and more complex, two dimensional plane representations tend to be insufficient. In this paper, firstly, we describe some two dimensional plane drawing algorithms for clustered graphs; then we show how to extend two dimensional plane drawings to three dimensional multilevel drawings. We consider two conventions: straight-line convex drawings and orthogonal rectangular drawings; and we show some examples. 1 Introduction Graph drawing algorithms are widely used in graphical user interfaces of software systems. As the amount of information that we want to visualize becomes larger, we need more structure ...

A graph drawing algorithm produces a layout of a graph in two- or three-dimensional space that should be readable and easy to understand. Since the aesthetic criteria differ from one application area to another, it is unlikely that a definition of the "optimal drawing" of a graph in a strict mathematical sense exists. A large number of graph drawing algorithms taking different aesthetic criteria into account have already been proposed. In this paper we describe the design and implementation of the AGD--Library, a library of Algorithms for Graph Drawing. The library offers a broad range of existing algorithms for two-dimensional graph drawing and tools for implementing new algorithms. The library is written in C++ using the LEDA platform for combinatorial and geometric computing ([16, 17]). The algorithms are implemented independently of the underlying visualization or graphics system by using a generic layout interface. Most graph drawing algorithms place a set of restriction...

Graphs are commonly used to model relations in computer systems. Nodes are used to represent entities in an application, and edges represent relationships between entities. Many graph based applications need to provide user interfaces for the user to create and edit graphs depicted as diagrams. The underlying graph model should be powerful enough to represent a wide range of applications yet simple enough to enable good layout. In this paper we propose a new model: cigraphs. In a cigraph, each node may consist of a (sub)cigraph. Layout functions are assigned to nodes (that is, to sub-cigraphs) in an object-oriented fashion; this allows considerable user control of layout. Keywords: graph, graph drawing, formalism, cigraph, user interface. 1 Introduction Diagrams of graphs have been widely used in human-computer interaction. A graph is a set of nodes and edges. Graphs are commonly used to model relations in computer systems. Nodes are used to represent entities in an application, and...

. Graphlet is a portable toolkit for graph editors and graph drawing algorithms, and is the successor of the GraphEd system. Graphlet is based on LEDA and Tcl/Tk. It provides interfaces for C++ and LedaScript, a high level scripting language. A large number of graph editor and graph layout systems have been developed in recent years ([8, 2, 1]). The scope of these systems ranges from small and onpurpose systems to large, complex ones. However, the programming interfaces and file formats of most of these systems are mutually incompatible. Graphlet is a portable toolkit for implementing graph editors and graph drawing algorithms with a modular, extensible design. Graphlet is the successor of GraphEd [5]. Unlike its predecessor, it is portable and uses three external toolkits (LEDA, Tcl and Tk). It provides a C++ programming interface, a scripting language and a new, portable file format. LEDA [6] is a library of efficient data structures and algorithms. It is the implementation base for...