GXL (Graph eXchange Language) is designed to be a standard exchange format for graphs. GXL is an extensible markup language (XML) sublanguage and the syntax is given by an XML document type definition (DTD). This exchange format offers an adaptable and flexible means to support interoperability between graph-based tools. Overview In particular, GXL was developed to enable interoperability between software reengineering tools and components, such as code extractors (parsers), analyzers and visualizers. GXL allows software reengineers to combine single-purpose tools especially for parsing, source code extraction, architecture recovery, data flow analysis, pointer analysis, program slicing, query techniques, source code visualization, object recovery, restructuring, refactoring, remodularization, etc., into a single powerful reengineering workbench. There are two innovative features in GXL that make it well-suited to an exchange format for software data. The conceptual data model is a typed, attributed, directed graph. This is not to say that all software data ought to be manipulated as graphs, but rather that they can be exchanged as graphs. It can be used to represent instance data as well as schemas for describing the structure of the data. Moreover, the schema can be explicitly stated along with instance data. The structure of graphs exchanged by GXL streams is given by a schema represented as a Unified Modeling Language (UML) class diagram. Since GXL is a general graph exchange format, it can also be used to interchange any graph-based data, including models between computer-aided software engineering (CASE) tools, data between graph transformation systems, or graph visualization tools. GXL includes support for hypergraphs and hierarchical graphs, and can be extended to support other types of graphs. GXL originated in the merger of GRAph eXchange format (GraX: University of Koblenz, DE) for exchanging typed, attributed, ordered, directed graphs (TGraphs), Tuple Attribute Language (TA: University of Waterloo, CA), and the graph format of the PROGRES graph rewriting system (University Bw München, DE). Furthermore, GXL includes ideas from exchange formats from reverse engineering, including Relation Partition Algebra (RPA: Philips Research Eindhoven, NL) and Rigi Standard Format (RSF: University of Victoria, CA). The development of GXL was also influenced by various formats used in graph drawing (e.g. daVinci, Graph Modelling Language (GML), Graphlet, GraphXML) and current discussions on exchange formats for graph transformation systems. Presentations of former GXL versions At the 2000 International Conference on Software Engineering (ICSE 2000) Workshop on Standard Exchange Formats (WoSEF), GXL was accepted as working draft