ABSTRACT. We are developing a rule-based implementation of a tool to analyse and generate graphs. It is used in the domain of mason's marks. For thousands of years, stonemasons have been inscribing these symbolic signs on dressed stone. Geometrically, mason's marks are line drawings. They consist of a pattern of straight lines, sometimes circles and arcs. We represent mason's marks by connected planar graphs.

Our prototype tool for analysis and generation of graphs is implemented in the rule-based declarative language Constraint Handling Rules (CHR). It features

- a vertex-centric logical graph representation as constraints, - derivation of properties and statistics from graphs, - recognition of (sub)graphs and patterns in a graph, - automatic generation of graphs from given constrained subgraphs, - drawing graphs by visualization using svg graphics

In particular, we started to use the tool to classify and to invent mason's marks. In principe, our tool can be applied to any problem domain that admits a modeling as graphs. The drawing and generation module of our tool is available online at http://chr.informatik.uni-ulm.de/mason.