erd (hackage): erd transforms a plain text description of a relational database schema to a graphical representation of that schema. It is intended that the graph make use of common conventions when depicting entity-relationship diagrams, including modeling the cardinality of relationships between entities.  A quick example that transforms an er file to a PDF is just below. The original source file can be found amongst the examples in the repository.  The PDF should now contain a graph that looks like this:
Keywords: database|development|program|public-domain