Speaking in terms of graph properties, Entity-Relationship diagrams are undirected graphs.
We suggest to represent Entity-Relationship diagrams with orthogonal drawings, i.e., drawings in which the connections between symbols consist of horizontal and vertical segments only.
The following figures show examples of Entity-Relationship diagrams constructed with GDT.
GAPI tutorial on orthogonal drawings and BLAG tutorial on orthogonal drawings provide a comprehensive guide on how to use GDT to construct these widely used drawings.
An example of system that uses GDT for Entity-Relationship diagrams visualization is Information System Sculptor. Another related system is JBG.
Also, DBdraw is a very interesting tool for automatically visualizing a Microsoft Access database as a relational schema drawing.