OMT-G Designer is an online diagramming application for the design of geographic database systems and applications based on OMT-G, an object-oriented data model for geographic applications. It aims to increase the practical and academic uses of this data model, by providing an open and platform-independent modeling resource. 
The tool provides various consistency checks on the integrity of the schema, and includes a function that maps OMT-G geographic conceptual schemas into physical schemas of PostgreSQL/PostGIS and Oracle Spatial, including the necessary spatial integrity constraints.
OMT-G Designer is currently running under the link: http://www.aqui.io/omtg/
The OMT-G (Object Modeling Technique for Geographic Applications) is an object oriented data model for the design of geographic applications and geographic database systems. It provides primitives for modeling the geometric shape and location of geographic objects, supporting spatial and topological relationships, "whole-part" structures, networks, and multiple representations of objects and spatial relationships. The OMT-G data model reduces the distance between the conceptual project and the physical implementation of geographic applications, by allowing a more precise definition of the required objects, operations and visualization parameters. 
License and Copyright
OMT-G Designer is released under a MIT license.
Copyright (c) 2013 Luís Eduardo Oliveira Lizardo.
 K. A. V. Borges, C. A. Davis Jr., and A. H. F. Laender. OMT-G: an object-oriented data model for geographic applications. GeoInformatica, 5(3):221–260, 2001.
 L. E. O. Lizardo and C. A. Davis Jr. OMT-G Designer: a web tool for modeling geographic databases in OMT-G. In Advances in Conceptual Modeling: 33rd International Conference on ConceptualModeling, ER 2014, volume 8823 of Lecture Notes in Computer Science, pages 228–233. Springer International Publishing, 2014.