Oracle SQL Developer Data Modeling

Oracle SQL Developer Data Modeling is the latest product offering to join the Oracle Database Tools. SQL Developer Data Modeling offers a full spectrum of data and database modeling tools and utilities, including Entity Relationship modeling, Relational (Database Design), Data Type and Multidimensional modeling, full forward and reverse engineering and code generation. It includes importing from and exporting to a variety of sources and targets, provides a variety of formatting options and validates the models through a predefined set of Design Rules.

SQL Developer Data Modeling can connect to any Oracle Database version 9.2.0.1 and later, and is platform independent. Initially available as a standalone product, with future releases available as an extension to Oracle SQL Developer. The second Early Adopter release is stand alone and file-based only.

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Understanding Relationships in E-R Diagrams

Few articles about E-R diagrams worth to read:

Understanding Relationships in E-R Diagrams (part 1, 2, 3)
Documenting Entities, Attributes & Relationships
E-R Diagram Relationship Integrity Constraints
Interpreting Cardinality and Dependency on an E-R Diagram
Guidelines for Naming E-R Attributes
Recursion in E-R Relationships
Notations on Entity-Relationship Models
Entity-Relationship Diagram Checklist