All those database design terms might be confusing. In this short article I will try explain what they are and what the differences are.
Abstract model that organizes data elements and their relationships. It is not related to any implementation. Data model may be represented in many forms, such as Entity Relationship Diagram or UML Class Diagram.
Is a reference and description of each data element. It is a detailed definition and documentation of data model (learn more about data dictionary). It can have two levels of abstraction: physical and logical.
Database schema is a physical implementation of data model in a specific database management system. It includes all implementation details such as data types, constraints, foreign or primary keys.
Entity Relationship Diagram
ER diagrams are a graphical representation of data model/schema in relational databases. It is a modelling and a database documentation tool.
|Data Model||Database Schema||Data Dictionary (Logical)||Data Dictionary (Physical)||ERD|
|Stage||Conceptual system modeling||System implementation||Detailed system design, documentation||System implementation, documentation||Conceptual system modeling, documentation|
|Purpose||Data design||Database implementation||Define each data attribute in data model - data model supplement||Design and documentation of each data attribute in database schema||Communicate data model in relational databases|
|Level of detail||Low or medium - key objects/entities and attributes||High - every data and relation detail defined||High - every key table and data attribute defined||Very high - every table and column defined||Low or medium - key entities and attributes|
|Authors||Data/system architects, business analysts||Data/system architects, DBAs||Data/system architects, business analysts||Data/system architects, DBAs||Data architects, DBAs|
|Users||Business analysts, business users, data/system architects||Developers, DBAs||Business analysts, business users, data/system architects||Data/system architects, DBAs, developers, testers, system administrators||Business analysts, business users, data/system architects, DBAs, developers|
|Tools||CASE, diagramming tools||Database development & management tools||Word/Excel||Word/Excel, extended properties/comments, data dictionary tools||CASE, diagramming tools|
|Form||Graphical - UML Class Diagram, ERD||Structures in DBMS: tables, columns, foreign keys etc.||Tables of metadata||Tables of metadata||Diagram|