ERD Symbols and Meanings

This example was designed on the base of Wikimedia Commons file: Example ERD2.png.
"example entity relationship diagram showing relationship between lecturers and students" [commons.wikimedia.org/ wiki/ File:Example_ ERD2.png]
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. [creativecommons.org/ licenses/ by-sa/ 3.0/ deed.en]
"Relationship diagrams (also known as logical data models) are used to design relational databases and can be a good way of understanding the structures in a data set. The 3 building blocks of an Entity Relationship model are entities, attributes and relationships. An entity is a discrete and recognisable 'thing', either a pysical object ..., or concept ... Each entity can be physically represented as a table, where each column of the table is an attribute of the entity ... A relationship is a verb that links two or more entities. ... Importantly, relationships also have a cardinality that can be 'one to one', 'many to one', 'one to many' or 'many to many'. ... Many to many relationships are often a sign that a design needs to be further elaborated. For example the 'teaches' relationship between teachers and students at a university would be many to many and would require the introduction of entities like class and date to fully understand the relationship." [en.wikibooks.org/ wiki/ Data_ Science:_ An_ Introduction/ Thinking_ Like_ a_ Data_ Engineer]
The entity-relationship diagram example "Lecturers-students relationship ERD" was drawn using ConceptDraw PRO software extended with the Entity-Relationship Diagram (ERD) solution from the Software Development area of ConceptDraw Solution Park.