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One to many relationship is denoted by 1---*, but I can't figure out 0..1---*.
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The Entity Relationship Diagram ( ERD ) is a graphical representation of the database structure. The ERD is also alternately referred to as ER Model or ER Diagram. In simple words , the entity relationship diagram is a blueprint that can used to create a database using a specific database management system ( DBMS ).
Entity Relationship (ER) Model. The entity-relationship (ER) data model is created out of the activity of utilizing commercially accessible DBMS to model application database. Prior, business systems depended on the various leveled and network approach. The entity-relationship model is a speculation of these models.
The ER or (Entity Relational Model) is a high-level conceptual data model diagram. Entity-Relation model is based on the notion of real-world entities and the relationship betwee ER Diagram Tutorial in DBMS (with Example)
If you have a large diagram, consider using colours to highlight different sections, or breaking it up into smaller diagrams. Be consistent with your naming and the symbols you use. An Entity Relationship Diagram is a great tool to help you define, understand, and communicate the requirements of a system.
None or One.
Basically when you have have a foreign key column that can be null.
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