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What do single line with an arrow mark in ER diagram represent?
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Entity Relationship Diagram Symbols & Notations mainly contains three basic symbols which are rectangle, oval and diamond to represent relationships between elements, entities and attributes. There are some sub-elements which are based on main elements in ERD Diagram.
You can see various combinations of ERD relation arrows below: 1 : 1 - one-to-one relationship - depicted as full circles on both sides.
Dotted lines for Relationships in a Logical Model indicate that the Relationship is optional (i.e. that an Entity does not need to participate in the Relationship). Similarly, a dotted line for a Foreign Key in a Relational Model indicates that the Foreign Key constraint is optional.
Total Participation − Each entity is involved in the relationship. Total participation is represented by double lines. Partial participation − Not all entities are involved in the relationship. Partial participation is represented by single lines.
As per Bachman Notation which you are using ,
"For every relation a rectangle has to be drawn and every coupling is illustrated by a line that connects the relations. On the edge of each line arrows indicate the cardinality. We have 1-to-n, 1-to-1 and n-to-m"
And "Cardinality use to represent the relationship between two entities."
For more on cardinality Notations
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E.R diagrams represent entities as boxes, and relationships as lines between the boxes. The ends of these lines are shaped to represent the cardinality of the relationship
an arrow from entity set to relationship set indicates a key constraint, i.e. injectivity: each entity of the entity set can participate in at most one relationship in the relationship set;
Have a look at these resources also for better understanding
example1
example2
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