Modeling: Map real-world entities and relationships into a database (a scaled-down version of the real world with pieces we care about)

Entity/Relationship Model: A diagram-based data model

Schema: Structure for entities & relationships

• Entity Set: Category of objects (e.g. professors, courses)
• Relationship Set: Interactions between tables (e.g. professors teach courses)
• Attributes: Properties of entities or relationships
• Keys: Filled circle for single-attr key, a connected line with circles for multi-attr key.
• Foreign Key: Keys accross relationships Weak Entity Set: An entity set that doesn’t have a key among its attrs.
• Relationship-set Key: Combined key from entities that uniquely identifies a rel~

Instance: Specific entries following a schema

• Entity: A tuple. (e.g. Prof. Mario)
• Relationship: Link between ≥2 entity sets. (e.g. Prof. Mario teaches CSC258)

Recursive Relationship: Link between an entity to itself. (e.g. employee - <colleague> - employee)

Ternary Relationship: Link between 3 entities

Cardinality & Multiplicity

Relationship Cardinality: (min, max) specifies how many target entities can be in a R~ (e.g. employee - (1, 5) - <assign> - (0, 50) - task: an employee can be assigned 1-5 tasks, a task can have 0-50 employees assigned)

• Intuition: it's the # of lines from each entity connecting outward through the relationship
• Minimum Cardinality: If min = 0, optional participation (e.g. a task can have no employees assigned) If min = 1, mandatory participation (e.g. an employee must be assigned a task)
• A foreign key must come from a relationship where the participating entity is (1,1)