Entity Relationship Flashcards
Entity Type
Entities with the same basic attributes are grouped or typed together into the same entity type.
An entity type may have more than one key
Entity
A basic concept for the ER diagram.
Specific things or objects in the mini-world that are represented in the database.
an entity represents a concept or object that can be identified and described, such as a person, place, thing, or event.
Entities are depicted as rectangular boxes in ER diagrams, with the entity name written inside the box. Each entity has attributes that describe its properties, which are represented as ovals connected to the entity box by lines.
Attributes
Properties used to describe an entity. An attribute as a value set (data type) attributed to it.
an attribute is a characteristic or property that describes an entity. It is a piece of information that is associated with an entity and helps to define its identity.
Key Attribute
An attribute of an entity type for which each entity must have a unique value.
A key attribute may be composite.
Entity set
The current state of the entities of that type that are stored in the database.
Entity type
Entities with the same basic attributes are grouped or typed into the same entity type.
An entity type may have more than one key
Multi-valued Attribute
An entity may have different values for that attribute. Example: {Colour} or {PreviousDegree}
Simple attribute
Each entity has a single atomic value for the attribute.
Composite Attribute
The attribute may be composed of several components. Ex: adresse or full name
Derived Attribute
It’s value is dynamic and derived from another attribute. It is represented by dashed oval I’m an ER diagram. For example a person’s age is a derived attribute because its value changes over time
Recursive relationship type
A relationship between the same participating entity type in distinct time
Self-referencing relationship type
Same as recursive entity type
Weak entity type
An entity that did not have a key attribute and that is identification-dependent on another type
