3. Entity-Relationship model Flashcards
database application
a particular database and the associated programs that implement the database queries and updates
Entity-Relationship (ER) model
high-level conceptual data model
ER diagrams
diagrammatic notation associated with the ER model
- requirements collection and analysis
understand data requirements and specify functional requirements
- conceptual design
Create conceptual schema using high-level conceptual data model
- functional analysis
identify high-level user operations
- logical design / data model mapping
conceptual schema transformed from high-level data model into implementation data model
- Physical design
internal storage structures, indexes, access paths and file organization for database files are specified
- application program design
and implemented as database transactions
entity
“thing” in the real world with an independent existence
attributes
properties that describe an entity
simple vs composite attribute
divisible in smaller subparts or not
single-valued vs multivalued attribute
single value or multiple values for one attribute
stored vs derived attribute
derivable from another attribute or not
null values
when attribute has no value (not applicable or unknown, missing/ unknown)
complex attributes
arbitrary nesting by grouping components between parentheses and separating by commas, multivalued between bracets
entity type
defines a collection of entities that have the same type
entity set
collection of all entities of a particular entity type in the database at any point in time
key attribute
attribute whose values are distinct for each individual entity in the set
value set (domain)
specified set of values that may be assigned to that attribute for each individual entity
relationships
references between entities
degree of a relationship type
number of participating entity types (binary if 2, ternary if 3)
role name
role that a participating entity from the entity type plays in each relationship instance
structural constraints
cardinality ratio and participation constraints
cardinality ratio
specifies max number of relationship instances that an entity can participate in
participation constraints (minimum cardinality constraint)
specifies whether the existence of an entity depends on its being related to another entity via the relationship type
total participation (existence dependency)
every entity in the set of an entity type must be related to a specific entity via a relationship
