Chapter 1-5, 7 Summary Flashcards
(25 cards)
Relationships
interaction between entities
Database
organized collection of logically related data
Strong Entity
exists independently of other entities
Weak Entity
exists only because of another entity
Composite Attribute
can be broken down in several parts
{ }
multi-valued attribute
[ ]
derived attribute
Identifier
uniquely identifies the entity instance
Associative Entity
~many to many
~the resulting associative entity
has a meaning and could have its
own identifier
~ the resulting associative entity is in another relationship
~the resulting associative entity has 1 or more attributes
Subtype
subgrouping of the entities of an entity type that is meaningful to the org.
instance of a supertype that’s a member of 2 subtypes or more?
overlap rule
instance of a supertype that isn’t member of 2 subtypes or more?
disjoint rule
Relation is represented as
2 dimensional table of data
Primary key
an attribute (or combination of attributes) that uniquely defines each row in the relation
Composite key
Primary key made up of more than 1 attribute
Foreign key
relationship between 2 tables. Also is an attribute of a relation that serves as a primary key in another relation.
primary key must be
unique and non-null.
foreign key must
match a primary key value or must be null.
1NF
no multi-valued attributes in the relation
2NF
no partial functional dependency
3NF
no transitive functional dependency
Functional dependency
if a ==> b, then b is functionally dependent on a attributes of a relation
determinant
the attributes on the left side of a functional depedency
Candidate keys
Whatever isn’t being pointed to (==>)
