Chapter 3 Flashcards
define entities
specific things or objects described by database
define attributes
properties used to describe an entity
what are the 2 types of attributes?
Simple = attribute has a single value composite = attribute composed of multiple attributes
what is a multi-valued attribute?
attribute that has multiple attributes
i.e a car can be red and black at the same time
define entity type
entities with the same basic attributes like a java class
define key attribute
attribute that distinguishes multiple entities of the same entity type
- Can be composite
define entity set
current state of all entities of an entity type
define value set
set of values associated with an attribute
define relationship
relates 2 or more distinct entities with a specific meaning
- degree of relationship is the number of participating entities
what are the 3 cardinality ratios?
specifies maximum participation
- 1 to 1
- 1 to many
- many to many
what are the 2 existence dependency constraints?
specifies minimum participation?
- zero (optional participation, existence-dependent)
- one or more (mandatory)
define weak entity type
entity that doesn’t have a key attribute and is dependent on another entity type for identification
define partial key
key attribute when combined another key attribute)
what are sub/super classes in enhanced ERDs?
- subclasses function just like java where subclasses inherit attributes of superclass (is a special case of a superclass)
- superclasses are general cases of subclasses, also like java
What are the 3 basic constraints of specializations
- Membership
- Disjointness
- Completeness
How can membership constraints be defined?
predicate/condition-defined: based on some condition
attribute defined: all subclasses have their membership condition on the same attribute
user defined: no condition so membership is specified by the user on an entity-to-entity basis
How can disjointness constraints be defined?
- entities of subclasses of the same superclass are mutually exclusive
- indicated by d
How can overlapping constraints be defined?
- entities of subclasses of the same superclass can overlap
- indicated by o
What is the total completeness constraint?
Every entity of the superclass must belong to some subclass indicated with double lines in eer
What is the partial completeness constraint?
an entity may not belong to any subclass indicated with single line in eer
