Week 1 Flashcards
What are the three components of the design process?
Conceptual Design, Logical Design, Physical Design
What is conceptual design concerned with?
Providing a detailed overview of the enterprise and producing an ER model to illustrate entities, relationships, attributes and constraints on entities
What is logical design concerned with?
Mapping the high level conceptual scheme onto the implementation data model that will be used by the database system (relational data model)
What is physical design concerned with?
Specifying the physical features of a database, including file organization and choice of index structures
What is an entity/entity set?
An entity is a thing or object in the real world that is distinguishable from all other objects.
What is a derived attribute?
An attribute such that the value of that attribute can be derived from values of other related attributes or entities
What three main things are illustrated in an ER diagram?
Entity, Relationships, Attributes
What is an entity set?
An entity set is a collection of entities that share the same properties and attributes.
What is an attribute?
Descriptive properties possessed by each member of an entity set
What is a relationship?
Association among several entities
What is a relationship set?
Set of relationships (associations among several entities) of the same type
What are the two ways to participate in a relationship[?
Total or partial
What is a cardinality of a relationship set?
MAXIMUM number of times an entity can be associated with a relationship set
What are the three cardinalities of relationships?
One to one, One to Many, Many to One
Describe a one to many relationship
An entity in A is associated with any number of entities in B
Describe a many to one relationship
An entity in A is associated with at most one entity in B, however an entity in B can be associated with any number of entities in A
What does the set of candidate keys represent?
All the attributes that could be used to uniquely identify the entity
What is a superkey?
The union of all the primary keys of entities within a relationship set
What is the primary key of a relationship set?
Union of the primary keys of those participating entity sets that do not have an incoming arrow from the relationship set R
What is the participation of a relationship set?
Minimum number of times an entity can be associated with a relationship set
What is a weak entity set?
An entity set that doesn’t have sufficient attributes to be able to form a primary key, can’t be uniquely identified without referring to another relationship/entity set
What is aggregation?
The abstraction in which relationship sets are treated as higher level entity sets which can participate in relationships
What is a discriminator?
The identifying attributes in a weak entity sets that when paired with the identifying relationship/entity set can be used to uniquely identify entities in a weak entity set
