- Why is the multivalue, multicolumn problem another form of the multivalued dependency problem?Both problems try to store multiple values on an attribute in a table. In the multivalue, multiplecolumn problem, the multiple values are stored in different columns. In the mutlivalued dependency problem the multiple values are stored in different rows. In both cases, the solution is the same: store the multiple values in a separate table.
- What is the inconsistent values problem? Include an example not used in the text.The inconsistent values problem occurs when different users or data sources use slightly different forms of the same data value. One example is where automobiles are specified as "Ford, 2-door, Red" in one cell and "Red Ford 2-door" in another.
- Explain the relationship between entity, entity class, and entity instance.An entity is something that can be identified in the users' work environment, something that the users want to track. Entities of a given type are grouped into entity classes. An entity instance is the representation of a particular entity.
- Explain the difference between attributes and identifiers.Entities have attributes. Attributes are properties that describe the entity's characteristics. Entity instances have identifiers. Identifiers are attributes that name, or identify, entity instances.
- Name and describe three types of binary relationships.
1:1 - a single entity instance of one type is related to a single-entity instance of another type.
1:N - a single entity instance of one type is related to many-entity instances of another type.
M:N - many-entity instances of one type relate to many-entity instances of another type.
- What is the archtetype/instance pattern?The archetype/instance pattern occurs when one entity tracks occurrences of another entity. A common example is the relationship between CLASS and SECTION, where the actual occurrence of a class happens when students register for a SECTION of that CLASS. The archetype/instance pattern is implemented as an ID-dependent relationship.