Database Design for Mere Mortals Ch. 12 Flashcards
Why can you refer to a view as a virtual table?
Because it draws data from base tables rather than storing data on its own
State two reasons why views are valuable.
— You can use them to work with data from multiple tables simultaneously
— They reflect the most current information contained in the base tables
— You can customize them to the specific needs of an individual or group of individuals
— You can use them to help enforce data integrity
— You can use them for security or confidentiality purposes
Name the types of views you can define as you design the logical structure of the database.
— Data
— Aggregate
— Validation
What does your RDMBS do each time you access a data view (or any type of view, for that matter)?
Your RDBMS will rebuild and repopulate it using the most current data from the view’s base tables
What determines the type of modifications you can make to a view’s data?
Field specifications and business rules determine the types of modifications you can make to a view’s data
What is the only requirement you must fulfill to define a multitable data view?
The tables you use to create the view must bear a relationship to each other
Why doesn’t a data view contain its own primary key?
Because it is not a table; a true table stores data and requires a primary key to serve as a unique identifier for each of its records
What is the purpose of an aggregate view?
To display information produced by aggregating a particular set of data in a specific manner
What are the most common aggregate functions that you can apply to a set of data?
Sum, average, minimum, maximum, and count
What is a grouping field?
A data field within an aggregate view that ‘groups’ multiple instances of a given value into a single instance of the value
True or False: You can modify the data in an aggregate view.
False
What is the difference between a validation table and a validation view?
The difference lies in their construction — a validation tables stores its own data, whereas a validation view draws data from its base tables
Name two points you would consider when identifying view requirements.
— Review your notes with the group
— Review the data entry, report, and presentation samples you gathered during the early stages of the design process
— Examine the tables and the subjects they represent
— Analyze the table relationships
— Study the business rules
When should you use calculated fields?
When they will provide pertinent and meaningful information or when they will enhance the manner in which the view uses its data
How do you define a view that displays only science-fiction books?
By applying a filter to the appropriate field within the view
