Views

Question 1

Relational table

Answer 1

Description of a table, including a list of attributes together with any integrity constraints, primary and foreign key, etc…,

Question 2

Relational Variable

Answer 2

Actual table with data in it

It is a variable because if any data is added, removed or updated in it, its actual VALUE changes –> like a variable in any programming language

Question 3

Base Relational Variable

Answer 3

Relational variable that exists as some form of physical data, stored somehow

Question 4

Derived Relational Variable

Answer 4

Does not ever exist physically

Remains as a description (expression), evaluated when it is encountered in a program

TYPICALLY OBSERVED USING VIEWS -> views enable derived variables to exist temporarily, for certain purposes, without ever being stored for longer than is needed

User not necessarily aware that they are using a view, rather than a table –> has the same type as Base RV –> has the same closure properties as a table

Views are not evaluated, but stored in the catalog under a given name

Question 5

Understanding Views

Answer 5

Views are not evaluated, but are stored in the catalog under a given name

Alterations in the underlying data from which the View is built, are immediately reflected in the View

Alterations made to the data in the view are also reflected in the underlying data

Question 6

Reasons for using views

Answer 6

1) Concurrency: Lots of different users can view data in different ways –> can create views for different perspectives / different roles that people are in

2) Security: If user is only allowed to see a particular subset of some data, then only give them access to a specific subset that exists

3) Logical Independence: Views make your database robust to changes –> underlying structure of database may change, but views keep access consistent