Slide 16.10: Equal treatment of attributes and methods

Desired Properties (Cont.)

Equal Treatment of Attributes and Methods
When looking at the properties of an object, one often cannot distinguish between attributes and methods with no parameters.

There is a boolean method deputy with a parameter which allows us to test, for all managers, whether the manager currently under consideration is a deputy:
SELECT a1, a2 FROM a1 IN employee, a2 IN employee WHERE a1.deputy(a2);
Note that method deputy actually has two parameters.

Access to Abstract Types and Classes
The notions of abstract data types are supported in OODBS by the class concepts. Query expressions may refer only to information which is declared as public.

Searches for all persons over the age of 50, supposing that method age is public and determines the age of a person on the basis of the (private) attribute dateofbirth:
SELECT * FROM person WHERE age > 50;

Access to Sets of Objects
A class can be used as

a type, thereby stating the structure and behavior of objects; or
a set of such objects (extension) existing at some point of time.

The following query determines all persons over the age of 50:
SELECT name FROM person WHERE age > 50;
where person denotes both a class and its extension.