Slide 16.15: Generating new classes, instances, and operations

Desired Properties (Cont.)

Generating New Classes, Instances, and Operations (Cont.)

Creates a view table, called studentcourses, that lists student names and sid values with course names and cno values for courses in which they are enrolled.

CREATE VIEW studentcourses( sname, sid, cname, cno ) AS
  SELECT s.sname, s.sid, c.cname, c.cno
    FROM students s, courses c, enrollment e
    WHERE e.cno = c.cno AND e.sid = s.sid;

Define a view in which person objects, their name values and vehicles manufactured by Ford are to be interrelated in such a way that for each tuple the name of the person and the name of the company‘.s president correspond.
CREATE CLASS k AS SELECT p, p.name, f FROM p IN person, f IN vehicle WHERE f.manufacturer.name = 'Ford' AND p.name = f.manufacturer.president.name;
⇓
{[ p:person, name:STRING, f:vehicle ]}
Two kinds of view formation are
1. Object-preserving: Views introduce no new object identities, because they constitute derived data and objects. The identities of the persons could be used. The problem from this approach is
  {[ p:person, name:STRING, f:{vehicle} ]}
2. Object-generating: The dynamic generation of object identities for objects that are to be included in the result of a query. Need to be clarified how the new class is to be integrated into the already existing class hierarchy.