Slide 16.9: Explicit join

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Slide 16.8: Desirable properties
Slide 16.10: Equal treatment of attributes and methods
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Desired Properties (Cont.)

Access to Complex Objects (Cont.)

Searches for all blue vehicles manufactured by Ford:
SELECT * FROM vehicle WHERE color='Blue' AND manufacturer.name='Ford';
The manufacturer value is an object identity from the class company. Access to the attributes of this referenced object is using a path expression.

Searches for all companies whose head-office address is identical to the address of its president:
SELECT * FROM company WHERE headoffice==president.domicile;
Object identity (rather than value identity) will be tested by using“==”. Using ‘=‘. will test the equality of values:
SELECT * FROM company WHERE headoffice.location=president.domicile.location;

Explicit Join
With the help of path expressions, predefined relationships between objects can be traversed.

Looks for persons and vehicles where the name of the person is identical to the name of the president of the company that manufactures the car:
SELECT p,f FROM p IN person, f IN vehicle WHERE p.name=f.manufacturer.president.name;

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Slide 16.8: Desirable properties
Slide 16.10: Equal treatment of attributes and methods
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Interviewer: Your resume says you’re very quick at maths.
Me: Yes I am!
Interviewer: Whats 12 x 37?
Me: 49.
Interviewer: That’s not even close!
Me: Yeah, but it was fast.