Navigating with Path Expressions

Assume two tables are given as follows: 

CREATE TABLE company (
  companyID  INT NOT NULL,
  name       VARCHAR NOT NULL,
  street     VARCHAR NOT NULL,
  location   VARCHAR NOT NULL,
  president  INT NOT NULL,
  PRIMARY KEY ( companyID ),
  FOREIGN KEY ( president ) REFERENCES employee ( emplno ) );
 

CREATE TABLE vehicle
  vehicleID     INT NOT NULL,
  model         VARCHAR NOT NULL,
  manufacturer  INT NOT NULL,
  color         VARCHAR NOT NULL,
  PRIMARY KEY ( vehicleID ),
  Foreign KEY ( manufacturer ) REFERENCES company ( companyID ) );

Determine the president of the company manufacturing the car with number 93: 

SELECT c.president FROM vehicle v, company c
  WHERE v.vehicleID = 93 AND v.manufacturer = c.companyID
⇓
company: [
  name:       STRING,
  headoffice: address,
  president:  employee ]
 
vehicle: [
  model:        STRING,
  manufacturer: company,
  color:        STRING ]
 

president( manufacturer( v ) ), or name( president( manufacturer( v ) )

OODB languages use expressions (path expressions) which allow evaluation from left to right: 

v.manufacturer.president.name

The dot-notation renders bracketing superfluous.




      Boss: What’s your biggest weakness?    
      Me: Honesty.    
      Boss: I don’t consider that a weakness.    
      Me: I don’t give a f*ck what you think.