8.20  See lecture notes for definition.

      Compatible: INVENTORY(ProdCode, ProdDesc, Price)
                  ORDER(ProdCode, ProdDesc, Price)

      Non-compatible: INVENTORY(ProdCode, ProdDesc, Price)
                      ORDER(ProdCode, ProdDesc, Quantity)

      Note that the attributes Price and Quantity are unlikely to have
      the same domain and so would be incompatible.


8.21  Let the following tables be instances of the MANUFACTURERS and
      COMPANY relations:

      COMPANY          Name  NumberEmployees     Sales
                       -------------------------------
                       IBM             50000   9000000
                       NEC             80000  15000000
                       COMPUSA          9000   3000000
                                    
      MANUFACTURERS    Name   PeopleCount   Revenue
                       ----------------------------
                       IBM          50000   9000000
                       NEC          80000  15000000
                                    

      An example of UNION:

         COMPANY[Name] + MANUFACTURERS[Name]

                       Name   
                       -------
                       IBM   
                       NEC  
                       COMPUSA 

                                    
8.22 An example of DIFFERENCE:

         COMPANY[Name] - MANUFACTURERS[Name]

                       Name   
                       -------
                       COMPUSA
    
                                
8.23 An example of INTERSECTION:

         COMPANY[Name] INTERSECT MANUFACTURERS[Name]

                       Name  
                       ----
                       IBM 
                       NEC
                                    

8.24 The product contains 42 tuples and so only the first eight are 
     presented below:

     Name   Salary  Number  CustName               SalespersonName  Amount
     ---------------------------------------------------------------------
     Abel   120000     100  Abernathy Construction      Zenith         560
     Abel   120000     200  Abernathy Construction       Jones        1800
     Abel   120000     300  Manchester Lumber             Abel         480
     Abel   120000     400  Amalgamated Housing           Abel        2500
     Abel   120000     500  Abernathy Construction      Murphy        6000
     Abel   120000     600  Tri-City Builders             Abel         700
     Abel   120000     700  Manchester Lumber            Jones         150
     Baker   42000     100  Abernathy Construction      Zenith         560


8.25 Name   Salary
     -------------
     Abel   120000 
     Baker   42000 
     Jones   36000 
     Murphy  50000 
     Zenith 118000 
     Kobad   34000 

     Salary
     ------
     120000 
      42000 
      36000 
      50000 
     118000 
      34000 

     If two salespersons have the same salary then the operation
     would result in a relation with fewer tuples since duplicate 
     tuples are removed.


8.26 a) SALESPERSON WHERE Name = 'Kobad'
     b) SALESPERSON WHERE Salary > 55000
     c) SALESPERSON WHERE Name = 'Zenith' AND Salary > 90000

8.27 SALESPERSON JOIN (Name=SalespersonName) ORDER


8.28 a) SALESPERSON [Name]
     b) ORDER [SalespersonName]
     c) SALESPERSON [Name] - ORDER [SalespersonName]
     d) (ORDER WHERE CustName = 'Abernathy Construction') [SalespersonName]
     e) (SALESPERSON JOIN (Name=SalespersonName) 
             (ORDER WHERE CustName='Abernathy Construction')) [Salary]