JOHN - A Knowledge Representation Language

General Expressions

The property values? for objects can be queried by specifying the instance name followed by the property name. As in the second example below, this can be a cascaded list of property names. Here roby position col really implies ((roby position) col ), meaning first to derive the instance name from the roby position query, and then asking the col property of the result.

    > A3 col
   colA 
   > roby position
   A3
   > roby position col
   colA 

The properties for a set of instances can similarly be queried, resulting in a new set containing the property values. As in above, the list of properties can come in cascaded form.

   > all row
   { row1, row2, row3, row4 }
   > all row number
   { 1, 2, 3, 4 }  
   > { A3 B4 } col.
   { colA, colB } 
   > { A3 B4 } col letter.
   { A, B } 

These expressions can be combined with the primitive expressions described in previous sections.

    > C4 col letter + U.
   CU
    > row5 number * 7.
   35 

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