Changes between Version 20 and Version 21 of FunctionalDependencies


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Timestamp:
Apr 13, 2006 12:34:38 AM (8 years ago)
Author:
ross@…
Comment:

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  • FunctionalDependencies

    v20 v21  
    137137== Proposed Fixes == 
    138138 
    139 The following are alternatives. 
     139The following are alternatives, based on different analyses of the above confluence problem. 
    140140 
    141141=== Modified coverage condition === 
     
    149149    either 
    150150    * any variable occurring free in t,,Y,, must also occur free in t,,X,,, or 
    151     * the functional dependency is ''full'' (involves all the arguments of the class), and the arguments t,,Y,, are type variables determined by the free variables of t,,X,,. 
     151    * the functional dependency is ''full'' (involves all the arguments of the class), and the arguments t,,Y,, are distinct type variables determined by the free variables of t,,X,,. 
    152152 
    153153The fullness condition restores confluence, while the variable argument condition restores termination. 
     
    168168 
    169169To guarantee termination, we would need to require that for any instance C t, each argument is either covered by t,,X,, or is a single variable. 
     170 
     171=== Modified instance reduction === 
     172 
     173Another possibility is to modify instance reduction to record the functional dependency on the constraint being reduced (see [http://www.cs.kent.ac.uk/~cr3/chr/Tc2CHR.hs]). 
     174 
     175----------------------------------------------------------------------------------