- Added division operator

- Edited parser module to return the fields returned by a division operation
- Edited relation class API, renaming the rearrange method to _rearrange_
- Readline interface specifies that completion works only if supported by the terminal
- Added todo file



git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@240 014f5005-505e-4b48-8d0a-63407b615a7c

CHANGELOG

@@ -104,3 +104,4 @@
 - Organized code so the ui can be either qt or command line
 - Does not depend on QT anymore
 - Added readline user interface
+- Added division operator

TODO

@@ -0,0 +1 @@
+- Convert the relation module to use python's sets

relational/parser.py

@@ -140,6 +140,8 @@ class node (object):
             return list(rels[self.name].header.attributes)
         elif self.kind==BINARY and self.name in ('-','ᑌ','ᑎ'):
             return self.left.result_format(rels)
+        elif self.kind==BINARY and self.name=='÷':
+            return list(set(self.left.result_format(rels)) - set(self.right.result_format(rels)))
         elif self.name=='π':
             l=[]
             for i in self.prop.split(','):

relational/relation.py

@@ -86,7 +86,7 @@ class relation (object):
                 res+=" ".join(r)
             fp.write(res)
         fp.close() #Closing file
-    def rearrange(self,other):
+    def _rearrange_(self,other):
         '''If two relations share the same attributes in a different order, this method
         will use projection to make them have the same attributes' order.
         It is not exactely related to relational algebra. Just a method used 
@@ -201,7 +201,7 @@ class relation (object):
         Will return an empty one if there are no common items.
         Will return None if headers are different.
         It is possible to use projection and rename to make headers match.'''
-        other=self.rearrange(other) #Rearranges attributes' order
+        other=self._rearrange_(other) #Rearranges attributes' order
         if (self.__class__!=other.__class__)or(self.header!=other.header):
             return None
         newt=relation()
@@ -219,7 +219,7 @@ class relation (object):
         Will return an empty one if the second is a superset of first.
         Will return None if headers are different.
         It is possible to use projection and rename to make headers match.'''
-        other=self.rearrange(other) #Rearranges attributes' order
+        other=self._rearrange_(other) #Rearranges attributes' order
         if (self.__class__!=other.__class__)or(self.header!=other.header):
             return None
         newt=relation()
@@ -230,6 +230,19 @@ class relation (object):
             if e not in other.content:
                 newt.content.append(list(e))
         return newt
+    def division(self,other):
+        '''Division operator
+        The division is a binary operation that is written as R ÷ S. The
+        result consists of the restrictions of tuples in R to the
+        attribute names unique to R, i.e., in the header of R but not in the
+        header of S, for which it holds that all their combinations with tuples
+        in S are present in R. 
+        '''
+        d_headers=list(set(self.header.attributes) - set(other.header.attributes))
+        t=self.projection(d_headers).product(other)
+        u = t.difference(self)
+        v = u.projection(d_headers)
+        return self.projection(d_headers).difference(v)
         
     def union(self,other):
         '''Union operation. The result will contain items present in first
@@ -238,7 +251,7 @@ class relation (object):
         Will not insert tuplicated items.
         Will return None if headers are different.
         It is possible to use projection and rename to make headers match.'''
-        other=self.rearrange(other) #Rearranges attributes' order
+        other=self._rearrange_(other) #Rearranges attributes' order
         if (self.__class__!=other.__class__)or(self.header!=other.header):
             return None
         newt=relation()
@@ -372,7 +385,7 @@ class relation (object):
     def __eq__(self,other):
         '''Returns true if the relations are the same, ignoring order of items.
         This operation is rather heavy, since it requires sorting and comparing.'''
-        other=self.rearrange(other) #Rearranges attributes' order so can compare tuples directly
+        other=self._rearrange_(other) #Rearranges attributes' order so can compare tuples directly
         if (self.__class__!=other.__class__)or(self.header!=other.header):
             return False #Both parameters must be a relation
         
@@ -549,6 +562,3 @@ class header (object):
                     res.append(j)
         return res
         
-
-if __name__=="__main__":
-  pass

relational_readline/linegui.py

@@ -265,7 +265,7 @@ def exec_query(command):
     
 def main(files=[]):
     print "> ; Type HELP to get the HELP"
-    print "> ; Completion is activated using the tab"
+    print "> ; Completion is activated using the tab (if supported by the terminal)"
     
     for i in files:
         load_relation(i)