55 lines
1.8 KiB
Python
55 lines
1.8 KiB
Python
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# coding=UTF-8
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# Relational
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# Copyright (C) 2008 Salvo "LtWorf" Tomaselli
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#
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# Relation is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
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'''This module optimizes relational expressions into ones that require less time to be executed'''
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RELATION=0
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UNARY=1
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BINARY=2
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class node (object):
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'''This class is a node of a relational expression. Leaves are relations and internal nodes are operations.'''
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def __init__(self,expression):
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'''expression must be a valid relational algrbra expression that would be accepted by the parser
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and must be utf16'''
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self.kind=0
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self.name="a"
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self.prop=""
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'''*-ᑌᑎᐅᐊᐅLEFTᐊᐅRIGHTᐊᐅFULLᐊπσρ'''
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'''(a ᑌ (a ᑌ b ᑌ c ᑌ d)) ᑎ c - σ i==3(πa,b(aᑌ b ᑎ c))'''
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for i in list(expression):
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print i
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def __str__(self):
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if (self.kind==RELATION):
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return self.name
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elif (self.kind==UNARY):
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return self.name + " "+ self.prop+ " (" + self.child +")"
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elif (self.kind==BINARY):
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return "("+ self.left + ") " + self.name + " (" + self.right+ ")"
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n=node(u"(a ᑌ b) ᑌ c ᑌ d")
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print n
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