0f8d0b68ac
git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@17 014f5005-505e-4b48-8d0a-63407b615a7c
129 lines
3.3 KiB
Python
129 lines
3.3 KiB
Python
# coding=UTF-8
|
||
# Relation
|
||
# Copyright (C) 2008 Salvo "LtWorf" Tomaselli
|
||
#
|
||
# Relation is free software: you can redistribute it and/or modify
|
||
# it under the terms of the GNU General Public License as published by
|
||
# the Free Software Foundation, either version 3 of the License, or
|
||
# (at your option) any later version.
|
||
#
|
||
# This program is distributed in the hope that it will be useful,
|
||
# but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
# GNU General Public License for more details.
|
||
#
|
||
# You should have received a copy of the GNU General Public License
|
||
# along with this program. If not, see <http://www.gnu.org/licenses/>.
|
||
#
|
||
# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
|
||
def parse(expr):
|
||
'''This function parses a relational algebra expression, converting it into python,
|
||
executable by eval function to get the result of the expression.'''
|
||
symbols=("σ","π","ρ")
|
||
|
||
expr=expr.strip()
|
||
|
||
print "====PARSING: ",expr
|
||
|
||
start=-1
|
||
end=-1
|
||
parenthesis=0
|
||
lexpr=list(expr)
|
||
#Parses the string from end to begin
|
||
for i in range(len(lexpr)):
|
||
if lexpr[i]=="(":
|
||
if parenthesis==0:
|
||
start=i+1
|
||
parenthesis+=1
|
||
elif lexpr[i]==")":
|
||
parenthesis-=1
|
||
if parenthesis==0:
|
||
end=i
|
||
break
|
||
|
||
if start==-1: #No complex operators
|
||
return parse_op(expr)
|
||
else:
|
||
#internal=expr[0:start]+ parse(expr[start:end])+expr[end:]
|
||
internal=parse(expr[start:end])
|
||
print "EXPRESSION: %s" % (internal)
|
||
|
||
endp=start-1
|
||
start=-1
|
||
symbol=""
|
||
for i in range(endp,-1,-1):
|
||
if expr[i:i+2] in symbols:
|
||
symbol=expr[i:i+2]
|
||
start=i+2
|
||
break
|
||
parameters=expr[start:endp]
|
||
print "===Internal: %s\t Parameters: %s" %(internal,parameters)
|
||
|
||
|
||
res=""
|
||
if symbol=="π":#Projection
|
||
params=""
|
||
count=0
|
||
for i in parameters.split(","):
|
||
if count!=0:
|
||
params+=","
|
||
else:
|
||
count=1
|
||
params+="\"%s\"" % (i.strip())
|
||
|
||
res="%s.projection(%s)" % (internal,params)
|
||
elif symbol== "σ": #Selection
|
||
res="%s.selection(\"%s\")" % (internal,parameters)
|
||
elif symbol=="ρ": #Rename
|
||
params=parameters.replace(",","\",\"").replace("➡","\",\"")
|
||
res="%s.rename(\"%s\")" % (internal,params)
|
||
print res
|
||
res= ("%s%s%s") % (expr[0:start-2],res.replace(" ",""),expr[end+1:])
|
||
return parse_op(res)
|
||
#Selection σage > 25 Λ rank = weight(A)
|
||
#Projection Q ᐅᐊ π a,b(A) ᐅᐊ B
|
||
#Rename ρid➡i,name➡n(A)
|
||
#π a,b(π a,b(A))
|
||
#ρid➡i,name➡n(π a,b(A))
|
||
#A ᐅᐊ B
|
||
|
||
|
||
|
||
def parse_op(expr):
|
||
'''This function parses a relational algebra expression including only operators
|
||
(not functions) and no parenthesis, converting it into python,
|
||
executable by eval function to get the result of the expression.'''
|
||
|
||
result=""
|
||
symbols={}
|
||
symbols["*"]=".product(%s)"
|
||
symbols["-"]=".difference(%s)"
|
||
symbols["ᑌ"]=".union(%s)"
|
||
symbols["ᑎ"]=".intersection(%s)"
|
||
symbols["ᐅᐊ"]=".join(%s)"
|
||
symbols["ᐅᐊLEFT"]=".outer_left(%s)"
|
||
symbols["ᐅᐊRIGHT"]=".outer_right(%s)"
|
||
symbols["ᐅᐊFULL"]=".outer(%s)"
|
||
|
||
for i in symbols:
|
||
expr=expr.replace(i,"_____%s_____"% (i))
|
||
|
||
tokens=expr.split("_____")
|
||
|
||
i=0;
|
||
tk_l=len(tokens)
|
||
while i<tk_l:
|
||
if tokens[i] not in symbols:
|
||
result+=tokens[i].strip()
|
||
else:
|
||
|
||
result+=symbols[tokens[i]] % (tokens[i+1].strip())
|
||
i+=1
|
||
i+=1
|
||
return result
|
||
|
||
if __name__=="__main__":
|
||
while True:
|
||
e=raw_input("Expression: ")
|
||
print parse(e)
|
||
|