spa2rql.py
author Sylvain Thénault <sylvain.thenault@logilab.fr>
Wed, 23 Sep 2009 09:35:28 +0200
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remove method deprecated since 3.2
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"""SPARQL -> RQL translator
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:organization: Logilab
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:copyright: 2009 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
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:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
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:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
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"""
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from logilab.common import make_domains
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from rql import TypeResolverException
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from fyzz.yappsparser import parse
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from fyzz import ast
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from cubicweb.xy import xy
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class UnsupportedQuery(Exception): pass
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def order_limit_offset(sparqlst):
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    addons = ''
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    if sparqlst.orderby:
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        sortterms = ', '.join('%s %s' % (var.name.upper(), ascdesc.upper())
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                              for var, ascdesc in sparqlst.orderby)
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        addons += ' ORDERBY %s' % sortterms
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    if sparqlst.limit:
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        addons += ' LIMIT %s' % sparqlst.limit
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    if sparqlst.offset:
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        addons += ' OFFSET %s' % sparqlst.offset
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    return addons
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class QueryInfo(object):
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    """wrapper class containing necessary information to generate a RQL query
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    from a sparql syntax tree
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    """
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    def __init__(self, sparqlst):
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        self.sparqlst = sparqlst
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        if sparqlst.selected == ['*']:
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            self.selection = [var.upper() for var in sparqlst.variables]
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        else:
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            self.selection = [var.name.upper() for var in sparqlst.selected]
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        self.possible_types = {}
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        self.infer_types_info = []
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        self.union_params = []
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        self.restrictions = []
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        self.literals = {}
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        self._litcount = 0
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    def add_literal(self, value):
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        key = chr(ord('a') + self._litcount)
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        self._litcount += 1
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        self.literals[key] = value
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        return key
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    def set_possible_types(self, var, varpossibletypes):
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        """set/restrict possible types for the given variable.
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        :return: True if something changed, else false.
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        :raise: TypeResolverException if no more type allowed
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        """
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        varpossibletypes = set(varpossibletypes)
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        try:
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            ctypes = self.possible_types[var]
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            nbctypes = len(ctypes)
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            ctypes &= varpossibletypes
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            if not ctypes:
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                raise TypeResolverException()
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            return len(ctypes) != nbctypes
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        except KeyError:
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            self.possible_types[var] = varpossibletypes
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            return True
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    def infer_types(self):
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        # XXX should use something similar to rql.analyze for proper type inference
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        modified = True
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        # loop to infer types until nothing changed
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        while modified:
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            modified = False
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            for yams_predicates, subjvar, obj in self.infer_types_info:
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                nbchoices = len(yams_predicates)
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                # get possible types for the subject variable, according to the
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                # current predicate
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                svptypes = set(s for s, r, o in yams_predicates)
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                if not '*' in svptypes:
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                    if self.set_possible_types(subjvar, svptypes):
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                        modified = True
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                # restrict predicates according to allowed subject var types
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                if subjvar in self.possible_types:
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                    yams_predicates = [(s, r, o) for s, r, o in yams_predicates
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                                       if s == '*' or s in self.possible_types[subjvar]]
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                if isinstance(obj, ast.SparqlVar):
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                    # make a valid rql var name
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                    objvar = obj.name.upper()
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                    # get possible types for the object variable, according to
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                    # the current predicate
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                    ovptypes = set(o for s, r, o in yams_predicates)
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                    if not '*' in ovptypes:
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                        if self.set_possible_types(objvar, ovptypes):
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                            modified = True
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                    # restrict predicates according to allowed object var types
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                    if objvar in self.possible_types:
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                        yams_predicates = [(s, r, o) for s, r, o in yams_predicates
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                                           if o == '*' or o in self.possible_types[objvar]]
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                # ensure this still make sense
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                if not yams_predicates:
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                    raise TypeResolverException()
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                if len(yams_predicates) != nbchoices:
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                    modified = True
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    def build_restrictions(self):
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        # now, for each predicate
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        for yams_predicates, subjvar, obj in self.infer_types_info:
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            rel = yams_predicates[0]
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            # if there are several yams relation type equivalences, we will have
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            # to generate several unioned rql queries
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            for s, r, o in yams_predicates[1:]:
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                if r != rel[1]:
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                    self.union_params.append((yams_predicates, subjvar, obj))
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                    break
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            # else we can simply add it to base rql restrictions
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            else:
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                restr = self.build_restriction(subjvar, rel[1], obj)
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                self.restrictions.append(restr)
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   123
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    def build_restriction(self, subjvar, rtype, obj):
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        if isinstance(obj, ast.SparqlLiteral):
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            key = self.add_literal(obj.value)
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            objvar = '%%(%s)s' % key
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        else:
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            assert isinstance(obj, ast.SparqlVar)
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            # make a valid rql var name
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            objvar = obj.name.upper()
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        # else we can simply add it to base rql restrictions
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        return '%s %s %s' % (subjvar, rtype, objvar)
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   134
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    def finalize(self):
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        """return corresponding rql query (string) / args (dict)"""
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        for varname, ptypes in self.possible_types.iteritems():
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            if len(ptypes) == 1:
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                self.restrictions.append('%s is %s' % (varname, iter(ptypes).next()))
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        unions = []
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        for releq, subjvar, obj in self.union_params:
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            thisunions = []
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            for st, rt, ot in releq:
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                thisunions.append([self.build_restriction(subjvar, rt, obj)])
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                if st != '*':
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                    thisunions[-1].append('%s is %s' % (subjvar, st))
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                if isinstance(obj, ast.SparqlVar) and ot != '*':
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                    objvar = obj.name.upper()
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                    thisunions[-1].append('%s is %s' % (objvar, objvar))
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            if not unions:
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                unions = thisunions
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            else:
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                unions = zip(*make_domains([unions, thisunions]))
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        selection = 'Any ' + ', '.join(self.selection)
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        sparqlst = self.sparqlst
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        if sparqlst.distinct:
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            selection = 'DISTINCT ' + selection
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        if unions:
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            baserql = '%s WHERE %s' % (selection, ', '.join(self.restrictions))
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            rqls = ['(%s, %s)' % (baserql, ', '.join(unionrestrs))
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                    for unionrestrs in unions]
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            rql = ' UNION '.join(rqls)
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            if sparqlst.orderby or sparqlst.limit or sparqlst.offset:
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                rql = '%s%s WITH %s BEING (%s)' % (
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                    selection, order_limit_offset(sparqlst),
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                    ', '.join(self.selection), rql)
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   167
        else:
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            rql = '%s%s WHERE %s' % (selection, order_limit_offset(sparqlst),
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                                      ', '.join(self.restrictions))
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        return rql, self.literals
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   171
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   172
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class Sparql2rqlTranslator(object):
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    def __init__(self, yschema):
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        self.yschema = yschema
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   176
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    def translate(self, sparql):
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        sparqlst = parse(sparql)
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        if sparqlst.type != 'select':
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   180
            raise UnsupportedQuery()
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        qi = QueryInfo(sparqlst)
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   182
        for subj, predicate, obj in sparqlst.where:
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   183
            if not isinstance(subj, ast.SparqlVar):
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   184
                raise UnsupportedQuery()
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   185
            # make a valid rql var name
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            subjvar = subj.name.upper()
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   187
            if predicate == ('', 'a'):
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   188
                # special 'is' relation
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   189
                if not isinstance(obj, tuple):
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   190
                    raise UnsupportedQuery()
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   191
                # restrict possible types for the subject variable
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   192
                qi.set_possible_types(
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   193
                    subjvar, xy.yeq(':'.join(obj), isentity=True))
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   194
            else:
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                # 'regular' relation (eg not 'is')
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   196
                if not isinstance(predicate, tuple):
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   197
                    raise UnsupportedQuery()
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   198
                # list of 3-uple
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   199
                #   (yams etype (subject), yams rtype, yams etype (object))
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   200
                # where subject / object entity type may '*' if not specified
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   201
                yams_predicates = xy.yeq(':'.join(predicate))
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   202
                qi.infer_types_info.append((yams_predicates, subjvar, obj))
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                if not isinstance(obj, (ast.SparqlLiteral, ast.SparqlVar)):
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                    raise UnsupportedQuery()
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   205
        qi.infer_types()
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        qi.build_restrictions()
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        return qi