fixing structure parentmap

Co-authored-by: Pano Maria <[email protected]>

Author: dachafra

spec/section/joinconditions.md

@@ -57,7 +57,7 @@ A <dfn data-lt="join">join condition</dfn> is represented by a resource that has
 
 * a child map (`rml:childMap`) property, whose value is a [=child map=], or a [=constant-valued expression map=].<br> A <dfn>child map</dfn> (`rml:ChildMap`) is an [=expression map=] which MUST be evaluated against the [=child logical source=]. The <dfn>child logical source</dfn> is the [=logical source=] of the [=triples map=] that contains the [=referencing object map=], i.e. the current [=triples map=]..
 
-* a parent map (`rml:parentMap`) property, whose value is a [=parent map=].<br> A <dfn>parent map</dfn> (`rml:ParentMap`) is an [=expression map=], which MUST be evaluated against the [=parent logical source=]. The <dfn>parent logical source</dfn> is [=logical source=] of the [=referencing object map=]'s [=parent triples map=], i.e. the referenced [=triples map=], or it should have a [=constant value=].
+* a parent map (`rml:parentMap`) property, whose value is a [=parent map=], or a [=constant-valued expression map=].<br> A <dfn>parent map</dfn> (`rml:ParentMap`) is an [=expression map=], which MUST be evaluated against the [=parent logical source=]. The <dfn>parent logical source</dfn> is the [=logical source=] of the [=referencing object map=]'s [=parent triples map=], i.e. the referenced [=triples map=].
 
 If the the [=logical source=] of the [=triples map=] that contains the [=referencing object map=] and the [=logical source=] of the [=referencing object map=]'s [=parent triples map=] are not [=effectively equal=], then the referencing object map MUST have one or more [=join conditions=].