Transformation over relations

Revision as of 19:18, 21 August 2013

Relations are altered, replaced, created and deleted by T-rules:

Altering nodes in a relation

Elements of nodes in relations are altered through the operators + (add) and - (delete). The operator + may be omitted.

• rel(%x,A;%y,B):=rel(%x,+C;%y,+D); (add the feature C to %x and D to %y)
• rel(%x,A;%y,B):=rel(%x,C;%y,D);(the same as above)
• rel(%x,A;%y,B):=rel(%x,-A;%y); (delete the feature A from %x)

"strings", [headwords] and [[UWs]] are considered to be features (but a single node may have only one of each)

• rel(%x;%y):=rel(%x,"a";%y); (replace the existing string in %x, if any, by "a")
• rel(%x;%y):=rel(%x,[A];%y);(replace the existing headword in %x, if any, by [A])
• rel(%x;%y):=rel(%x,[[A]];%y); (replace the existing UW in %x, if any, by A)

Creating nodes in a relation

Nodes are created when they are not co-indexed to any node in the left side (see Indexation):

• rel(%x,A;%y,B):=rel(%x;%y;%z,+A); (the node %z, with the feature A, is created as a new argument of the relation rel)

Deleting nodes in a relation

Nodes are deleted when they are not co-indexed to any node in the right side (see Indexation):

• rel(%x,A;%y,B;%z,C):=rel(%x;%y); (the node %z is deleted as an argument of the relation rel)

Nodes are completed deleted if, and only if, they are not part of any other relation

Creating relations

Relations are created by the operator + (add) before the relation to be created. This operator may not be omitted.

• rel(%x;%y):=+rel2(%x;%z); (a new relation rel2 is created between the nodes %x and %z; the original relation is not altered)

Creation of relations is a possible source of infinite loops. In order to prevent the rule from applying eternally, the conditions must be altered:

• rel(%x;%y)^rel2(%x;%z):=:=+rel2(%x;%z);

Deleting relations

Relations are deleted when they are not repeated in the right side, except in case of +

• rel(%x;%y):=; (the relation rel between the nodes %x and %y is deleted)
• rel(%x;%y):=rel2(%x;%y); (the relation rel between %x and %y is deleted and a new relation rel2 is created in its place) (replacement)
• rel(%x;%y):=+rel2(%x;%y); (the relation rel is preserved and a new relation rel2 is created) (creation)

Replacing relations

Relations in the left side are replaced by relations in the right side, except in case of +:

• rel(%x;%y):=rel2(%x;%y); (the relation rel between %x and %y is deleted and a new relation rel2 is created in its place)
• rel1(%x;%y)rel2(%y;%z):=rel3(%x;%z); (the relations rel1 and rel2 are deleted and a new relation rel3 is created in their place) (merge)
• rel(%x;%y):=rel1(%x;%y)rel2(%y;%z); (the relation rel is deleted and two new relations rel1 and rel2 are created in its place) (divide)