# Index

Indexes (%) are used for co-indexing nodes in T-rules and D-rules.

## Use

Indexes are used in T-rules and D-rules.

### T-rules

In T-rules, indexes are used:

• to associate nodes in the left side of the rule (CONDITION) to nodes in the right side of the rule (ACTION):
• (%a)(%b)(%c):=(%b); (delete the first and the third nodes, and keep the second)
• (%a)(%b)(%c):=(%c)(%b)(%a); (reverse the order)
• rel(%a;%b;%c):=rel(%a;%b); (remove the third argument of the relation rel)
• rel(%a;%b;%c):=rel(%c;%b;%a); (reverse the order of the arguments of the relation rel)
• to associate nodes within the left side of the rules
• (%a)(%b)(%a):=(%b); (delete the first and the third nodes, if they are the same)
• rel1(%a;%b)rel2(%a;%c):=rel3(%a;%c); (replace the relations rel1 and rel2 by the relation rel3 if the first argument of rel1 is the first argument of rel2)
• to copy values of attributes between nodes
• (%a)(%b):=(%a)(%b,GEN=%a); (copy the value of the attribute GEN from the node %a to the node %b if the node %b comes after the node %a)
• NA(%a;%b):=NA(%a;%b,GEN=%a); (copy the value of the attribute GEN from the node %a to the node %b if there is a relation NA between them)
• to test values of attributes within the left side of the rules
• (%a)(%b,GEN=%a):=; (delete the nodes %a and %b if they have the same value of the attribute GEN)
• rel1(%a;%b,GEN=%b):=rel2(%a;%b); (replace the relation rel1 by rel2 if the arguments of rel1 have the same value of the attribute GEN)

### D-rules

In D-rules, indexes are used to test values of attributes within the left side of the rules

• (%a,ART)(%b,NOU,GEN=%a)=1; (nouns following articles normally have the same gender of the article)

## Syntax

Indexes are made of any sequence of alphanumeric characters and underscore preceded by % and starting by alphabetic characters:

%index
%a
%first_index
%a1
%first index (no blank spaces are allowed)
%03 (numeric characters cannot be used as user-defined indexes)

## Default Indexation

If not explicitly informed, indexation is done automatically by the machine, as follows:

• if the number of nodes is the same in the left and in the right side, NODES ARE CO-INDEXED, starting from left to right
("a")("b")("c"):=("d")("e")("f"); is the same as ("a",%01)("b",%02)("c",%03):=("d",%01)("e",%02)("f",%03); (i.e., "a" will be replaced by "d", "b" by "e", and "c" by "f")
rel("a";"b";"c"):=rel("d";"e";"f"); is the same as rel("a",%01;"b",%02;"c",%03):=rel("d",%01;"e",%02;"f",%03);
• if the number of nodes is not the same in both sides, NODES ARE NOT CO-INDEXED
("a")("b")("c"):=("d")("e"); is the same as ("a",%01)("b",%02)("c",%03):=("d",%04)("e",%05); (i.e., "a", "b" and "c" will be deleted, and "d" and "e" will be created)
rel("a";"b";"c"):=rel("d";"e"); is the same as rel("a",%01;"b",%02;"c",%03):=rel("d",%04;"e",%05);

Default indexes are also assigned to hyper-nodes and sub-nodes by the notation <PARENT NODE><CHILD NODE>, where <PARENT NODE> may be, itself, a sub-node:

• (((A))):=(((B))); is the same as (%01(%01%01(%01%01%01,A))):=(%01(%01%01(%01%01%01,B)));
• X(Y(A;B);C) is the same as X(%01,Y(%01%01,A;%01%02,B);%02)
• %01 = Y(A;B), %02 = C, %01%01 = A, %01%02 = B
• X(Y(Z(A;B);C);D) is the same as X(%01,Y(%01%01,Z(%01%01%01,A;%01%01%02,B);%01%02,C);%02,D)
• %01 = Y(Z(A;B);C), %02 = D, %01%01 = Z(A;B), %01%02 = C, %01%01%01 = A, %01%01%02 = B

In order to avoid ambiguities, it is highly recommended that indexes are replaced by user-defined labels made of any sequence of alphabetic characters and underscore:

## Observations

1. Non-indexed nodes in the right side means ADDITION, whereas left-side nodes that are not referred to in the right side means DELETION
X(%a;%b):=Y(%a;X;%b); is the same as X(%a;%b):=Y(%a;%02,X,;%b); (it means that a new node with the feature X will be created for the relation Y)
X(%a;%b;%c):=Y(%a;%c); (it means that the second node of X will be deleted from the relation Y)
2. Any co-indexation is made by the use of indexes and not by the repetition of features.
'X(A;)Y(A;) is different from X(%a;)Y(%a;).
In the former case, the first node of X is not necessarily the first node of Y, they only share the same feature A; in the latter case, the first node of X is necessarily the first node of Y.</blockquote>