Transformation over nodes

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Altering nodes

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

  • (%x,A):=(%x,+B); (add the feature B to %x)
  • (%x,A):=(%x,B); (the same as above: add the feature B to %x)
  • (%x,A):=(%x,-A); (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)

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

Example:

  • ("a",[a],[[a]],A,C,%x):=("b",[b],[[b]],-A,+B,%x); (the original node ("a",[a],[[a]],A,C) becomes ("b",[b],[[b]],B,C). Note that the feature C is preserved, because it was not affected by the rule);

Deleting nodes

In linear rules, nodes are deleted if they are not repeated (co-indexed) in the right side:

  • (%x)(%y):=(%x); (the node %y will be deleted)

In other rules, nodes are deleted if they are not repeated (co-indexed) in the right side and are not part of any other relation:

  • rel(%x;%y):=rel(%x); (the node %y will be deleted if, and only if, it is not part of any other relation)

Creating nodes

Nodes are created through the use of new indexes in the right side:

  • ("a",%x)("b",%y):=(%x)(%y)("c",%z); (the node %z will be created)
  • ("a",%x)("b",%y):=(%x)("c",%z); (the node %z will be created, and %b will be deleted)

Duplicating (cloning) nodes

Nodes may be duplicated by repeating indexes on the right side along with the command #CLONE:

  • ("a",^CLONED,%x):=(%x,+CLONED)(%x,+CLONED,#CLONE);
    ("a") becomes ("a")("a")

In order to avoid infinite recursion, it is important to change the condition on the right side (in the example above, the feature +CLONED, assigned to all instances of the clone, prevents the rule from applying indefinitely)
Clones contain the same elements of the original nodes, unless they are explicitly altered during the cloning:

  • ("a",[a],[[a]],A,^CLONED,%x):=(%x,+CLONED)(%x,+CLONED,#CLONE);
    ("a",[a],[[a]],A) becomes ("a",[a],[[a]],A,CLONED)("a",[a],[[a]],A,CLONED)
  • (A,^CLONED,%x):=(%x,-A,+B,+CLONED)(%x,-A,+C,+CLONED,#CLONE);
    (A) becomes (B,CLONED)(C,CLONED)

Splitting nodes

One node may be split into two or more nodes through the use of splitting rules. Consider, for instance, the cases below:

Splitting rules deal only with strings and apply only to nodes with the feature TEMP.
Original node: ("abc",TEMP)
Split rule: ("abc"):=("ab")("c");
Resulting nodes: ("ab",TEMP)("c",TEMP);
However, if the original node was ("abc"), without TEMP, the rule would not have been applied (i.e., it is necessary to assign the feature TEMP to the node before splitting it)
Splitting rules are conservative: the elements of the original node, except the string, will be preserved unless explicitly altered.
Original node: ("abc",[abc],[[abc]],A,B,C,TEMP)
Split rule: ("abc"):=("ab")("c");
Resulting nodes: ("ab",[abc],[[abc]],A,B,C,TEMP)("c",[abc],[[abc]],A,B,C,TEMP) (i.e., the elements of the original node will be copied to the new nodes)
However, if the rule was: ("abc"):=("ab",-A,-B,-C,-TEMP,+AB)("c",-TEMP);
The result would be: ("ab",[abc],[[abc]],AB)("c",[abc],[[abc]],C,TEMP)

Merging nodes (&)

Two or more nodes may be merged by the command &:

  • (%x)(%y)(%z):=(%x&%y&%z);

In the example above("a")("b")("c") becomes ("abc")

Merge operations concatenate headwords and UWs, and join features

("hw1",[[uw1]],F1,%x)("hw2",[[uw2]],F2,%y)("hw3",[[uw3]],F3,%z):=(%x&%y&%z);
The resulting node is ("hw1hw2hw3",[[uw1uw2uw3]],F1,F2,F3)

Compare the difference
  • (%x)(%y):=(%z); (the nodes %x and %y are replaced by %z, and their features are lost unless explicitly included in %z)
  • (%x)(%y):=(%x&%y); (the nodes %x and %y are merged)

Retrieving entries in the dictionary after tokenization (?)

During transformation (i.e., after tokenization), dictionary entries may be accessed from transformation rules by the command "?"

  • (?[headword]) retrieves the first entry in the dictionary with the headword "headword"
  • (?[[uw]]) retrieves the first entry in the dictionary with the UW "uw"
  • (?[headword],?[[uw]],?feature) retrieves the first entry in the dictionary with the headword "headword", the UW "uw" and the feature "feature"

Regular expressions, variables and disjunction may also be used in dictionary search

  • (?[/abcd./]) retrieves the first entry in the dictionary whose headword has 5 characters and begins with "abcd" (this works only in natural language generation)
  • (?[[/abcd./]]) retrieves the first entry in the dictionary whose UW has 5 characters and begins with "abcd" (this works only in natural language analysis)
Obligatory parameters
Due to the indexation algorithm, the headword is obligatory in IAN and the UW is obligatory in EUGENE:
  • (?[headword]) will work only in IAN
  • (?[[uw]]) will work only in EUGENE
  • (?feature) will not work in IAN or EUGENE
Variables
In order to avoid repetition, dictionary look-up may use the values of indexed nodes in the left side
  • (?[%x]) retrieves the first entry in the dictionary with the same headword of the node %x
  • (?[[%x]]) retrieves the first entry in the dictionary with the same UW of the node %x
  • (?[%x],ATT=%x) retrieves the first entry in the dictionarz with the same headword of the node %x and whose attribute ATT has the same value of the attribute ATT of the node %x
Example

Dictionary search is used mainly in natural language generation

  • (N,NUM,GEN,@def,%noun):=(?[[]],?ART,?DEF,?NUM=%noun,?GEN=%noun)(%noun,-@def);

In case of node %noun with the features noun (N), number (NUM) and gender (GEN), and with the attribute @def (definite), search the first entry in the dictionary associated with the UW "" (empty UW) with the features ART and DEF, and whose attributes NUM and GEN have the same values of the ones of the node %noun, and insert it in front of the noun. Remove @def from the noun in order to avoid an infinite loop.

Triggering rules (!)

Inflectional rules are triggered in the grammar by the command "!"<ATTRIBUTE>.
Given the dictionary entry:

  • [foot] "foot" (POS=NOU, NUM(PLR:="oo":"ee")) <eng,0,0>;

The rule NUM(PLR:="oo":"ee") is triggered by !NUM
For instance:

  • (NUM=PLR,^inflected):=(!NUM,+inflected); or
  • (PLR,^inflected):=(!NUM,+inflected); or
  • (NUM,^inflected):=(!NUM,+inflected);

In the first case (NUM=PLR), the system verifies if the attribute "NUM" is set and if it has the value "PLR". In the second and in the third case, the system simply verifies if the word has any feature (attribute or value) equal to "PLR" or "NUM".
It's important to stress that, as the features of the dictionary are defined by the user, there is no way of pre-assigning attribute-value pairs. In that sense, it's not possible to infer that "PLR" will be a value of the attribute "NUM" except through an assignment of the form "NUM=PLR" (i.e., given only "PLR" or "NUM", is not possible to state "NUM=PLR").

Software