3.1 Common grammatical rules

To handle many languages in multilingual machine translation system, common grammatical rules should explain linguistic phenomena of as many countries as possible. For explanation of linguistic phenomena of configurational language (e.g. English) as well as nonconfigurational languages (e.g. Korean, Japanese, German) whose word order is relatively free, we have made new grammar rules where X-bar syntactic theory[Jackendoff 1977] and HPSG [Pollard 1994] were mixed. The new grammar was made in binary structure except the coordination structure which was made in triple structure.

Table 1. Common grammar rules
	head-final-structure	head-first-structure	head-middle-structure
1	PRED => ARG PRED	PRED => PRED ARG	COORD => ARG1 COORD ARG2
2	MODED => MOD MODED	MODED => MODED MOD
3	FUNCT => ARG FUNCT	FUNCT => FUNCT ARG

The common grammar rules of the table 1 are described in Appendix 1 according to the notation of the CAT2 machine translation system.

3.2 Common lexicon information structure

We need to make the lexicon information structure in order to input, manage and correct consistently the lexicon information of the multilingual machine translation system. It is desirable to build not monotonic, but multiple structure so that the information structure of lexicon may represent the possible linguistic information and be moved collectively. From this point of view I have selected the feature structure as the multilingual lexicon information structure and made the attributes be the same in many languages. Appendix 2 shows an example of multilingual lexicon information structure.

3.3 Common structural transfer rules

There is also the part in the transfer process the many languages can share. It is the compositional transfer that copies the node of the source language to that of the target language if the analysis structure of the former and the generation structure of the latter are the same. We make use of the method deleting the functional words and then transforming the syntactic nodes to the 'predicate-argument-modifier' nodes in our multilingual machine translation system in order to transfer compositionally the different structures between the languages. We have recorded the noncompositional structural rules unusable to the common structural transfer rules in the transfer lexicon because they depend on the lexemes. The transfer rules have the priority order: the noncompositional structural transfer rules are applied first to the transfer process, second, the common structural transfer rules and last, the lexical transfer rules in the lexicon. The following rule shows the common structural transfer rule:
(1) common_structural_transfer_rule = {}.[+node] <=> {}.[+node]. The rule (1) says that all compositional transfer trees, that is, '+node' are transferred unvaryingly from the source language to the target language.

3.4 Common information transfer rules

Simplifying the transfer process in the multilingual machine translation is also able to result from the separation of the structure from the information. In the existing transfer-based machine translation systems the structural transfer has included the information transfer. It has brought out the duplication of the information and the increase of the memory space. But the isolation between the structure and the information results in excluding the shortcomings of the existing machine translation systems. In this sense, the common information transfer rules have the function to transfer the common information available to many languages, that is, they are the rules that copy the semantic informations from the source language to target language. The semantic informations are produced by the mapping from form to its meaning in the analysis. The following rules show the common information transfer rules: (We use the notation of the CAT2 system.) (2) Common information transfer rules

• Lexical_semantic_transfer =
  {head:{ehead:{sem:SEM}}}.[*] <=> {head:{ehead:{sem:SEM}}}.[*].
• Transfer_of_semantic_roles =
  {role:ROLE}.[*] <=> {role:ROLE}.[*].

The lexical semantic transfer says that the lexical semantic information of the source language is copied to that of the target language on the same node level and the reverse too ('<=>' means the bidirection). The transfer of semantic roles shows the copy of the information of the semantic role between the source language and the target language.

4.1 Korean analysis by parameterized common rules

According to the Korean standard word order the head word must always follow its argument or modifier. From this point of view we can select the head-final common rules for Korean under the multilingual common grammatical rules in the Figure 1. The head-final rules in Figure 1 and Head Feature Principle percolating the information of lexical head into that of its phrase are as follows: (the coordination structure of Korean can be considered as part of the 'Argument-Functional word structure'. I hold the coordination structure of Korean as the triple structure for the efficient analysis.)

Table 2. Parameterized common grammar rules for Korean
	head-final-structure	head-middle-structure
1	PRED => ARG PRED	COORD => ARG1 COORD ARG2
2	MODED => MOD MODED
3	FUNCT => ARG FUNCT

(4) Head_Feature_Principle = {head:HEAD}.[{},{head:HEAD}]. A Korean sentence that is analysed by the parameterized common grammar rules and the HFP results in what follows:
(5) cengpwunun saylowun kyeyhoykanul malyenhayessta. government+SUBJ new plan+OBJ make+PAST+DECL The government made a new plan. In (5) the fine line shows the application of 'FUNCT => ARG FUNCT', the dotted line that of 'MODED => MOD MODED' and the thick line that of 'PRED => ARG PRED'.

4.2 Korean analysis by grammatical constraint rules

With analysing Korean in the machine translation, we must consider specially the following [Oh 1994]:
(6) Korean Characteristics

• Phonological peculiarity
  sonyen-i, sonye-ka
  boy-SUBJ, girl-SUBJ
  boy, girl
• Double objects
  kunun seoulul yehayngul hayessta.
  He-SUBJ Seoul-OBJ trip-OBJ make-PAST-DECL
  He made a trip to Seoul
• Honorifics
  kyoswunimkkeyse osipnita.
  professor-SUBJ(HON) come-HON-DECL
  The professor comes.

These peculiarities of Korean can be explained by the constraint rules. The table 3 shows the relation between common rules and their constraint rules.

Table 3. Common rules and constraint rules
Korean characteristics	Common rules	Constraint rules
Phonological peculiarities	FUNCT => ARG FUNCT	Phonological rule
Double objects	PRED => ARG PRED	Argument exchange
Honorifics	HFP	Context information

- Phonological rule All morphemes contain their last phoneme that is subcategorized and predicted by a functional word. example) sonyen{phon:con} i{phon:voc,frame:{arg1:{phon:con}}} boy{phon:con} SUBJ{phon:voc,frame:{arg1:{phon:con}}} - Argument exchange The subcategorization structures of functional verb 'hata (= do/make)' and those of predicate noun are exchanged for each other in the lexicon:

Table 4. Lexicon of 'hata (do/make)'
lex	hata
	arg1	ARG1
	arg2	ARG2
frame		cat	noun
	arg3	frame	arg1	ARG1
			arg2	ARG2

example) kunun(arg1) seoulul(arg2) yehayngul(arg3(arg1,arg2)) ha(arg1,arg2,arg3)yessta. He-SUBJ Seoul-OBJ Trip-OBJ make-PAST-DECL He made a trip to Seoul. - Context information The context information of sentence subject agrees with that of verb phrase. example) kyoswunimkkeyse(context:honor) osi(context:honor)pnita. professor-SUBJ(HON) come-HON-DECL. The professor comes.

4.3 Transfer constraint rules

The syntactic tree of Korean results in the semantic tree through tree transformation. The semantic tree has the 'predicate-argument-modifier' arrangement. HFP also is applied to nodes of the semantic tree. We are transducing the Korean syntactic tree (5) to the following semantic tree through the transformation rules. (7) cengpwunun saylowun kyeyhoykanul malyenhayessta. government-SUBJ new plan-OBJ make-PAST-DECL. The government made a new plan. The semantic tree becomes the input of transfer. All semantic trees that can be transferred compositionally are transferred to target language by the 'common structural transfer rules' and 'common information tranfer rules'. There is, however, the compositional transfer that is not able to apply to the common information transfer rules. The idiomatic expressions with functional verbs 'hata(do/make)' or 'toyta(be done/be made)' belong to this example. We delete 'hata' during transformation from syntactic tree to semantic tree and copy the information of 'hata' to the feature 'functional verb' of predicate noun, so that the predicate of a sentence becomes the predicate noun during transformation from syntactic tree to semantic tree and copy the information of 'hata' to the feature 'functional verb' of predicate noun, so that the predicate of a sentence becomes the predicate noun. But there is no multilingual rule that can control the relation between the predicate noun of source language and the predicate noun of target language or between predicate noun of source language and verb or adjective of target language. For this reason we need the rule constraining the common transfer rule. Now we have the transfer constraint rules for the common information transfer rules. (8) Constraint rule of predicate noun

• idiomatic expression vs idiomatic expression
  
  Let copy the information of Korean functional verb to that of functional verb of target language, if the lexeme of target language has the functional verb that is equalent to the Korean idiomatic expression with 'hata'.
  
  ex.) sanpolul hata => take a walk, einen Sparziergang machen, sanpowo suru
  ilul hata => sikotowo suru
• idiomatic expression vs verb or adjective
  
  Let copy the information of Korean functional verb to that of the lexeme of target language, if the lexeme of target language has no functional verb that is equivalent to the Korean idiomatic expression with 'hata'.
  
  ex.) ilul hata => work, arbeiten