Subsections

• Introduction
• Main organization of prepositions
• Prepositions and Semantic Relations for Modifiers
• Relations with other areas of lexical semantics
• Prepositions in LKB
• Prepositions in Applications

   
Prepositions

   
Introduction

Prepositions have not been much studied in traditional lexical semantics [Zel93], [Tru92], [VanD94], [Lin97] compared to the large amount of work devoted to verbs and to nouns. They nevertheless play a very important role in semantics and have many connections with most of the other syntactic categories. They have been, however, extensively studied in psycho-linguistics, in particular spatial prepositions.

   
Main organization of prepositions

Prepositions occur in the following three main syntactic situations:

• as heads of prepositional phrases,
• as an element in verbal compounds (e.g. turn out, give up, aufsteigen, anrufen, etc. or a more complex form as: sich fressen gegenseitig auf), where they largely contribute to the semantics of the expression. This compound is subject to various more or less strong constraints, in particular in Germanic languages,
• some prepositions function s case markers as in: donner qqchose à Marie where [ à Marie] can possibly be analysed not as a PP but as an NP[prep=a] or a NP[case=dative].

• as a `connector' in nominal compounds (planche à voile, plancha a vela, plan de vuelo) (REF),
• as introducing small clauses in a number of languages,
• preposition may be incorporated [Bak88] (to climb (up) versus to climb down, where down is obligatory whereas up may be incorporated into the verb).

When dealing with prepositions, a clear distinction appears between semantically full and semantically empty prepositions.

• Semantically empty prepositions are prepositions which are strongly bound by a predicative head, like on, in the example: John relies on his father where on cannot be substituted by a semantically close preposition like in or over. They are considered to be case markers by some approaches (as suggested by [Pol87] and developped by [Bad96]). These prepositions are lexically predicted by the predicative head and, therefore, do not contribute to the semantics of the sentence. In a Machine Translation system like EUROTRA 3.9.1, they are featurised (o elevated) in the process of parsing : that is, they disappear as lexical nodes and their lexical value is encoded as an attribute of the predicative head. This implies that they are not translated, ut are generated in the target language from the information encoded in the entry of the predicative head.
• Full prepositions, on the contrary, are heads of prepositional phrases (see2.9.2) . They always subcategorize for (only) one argument, which in most cases is an NP, but can also be a finite or no inite clause, an adverb or even a PP. Full prepositional phrases may function as :
  • adjuncts (weakly bound by a predicative governor), like on, in: The book lies on the table where on can be substituted by a semantically close preposition, because the predicate demands a locative complement and not a specific preposition.
  • or modifiers (like for, in : John works for his father where the prepositional phrase is not particularly predicted by the verb, and the semantics it conveys (benefactive) may apply to other verbs as well: John (dances /bakes a cake / fixes the TV set) for his father

Let us now examine a simple semantic classification for prepositions. Note first that prepositions are highly polysemous; they are also subject to many metaphorical extensions, for example spatial preopositions have for most of them a metaphorical extension to abstract entities, viewed as locations (e.g. against a wall $\rightarrow$ against some principles). We can however tentatively propose the following general classification, where some items may overlapp on different ontological domains (e.g. time and space):

• temporal prepositions:
  • expressing anteriority (before, until),
  • expressing duration (durant, pendant, while),
  • expressing posteriority (after, despuès, as soon as).
• spatial prepositions:
  • expressing source (from, à partir de, depuis, since),
  • expressing position, either absolute (en, chez) or relative (under, in, infront of),
  • goal, reached, (à),
  • direction, not necessarily reached (via, toward, to, vers, hasta).
• prepositions expressing cause (because of, lors de, par, suite à),
• prepositions expressing consequences (in order to, de façon à),
• prepositions expressing goals or purpose (for, with the intention of, afin de),
• prepositions expressing conditions (à condition de),
• prepositions expressing means or manner:
  • manner (en selon),
  • accompaniement (with),
  • instrumental means (avec, by means of par).

Prepositions across languages

The use of prepositions can, in general, be specified quite unambiguously. For example, for an event occuring after a certain date, the prepositions after, nach(dem), na(dat) après, despuès will be respectively used for English, German, Dutch, French and Spanish, if the action takes place before the date, then we respectively have before, (be)vor, voor(dat), avant, antes.

Prepositions do not have often direct correspondences across languages. For example if S is an event, we have the following preposition lexicalizations depending on the duration and the type of event:

1.

simple point: at, bei, bij, à (English, German, Dutch, French),

2.

S has a duration, and happened once in the past: when/as, als, toen, lors de; als becomes wie in case of present tense in German,

3.

otherwise: when/as, wenn, als/wanneer, lors de.

¿From a different perspective around translates in German as gegen, um, at translates as um, zu, bei, an, in and by, until translate as bis.

Similarly, verbs may select very different types of prepositions in two different languages:
dream about someone,
réver de/à quelqu'un,
soñar con alguien. (Spanish: to dream with someone)
Whereas about and de have about equivalent meanings, con is completely different. There are many divergences of this type which make machine translation quite difficult.

In the context of a multilingual system, the need for assigning some sort of semantics to modifying prepositional phrases may be illustrated by these two facts

• structural disambiguation : i.e. ambiguous PP attachment, as on in: John read the report on new technologies where on may be attached to the verb read or to the noun report.
• lexical selection of the target preposition in transfer :

  
   
  
                    Italian                     Spanish
  
             per (benefactive)     =>              para
  
             per (cause)           =>              por
  
  

Italian per incorporates both the meanings of Spanish para and por: without any kind of semantic information it is not possible to decide which translation must be chosen, as may be seen in the following examples. The first set corresponds to benefactive per and the second to causative per:
1. Ha scritto una lettera per la sua fidanzata
Ha escrito una carta para su novia
(He) has written a letter for her girlfriend
2. Ha scritto una lettera per paura
Ha escrito una carta por miedo
(He) has written a letter out of fear.

   
Prepositions and Semantic Relations for Modifiers

The work reported here has mainly been developed within Eurotra, 3.9.1.

Semantic Relations for Modifiers : MODSR An experiment on Semantic Relations for Modifiers was carried out in the context of the Eurotra project by some language groups during 1989 and was afterwards adopted as legislation by the rest of the groups.

>From the examples above, it seems clear that a mere lexical typification of the preposition (like benefactive or causative) is not sufficient to perform the disambiguation, due to the polysemous nature of most prepositions. A calculation of the semantic value ( or relation ) of the whole prepositional phrase is needed. Thus, the semantic relation (or modsr value) of a PP of the form: P + NP has to be calculated on the basis of the lexical value of the preposition P combined with the lexical semantic value of the NP. Thus, for instance, the preposition with may have several semantic values, depending on the NP that follows it:

 

        PP[ with + NP (sem=hum)] =>  PP[modsr=accompaniment]                

        

        PP[ with + NP (sem=non-hum)] => PP[modsr=instrument]

It appears that some set of lexical semantic features (LSF) for nouns is needed, but since the process of calculation is internal to each language module, each of them is free to use its own set, which may have different degrees of granularity. On the other hand, the set of modsr labels belongs to the Eurotra Interface Structure (IS) and thus is shared by all languages. Here follows the list of modsr values that was agreed upon. They are divided into two big groups :

• those that apply to PPs modifying predicative heads (verbs and predicative nouns)
• those that apply to PPs modifying nonpredicative heads (nonpredicative nouns)

This distinction is justified because, from a semantic point of view, the relation between the modifier and the head is of a different type in both cases, as sustained by [Pol87]. Also , from a syntactic point of view, the choice of the preposition for modifiers of nominal heads is much more restricted, especially in the Romance languages where the most frequent is of (e in French, Spanish, Portuguese and Catalan, and di in Italian). We could say that nonpredicative (or nominal) prepositional modifiers behave like adjectives while predicative prepositional modifiers behave like adverbs. Predicative nouns are a bit special because they combine a verbal and a nominal nature.

• Modifiers of predicative heads:

  1.

  Place-position : 'The report is ON THE TABLE'. It is further subdivided in positioninon

  2.

  Place-goal : 'The boy is looking TOWARDS THE BEACH'

  3.

  Place-origin : 'FROM THIS WINDOW, the views are magnificent'

  4.

  Place-path : 'He ran THROUGH THE FIELDS'

  5.

  Cause : 'He died BECAUSE OF THE COLD'

  6.

  Aim : 'He did it TO SAVE HIMSELF'

  7.

  Concern : 'She told me ABOUT HER FRIEND'

  8.

  Accompaniment : 'The soldiers came WITH THEIR GIRLFRIENDS'

  9.

  Instrument : 'They bombed Baghdad WITH MISSILES'

  10.

  Benefactive : 'He turned on the heater FOR LINDA'

  11.

  Substitute : 'He appeared on the news, speaking FOR THE STATE DEPARTMENT'

  12.

  Manner : 'The government reacted WITH CAUTION'

  13.

  Function : 'I tell you this AS A FRIEND'

  14.

  Measure :'Fabrics are sold BY THE METRE'

  15.

  Comparison : 'Columbia was a young city COMPARED TO VENERABLE CHARLESTON'

  16.

  Time : 'He only sees her AT CHRISTMAS AND EASTERN'

• Modifiers of non-predicative heads :

  1.

  Quality-place : it may be further subdivided in :

  (a)

  place = position: 'a brick IN THE WALL'

  (b)

  place = goal : 'the train TO LONDON'

  (c)

  place = origin :'oranges FROM SPAIN'

  (d)

  place = path : 'a road THROUGH THE DESERT'

  2.

  Quality-whole : 'the other side OF THE SQUARE'

  3.

  Quality-stuff : 'loose-fitting garments OF LINEN'

  4.

  Quality-quality : it may be further subdivided in:

  (a)

  quality = inherent : 'a car WITH FIVE DOORS'

  (b)

  quality = state: 'a car WITH A BROKEN GLASS'

  5.

  Quality-concern : 'a report ON THE IMPLEMENTATION'

  6.

  Quality-aim : 'a room FOR RENT'

  7.

  Quality-specification : 'the island OF CUBA'

  8.

  Quality-function : 'Clinton, AS PRESIDENT OF THE US'

  9.

  Quality-measure : 'a project OF SEVERAL MILLIONS'

   
Relations with other areas of lexical semantics

The relations that prepositions have with other elements of lexical semantics are the following:

• Prepositions head prepositional phrases, as such they impose selectional restrictions, e.g. a spatial proposition expects an NP of type location. Prepositions can then be associated with a kind of subcategorization frame.
• Prepositions assign thematic roles to the NP they head, they can therefore be associated with a thematic grid, similarly to verbs.
• We may also consider that they assign a thematic role to other NPs involved in the relation described by the preposition.
• Prepositions play an important role in the definition of verb syntactic alternations 2.6.2, e.g. the into/onto, on/with and conative alternations [Lev93].
• Preposition play a crucial role for identifying the semantics of modifiers, in particular they indicate means, manner, purpose, time, location, accompaniement and amount 2.6.2.

   
Prepositions in LKB

Prepositions being a closed set of words are usaully described in depth in most lexical knowledge bases. They can be grouped into families as suggested above in 2.9.1. They usually share a number of properties, but are not in general included into major taxonomies.

   
Prepositions in Applications

As already shown above, prepositions may be quite difficult to translate in MT applications 4.1, and at that level, lexical semantics is of much use to help disambiguate and select the right prepositions 3.9, 3.10, 3.7 5.3.

Another important role of prepositions is to contribute to solving ambiguities in PP-attachment. This is also a complex task, but the semantics of prepositions can be used to decide whether the PP is a verb complement (argument or modifier) or a noun complement.

Finally, prepositions convey a quite important semantic load, in spite of their high polysemic nature. They are in particular important to identify the semantics of modifiers. From that point of view, they are of much use in information retrieval systems for the extraction on information 4.3, 4.2 in modifiers (e.g. when predicate-argument structures are used, possibly combined with thematic roles identifying the roles of NPs or PPs).