Meaning Representation of E nglish Prepositional Phrase Roles: SNACS Supersenses vs. Tectogrammatical Functors (2023)

Abstract: This work compares two ways of annotating semantic relations expressed in prepositional phrases: semantic classes in the Semantic Network of Adposition and Case Supersenses (SNACS), and tectogrammatical functors from the Prague English Dependency Treebank (PEDT). We compare the label definitions in the respective annotation guidelines to determine expected mappings, then check how well these work empirically using Wall Street Journal text. In the definitions we find substantial overlap in the distributions of the two schemata with respect to participants and circumstantials, but substantial divergence for configurational relationships between nominals. This is borne out by the empirical analysis. Examining the data more closely for participants and circumstantials reveals that there are some unexpected, yet systematic divergences between definitionally aligned groups.

## introduction broad coverage descriptive frameworks for annotating lexical semantics have proven useful for researchers in the field of computational semantics. most of these frameworks have a primary focus on verbs and their participants @xcite @xcite , though some frameworks extend annotation schema to cover the arguments of nominal phrases @xcite . relatively few frameworks have focused on comprehensive accounts of prepositions, which can modify both verbal and nominal heads @xcite , and can contribute crucial semantic information to sentences despite often being thought of as purely functional elements. the most recent and comprehensive attempt to cover the semantics of prepositions is the semantic network of adposition and case supersenses, or snacs @xcite @xcite , which is a hierarchy of semantic classifications of prepositional modifiers. snacs contains 52 total preposition semantic classes, or supersenses, which are arranged into a hierarchy with different levels of granularity at each point in the hierarchy. in english, the snacs framework has been applied to the reviews section of the english web treebank (ewt) corpus @xcite , resulting in the streusle corpus with gold snacs annotations @xcite . for researchers interested in the lexical semantics of prepositions, the streusle corpus is a valuable resource, but is smaller in size compared to corpora that have been annotated for other lexical semantic projects. while some of these other resources do mark some semantic information conveyed by prepositional phrases, it is an open question to what extent these more general semantic frameworks overlap with the preposition-centric hierarchy of snacs. if there is significant overlap between corresponding classes across different annotation schema, it may be possible to convert the classifications of prepositional phrases in these more general schemata into corresponding snacs supersenses. this would make it possible to quickly augment the available data annotated within the snacs hierarchy, and would provide useful comparisons between the coverage of different annotation schemata. in particular, this research highlights the prague english dependency treebank (pedt, @xcite as one resource with potential overlap with snacs. 1,2 the pedt contains multiple layers of 1 pedt is the english side of the prague czech-english dependency treebank. one reason to examine this framework and corpus is that if the correspondence proves reliable for english, it might be leveraged to obtain heuristic snacs annotations of czech data as well, since the tectogrammatical annotation scheme is also applied in the czech translation of the wall street journal corpus. ## definitional comparison the snacs hierarchy v2.6 @xcite contains 52 total supersenses organized into 3 main branches: the circumstance branch, the participant branch, and the configuration branch. recent versions of the snacs hierarchy assign supersenses to a preposition for both its scene role and its function role. the scene role represents the contextual semantic role of a preposition in combination with the predicate, while the function role is more faithful to the lexical semantics of the preposition @xcite . in many instances, the two roles are the same, but in cases where the scene and function roles differ, the two are represented using the scene↝function notation. we hypothesize that the scene role snacs supersenses will more closely align with pedt functors, and thus focus on scene role supersenses unless otherwise specified. many snacs supersenses correspond more or less directly to pedt functors based upon the definitions set forth in their respective guidelines. we see in on the other hand, snacs direction is used to express the orientation of motion where the end result is not specified. we can observe the distinction in examples (4) and ( 5 ), which are taken from the most recent version of the snacs annotation guidelines @xcite . if dir1 and dir3 do not generally correspond to direction, then direction is exceptional in that it does not have a directly corresponding pedt functor. di-rection, which is a subtype of path, is probably most closely related to the more general dir2. participant supersenses, which introduce more canonical participants to events, also often correspond well to pedt functors. the instru-ment supersense lacks a directly corresponding functor, but is grouped with the means supersense under the scope of the means functor. the acmp functor at least sometimes corresponds to ancillary, as shown in example (6). the act and pat functors are potentially problematic, since they mark primarily syntactic roles of arguments, not semantic roles. this means that finer-grained supersenses, such as experiencer and stimu-lus, are not captured by pedt functors. furthermore, cost is perhaps the most problematic of the participant supersenses, with ext being a marginal match at best. configuration supersenses, which describe state or property relationships between two nominals, are the least similar to pedt functors, though there are some clear correspondences shown in corresponding pedt functors. there are also some pedt functors which are beyond the scope of the snacs hierarchy: for instance, functors which mark paratactic relations (e.g. contra), express primarily discourse functions (e.g. att), or mark types of syntactic information which is not conveyed in prepositional phrases (e.g. apps). these functors are omitted from further analysis. ## conclusion in this work, we compare snacs supersenses with pedt tectogrammatical functors in terms of how they account for english prepositions. we show that the substantial definitional overlap between snacs supersenses and pedt functors is reflected in the overlapping distributions of the various semantic classes, particularly for spatial, temporal, and participant related supersenses, with less overlap on the configuration branch. however, we also find substantial divergences between the two schemata, due in part to limitations of the automatic snacs classifier we employed. we observe that a simple heuristic mapping from pedt functors to snacs supersenses aligns somewhat with classifier predictions, but also has substantial limitations due to the differences between the two frameworks.