Nominal Measurement Phrases: Syntax Analysis And Dependencies

Nominal measurement phrases, especially those involving prepositional phrases (PP) like "5 days after the election," present intriguing challenges in syntactic analysis. This article delves into the complexities of these phrases, focusing on two primary issues: headedness and dependency relations (deprel). We will explore how different treebanks treat these constructions, highlighting inconsistencies and discussing potential solutions for a more unified approach.

The Core Issues: Headedness and Dependency Relations

When analyzing nominal measurement phrases with PPs, the first crucial decision involves determining the head of the phrase. In simpler terms, which word or phrase is the most important, and which words modify it? Secondly, we must establish the correct dependency relation between the measurement phrase and the element it modifies within the sentence. Should it be treated as a general modifier (nmod), an oblique argument (obl), or something else entirely? These choices impact the overall structure of the parse tree and influence how we understand the grammatical relationships within the sentence.

These decisions regarding headedness and dependency can significantly influence the interpretation and processing of sentences. Different approaches can lead to varied syntactic structures, impacting how computational systems and linguists alike understand the relationships between words. This article aims to clarify these issues by examining current practices in different treebanks and proposing a more consistent framework for future annotations. Proper handling of these phrases is crucial for accurate natural language processing and a deeper understanding of syntactic structures.

Measurement Phrase as Head: A Closer Look

One approach treats the measurement phrase itself as the head, with the rest of the construction modifying it. In this model, the PP often attaches as a nmod (nominal modifier).

The nmod approach, exemplified by the Czech-PDTC treebank, positions the measurement phrase as the central element. This perspective suggests that the temporal aspect (e.g., "5 days") is the core, with the subsequent prepositional phrase ("after the election") providing further specification. In the Czech-PDTC convention, phrases like “three days after his inauguration” are structured in this manner, emphasizing the temporal duration as the head.

However, a critical question arises: what is the rationale behind elevating the measurement phrase to the head position? Is there a linguistic justification for prioritizing the temporal duration over the event or entity being modified? A key consideration is the optionality of the PP. If the PP can be omitted without significantly altering the core meaning of the sentence, it might suggest that the measurement phrase is indeed the head. For instance, "5 days" might stand alone, but "after the election" typically requires a temporal reference point. However, this approach is not universally adopted, leading to inconsistencies across different linguistic analyses.

Measurement Phrase as Modifier: Diverse Approaches

Alternatively, the measurement phrase can be analyzed as a modifier, with the nominal element being modified as the head. This approach is prevalent in several treebanks, including those for English, Swedish, and French, but the specific deprel used varies.

nmod

In some treebanks, like French-Sequoia, the measurement phrase is attached as a generic nmod. This indicates that the phrase modifies the noun, providing additional information about it. This approach aligns with the general function of a nominal modifier, which adds descriptive or limiting details to a noun. For example, in the phrase “three days after the inauguration,” the phrase “after the inauguration” provides temporal context, modifying the duration indicated by “three days.”

nmod:unmarked

The English Web Treebank (EWT) adopts a more specific approach, using nmod:unmarked. This sub-type of nmod suggests a less prominent or default form of nominal modification, often used when the relationship is clear and does not require further specification. The :unmarked convention is particularly common in English, where the syntactic structure often relies on word order and implicit relationships. This usage indicates that the temporal phrase is a standard modifier without needing further elaboration on its role.

obl and obl:unmarked

Other treebanks, such as Swedish-Talbanken and English-GUM, employ obl (oblique argument) or obl:unmarked. An oblique argument typically represents a non-core argument of a verb or noun, often involving prepositional phrases that provide circumstantial information. The distinction between obl and nmod hinges on the perceived importance and integration of the modifying phrase. If the temporal phrase is considered crucial to the meaning and acts more like an argument, obl is preferred. The :unmarked variant suggests a standard, less emphasized form of oblique modification.

For example, in the Swedish-Talbanken, the temporal phrase might be seen as an essential component specifying when an event occurred, thus justifying its treatment as an oblique argument. In English-GUM, obl:unmarked reflects a similar understanding, though with a less emphasized role compared to core arguments.

The variation between nmod and obl raises a critical question: which dependency relation best captures the syntactic function of measurement phrases? While nmod indicates a general modification, obl suggests a more integral, argument-like role. This decision impacts how the phrase is interpreted within the broader sentence structure. The :unmarked convention adds another layer, suggesting a default or less prominent type of modification.

The English-Specific :unmarked Convention

The :unmarked convention appears to be somewhat specific to English. It is used to denote a default or less prominent form of a dependency relation. While this can be useful in capturing nuances within English syntax, it might not translate well to other languages. This raises concerns about cross-linguistic consistency and the generalizability of syntactic annotations.

The English-specific nature of :unmarked highlights a broader challenge in universal dependencies: balancing language-specific features with the goal of creating a universal framework. Over-reliance on language-specific conventions can undermine the consistency and comparability of annotations across different languages. Therefore, careful consideration is needed when applying such conventions to ensure they enhance rather than detract from the universality of the dependency scheme.

Navigating the nmod vs. obl Dilemma

The central question remains: which is better, nmod or obl? This choice is not arbitrary; it reflects a fundamental decision about the syntactic role of the measurement phrase. The nmod relation suggests a general modification, akin to an adjective modifying a noun. On the other hand, obl implies a more integral, argument-like role, similar to a prepositional phrase acting as an adverbial modifier.

To decide between nmod and obl, we must consider the semantic contribution of the measurement phrase. Does it merely provide additional information, or is it essential to the meaning of the clause? If the temporal phrase is crucial for understanding the timing or duration of the event, obl might be more appropriate. However, if it simply adds context, nmod could suffice. This distinction requires careful semantic analysis and a consistent application of dependency guidelines.

Related Constructions: Subordinate Clauses

An additional layer of complexity arises when the second part of the construction is a subordinate clause, as in "5 days after the election took place." In such cases, the consensus seems to lean towards treating the measurement phrase as obl:unmarked if "5 days" is considered a modifier. This aligns with the understanding that the temporal phrase provides circumstantial information about the event described in the subordinate clause.

When a subordinate clause is involved, the temporal phrase often acts as an adverbial modifier, specifying the timing of the event described in the clause. This function aligns well with the obl relation, which is used for non-core arguments and adverbial modifiers. The :unmarked convention further suggests that this is a standard way of expressing temporal modification in English. However, consistency in applying this convention is crucial for maintaining a coherent syntactic analysis.

Towards a More Consistent Approach

In conclusion, the analysis of nominal measurement phrases with PPs reveals a landscape of varied approaches and unresolved questions. While different treebanks offer valuable insights, the inconsistencies in headedness and dependency relations highlight the need for a more unified framework. A deeper consideration of the semantic contribution of the measurement phrase, along with a careful balance between language-specific conventions and universal principles, is essential for achieving this goal.

Future research should focus on developing clear guidelines that address these issues, promoting greater consistency across treebanks and languages. This will not only enhance the accuracy of syntactic analyses but also facilitate cross-linguistic comparisons and improve the performance of natural language processing systems.

For further reading on Universal Dependencies and syntactic annotation, visit the Universal Dependencies website.

By striving for consistency and clarity in our syntactic analyses, we can build a more robust foundation for understanding the intricate structures of human language.