Introduction to the CoNLL-2005 Shared Task: Semantic Role Labeling
What it is about
The overview of the 2005 shared task on SRL over PropBank. Systems label the arguments of given target verbs with roles. The training data is the Wall Street Journal sections 02 to 21 with full syntactic parses from two parsers, and the test is section 23 plus three Brown sections (ck01 to 03) to test robustness across corpora. Nineteen systems took part, all in the closed setting. The best system reached F1 79.44 on the WSJ test. Every system lost about 10 F1 points on the Brown set, which the authors attribute to parser error propagation in the pipeline. The top four systems were combinations of several systems working on different parses, and the best single system reached 75.04 on the combined test. A seven-rule baseline (for example, the noun phrase before the verb is A0, the one after is A1) is far below all systems. The argument is strict: a span is right only if its boundaries and its label are both right, and the verb itself is not scored.
Ideas
- I1. Cross-corpus gate: evaluate Mova's rule-based role labeller on a second genre, such as the school books against other text, and report the drop. The paper's 10-point drop for every system is a useful expectation, and a claim of generality should show it.
- I2. Implement the seven-rule baseline in
prag/src/roles.rsas Mova's first-tier fallback and as the floor of every role measure. It is a deterministic rule set, so it is easy to audit. - I3. Parse combination: take the agreed trees from
tools/treeagreeand count role votes over several parsers, as the top systems did. Measure the gain over the best single parser on school sentences. - I4. Adopt the strict scoring (span and label both correct, verb excluded) in the role evaluation of
prag, so that Mova's numbers are comparable to published ones.
For Mova
The chapters are languages/en/21-clause-structure.md and languages/en/13-verbs.md. The code is prag/src/roles.rs and tools/treeagree. The measure is span-and-label F1 on school sentences, run twice to check determinism, and the cross-genre gate in I1.
Library summary
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "CC BY-NC-SA 3.0 (ACL Anthology, before 2016)" does not allow redistributing the text itself. Original — aclanthology.org/W05-0620.pdf
Summary
This paper describes the CoNLL-2005 competition, whose shared task was devoted to Semantic Role Labeling (SRL). For each target verb in an English sentence, a system must find the phrases that fill its semantic roles and label them with PropBank roles. The 2004 edition gave systems only partial syntax. This edition added three things: full parse trees from two alternative parsers, a much larger training set from the WSJ part of the Penn TreeBank annotated with PropBank, and an extra out-of-domain test set from the Brown corpus.
Systems are scored by precision, recall and F1 over whole arguments. An argument counts only if both its span and its label are correct.
Nineteen teams took part, all in the closed challenge. The strongest system, Punyakanok et al. (2005), reached F1 79.44 on the WSJ test set, roughly 10 points above the best 2004 result. On Brown, every system lost about 10 F1 points. The authors present this as evidence that errors pile up through pipelined NLP architectures when the domain changes.
Key points
- Data splits: training uses WSJ sections 02-21, development uses section 24, and the WSJ test uses section 23. Brown sections ck01-03 provide the cross-corpus test. The training portion has 39,832 sentences, 950,028 tokens, 90,750 propositions and 239,858 arguments.
- Input annotations: words, PoS tags, base chunks, clauses, named entities, and full syntactic trees from two parsers. Role labels come from PropBank-1.0. They cover numbered arguments (A0–A5, AA), 13 adjunct types (AM-), references (R-) and the verb (V).
- Results:
- The best individual system (Surdeanu and Turmo, 2005) got F1 75.04 on the combined WSJ+Brown test, about 3 points below the best combined system.
- With the same architecture, Màrquez et al. (2005) scored 73.57 on development using partial parsing, versus 75.75 using full parsing.
- Effect of each test set: most systems scored 1–2 F1 points higher on the WSJ test than on development. On Brown they dropped about 10 points, even though the Brown baseline was higher.
- Scoring tool: the official scorer is srl-eval.pl. Data, software and system outputs were published on the task website.
Interesting ideas
- Drop trivial items from the metric. The verb argument is excluded from scoring because it is almost always given by the target verb, and counting it would inflate the scores. Any benchmark can apply this: remove near-free items so the metric reflects the hard part of the task.
- Separate closed and open tracks. A closed track lets only the training data and the organizers' preprocessors be used, while an open track allows external resources. The closed track makes systems directly comparable, and the open track measures what extra knowledge adds.
- Test on a second domain. Adding an out-of-domain test set (Brown next to WSJ) exposed a roughly 10-point drop that in-domain testing would have hidden. Testing on a different source is a cheap way to check robustness, for example for low-resource languages with mixed-genre data.
- Combine systems built on different parses. The top systems merged several SRL outputs, each built on different syntactic analyses. This makes up for any single parse being wrong and improves both coverage and robustness.
- Give everyone the same predicted inputs. The organizers supplied the outputs of the syntactic preprocessors, including several alternative parsers. This makes it possible to measure how much each layer of syntax helps, and it keeps comparisons fair.
Cite
@inproceedings{carreras2005introduction,
title = {{Introduction to the CoNLL-2005 Shared Task: Semantic Role Labeling}},
author = {Carreras, Xavier and Màrquez, Lluís},
booktitle = {Proceedings of the Ninth Conference on Computational Natural Language Learning (CoNLL-2005)},
year = {2005},
doi = {10.3115/1706543.1706571},
url = {https://doi.org/10.3115/1706543.1706571}
}References
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