mirror of https://github.com/explosion/spaCy.git
88 lines
3.9 KiB
Python
88 lines
3.9 KiB
Python
from typing import Optional, List
|
|
from thinc.api import Model, chain, list2array, Linear, zero_init, use_ops
|
|
from thinc.types import Floats2d
|
|
|
|
from ...errors import Errors
|
|
from ...compat import Literal
|
|
from ...util import registry
|
|
from .._precomputable_affine import PrecomputableAffine
|
|
from ..tb_framework import TransitionModel
|
|
from ...tokens import Doc
|
|
|
|
|
|
@registry.architectures.register("spacy.TransitionBasedParser.v1")
|
|
def build_tb_parser_model(
|
|
tok2vec: Model[List[Doc], List[Floats2d]],
|
|
state_type: Literal["parser", "ner"],
|
|
extra_state_tokens: bool,
|
|
hidden_width: int,
|
|
maxout_pieces: int,
|
|
use_upper: bool = True,
|
|
nO: Optional[int] = None,
|
|
) -> Model:
|
|
"""
|
|
Build a transition-based parser model. Can apply to NER or dependency-parsing.
|
|
|
|
Transition-based parsing is an approach to structured prediction where the
|
|
task of predicting the structure is mapped to a series of state transitions.
|
|
You might find this tutorial helpful as background:
|
|
https://explosion.ai/blog/parsing-english-in-python
|
|
|
|
The neural network state prediction model consists of either two or three
|
|
subnetworks:
|
|
|
|
* tok2vec: Map each token into a vector representations. This subnetwork
|
|
is run once for each batch.
|
|
* lower: Construct a feature-specific vector for each (token, feature) pair.
|
|
This is also run once for each batch. Constructing the state
|
|
representation is then simply a matter of summing the component features
|
|
and applying the non-linearity.
|
|
* upper (optional): A feed-forward network that predicts scores from the
|
|
state representation. If not present, the output from the lower model is
|
|
used as action scores directly.
|
|
|
|
tok2vec (Model[List[Doc], List[Floats2d]]):
|
|
Subnetwork to map tokens into vector representations.
|
|
state_type (str):
|
|
String value denoting the type of parser model: "parser" or "ner"
|
|
extra_state_tokens (bool): Whether or not to use additional tokens in the context
|
|
to construct the state vector. Defaults to `False`, which means 3 and 8
|
|
for the NER and parser respectively. When set to `True`, this would become 6
|
|
feature sets (for the NER) or 13 (for the parser).
|
|
hidden_width (int): The width of the hidden layer.
|
|
maxout_pieces (int): How many pieces to use in the state prediction layer.
|
|
Recommended values are 1, 2 or 3. If 1, the maxout non-linearity
|
|
is replaced with a ReLu non-linearity if use_upper=True, and no
|
|
non-linearity if use_upper=False.
|
|
use_upper (bool): Whether to use an additional hidden layer after the state
|
|
vector in order to predict the action scores. It is recommended to set
|
|
this to False for large pretrained models such as transformers, and False
|
|
for smaller networks. The upper layer is computed on CPU, which becomes
|
|
a bottleneck on larger GPU-based models, where it's also less necessary.
|
|
nO (int or None): The number of actions the model will predict between.
|
|
Usually inferred from data at the beginning of training, or loaded from
|
|
disk.
|
|
"""
|
|
if state_type == "parser":
|
|
nr_feature_tokens = 13 if extra_state_tokens else 8
|
|
elif state_type == "ner":
|
|
nr_feature_tokens = 6 if extra_state_tokens else 3
|
|
else:
|
|
raise ValueError(Errors.E917.format(value=state_type))
|
|
t2v_width = tok2vec.get_dim("nO") if tok2vec.has_dim("nO") else None
|
|
tok2vec = chain(tok2vec, list2array(), Linear(hidden_width, t2v_width))
|
|
tok2vec.set_dim("nO", hidden_width)
|
|
lower = PrecomputableAffine(
|
|
nO=hidden_width if use_upper else nO,
|
|
nF=nr_feature_tokens,
|
|
nI=tok2vec.get_dim("nO"),
|
|
nP=maxout_pieces,
|
|
)
|
|
if use_upper:
|
|
with use_ops("numpy"):
|
|
# Initialize weights at zero, as it's a classification layer.
|
|
upper = Linear(nO=nO, init_W=zero_init)
|
|
else:
|
|
upper = None
|
|
return TransitionModel(tok2vec, lower, upper)
|