spaCy/spacy/ml/models/parser.py

176 lines
6.7 KiB
Python

from typing import List, Optional, cast
from thinc.api import Linear, Model, chain, list2array, use_ops, zero_init
from thinc.types import Floats2d
from ...compat import Literal
from ...errors import Errors
from ...tokens import Doc
from ...util import registry
from .._precomputable_affine import PrecomputableAffine
from ..tb_framework import TransitionModel
@registry.architectures("spacy.TransitionBasedParser.v2")
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,
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 True
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 = _define_lower(
nO=hidden_width if use_upper else nO,
nF=nr_feature_tokens,
nI=tok2vec.get_dim("nO"),
nP=maxout_pieces,
)
upper = None
if use_upper:
with use_ops("cpu"):
# Initialize weights at zero, as it's a classification layer.
upper = _define_upper(nO=nO, nI=None)
return TransitionModel(tok2vec, lower, upper, resize_output)
def _define_upper(nO, nI):
return Linear(nO=nO, nI=nI, init_W=zero_init)
def _define_lower(nO, nF, nI, nP):
return PrecomputableAffine(nO=nO, nF=nF, nI=nI, nP=nP)
def resize_output(model, new_nO):
if model.attrs["has_upper"]:
return _resize_upper(model, new_nO)
return _resize_lower(model, new_nO)
def _resize_upper(model, new_nO):
upper = model.get_ref("upper")
if upper.has_dim("nO") is None:
upper.set_dim("nO", new_nO)
return model
elif new_nO == upper.get_dim("nO"):
return model
smaller = upper
nI = smaller.maybe_get_dim("nI")
with use_ops("cpu"):
larger = _define_upper(nO=new_nO, nI=nI)
# it could be that the model is not initialized yet, then skip this bit
if smaller.has_param("W"):
larger_W = larger.ops.alloc2f(new_nO, nI)
larger_b = larger.ops.alloc1f(new_nO)
smaller_W = smaller.get_param("W")
smaller_b = smaller.get_param("b")
# Weights are stored in (nr_out, nr_in) format, so we're basically
# just adding rows here.
if smaller.has_dim("nO"):
old_nO = smaller.get_dim("nO")
larger_W[:old_nO] = smaller_W
larger_b[:old_nO] = smaller_b
for i in range(old_nO, new_nO):
model.attrs["unseen_classes"].add(i)
larger.set_param("W", larger_W)
larger.set_param("b", larger_b)
model._layers[-1] = larger
model.set_ref("upper", larger)
return model
def _resize_lower(model, new_nO):
lower = model.get_ref("lower")
if lower.has_dim("nO") is None:
lower.set_dim("nO", new_nO)
return model
smaller = lower
nI = smaller.maybe_get_dim("nI")
nF = smaller.maybe_get_dim("nF")
nP = smaller.maybe_get_dim("nP")
larger = _define_lower(nO=new_nO, nI=nI, nF=nF, nP=nP)
# it could be that the model is not initialized yet, then skip this bit
if smaller.has_param("W"):
larger_W = larger.ops.alloc4f(nF, new_nO, nP, nI)
larger_b = larger.ops.alloc2f(new_nO, nP)
larger_pad = larger.ops.alloc4f(1, nF, new_nO, nP)
smaller_W = smaller.get_param("W")
smaller_b = smaller.get_param("b")
smaller_pad = smaller.get_param("pad")
# Copy the old weights and padding into the new layer
if smaller.has_dim("nO"):
old_nO = smaller.get_dim("nO")
larger_W[:, 0:old_nO, :, :] = smaller_W
larger_pad[:, :, 0:old_nO, :] = smaller_pad
larger_b[0:old_nO, :] = smaller_b
for i in range(old_nO, new_nO):
model.attrs["unseen_classes"].add(i)
larger.set_param("W", larger_W)
larger.set_param("b", larger_b)
larger.set_param("pad", larger_pad)
model._layers[1] = larger
model.set_ref("lower", larger)
return model