LexicalAnalysis

1.概述

　　Lexical Analysis of Chinese，简称 LAC，是一个联合的词法分析模型，在单个模型中完成中文分词、词性标注、专名识别任务。我们在自建的数据集上对分词、词性标注、专名识别进行整体的评估效果。主要通过标注来完成这些任务。

2.预测和损失函数

　　标注问题一般用crf来作为损失函数，然后用crf decoding来完成预测

　　其中crf decoding相当于viterbi算法

def lex_net(word, args, vocab_size, num_labels, for_infer=True, target=None):
    """
    define the lexical analysis network structure
    word: stores the input of the model
    for_infer: a boolean value, indicating if the model to be created is for training or predicting.

    return:
        for infer: return the prediction
        otherwise: return the prediction
    """
    word_emb_dim = args.word_emb_dim
    grnn_hidden_dim = args.grnn_hidden_dim
    emb_lr = args.emb_learning_rate if 'emb_learning_rate' in dir(args) else 1.0
    crf_lr = args.emb_learning_rate if 'crf_learning_rate' in dir(args) else 1.0
    bigru_num = args.bigru_num
    init_bound = 0.1
    IS_SPARSE = True

    def _bigru_layer(input_feature):
        """
        define the bidirectional gru layer
        """
        pre_gru = fluid.layers.fc(
            input=input_feature,
            size=grnn_hidden_dim * 3,
            param_attr=fluid.ParamAttr(
                initializer=fluid.initializer.Uniform(
                    low=-init_bound, high=init_bound),
                regularizer=fluid.regularizer.L2DecayRegularizer(
                    regularization_coeff=1e-4)))
        gru = fluid.layers.dynamic_gru(
            input=pre_gru,
            size=grnn_hidden_dim,
            param_attr=fluid.ParamAttr(
                initializer=fluid.initializer.Uniform(
                    low=-init_bound, high=init_bound),
                regularizer=fluid.regularizer.L2DecayRegularizer(
                    regularization_coeff=1e-4)))

        pre_gru_r = fluid.layers.fc(
            input=input_feature,
            size=grnn_hidden_dim * 3,
            param_attr=fluid.ParamAttr(
                initializer=fluid.initializer.Uniform(
                    low=-init_bound, high=init_bound),
                regularizer=fluid.regularizer.L2DecayRegularizer(
                    regularization_coeff=1e-4)))
        gru_r = fluid.layers.dynamic_gru(
            input=pre_gru_r,
            size=grnn_hidden_dim,
            is_reverse=True,
            param_attr=fluid.ParamAttr(
                initializer=fluid.initializer.Uniform(
                    low=-init_bound, high=init_bound),
                regularizer=fluid.regularizer.L2DecayRegularizer(
                    regularization_coeff=1e-4)))

        bi_merge = fluid.layers.concat(input=[gru, gru_r], axis=1)
        return bi_merge

    def _net_conf(word, target=None):
        """
        Configure the network
        """
        word_embedding = fluid.embedding(
            input=word,
            size=[vocab_size, word_emb_dim],
            dtype='float32',
            is_sparse=IS_SPARSE,
            param_attr=fluid.ParamAttr(
                learning_rate=emb_lr,
                name="word_emb",
                initializer=fluid.initializer.Uniform(
                    low=-init_bound, high=init_bound)))

        input_feature = word_embedding
        for i in range(bigru_num):
            bigru_output = _bigru_layer(input_feature)
            input_feature = bigru_output

        emission = fluid.layers.fc(
            size=num_labels,
            input=bigru_output,
            param_attr=fluid.ParamAttr(
                initializer=fluid.initializer.Uniform(
                    low=-init_bound, high=init_bound),
                regularizer=fluid.regularizer.L2DecayRegularizer(
                    regularization_coeff=1e-4)))

        if target is not None:
            crf_cost = fluid.layers.linear_chain_crf(
                input=emission,
                label=target,
                param_attr=fluid.ParamAttr(
                    name='crfw', learning_rate=crf_lr))
            avg_cost = fluid.layers.mean(x=crf_cost)
            crf_decode = fluid.layers.crf_decoding(
                input=emission, param_attr=fluid.ParamAttr(name='crfw'))
            return avg_cost, crf_decode

        else:
            size = emission.shape[1]
            fluid.layers.create_parameter(
                shape=[size + 2, size], dtype=emission.dtype, name='crfw')
            crf_decode = fluid.layers.crf_decoding(
                input=emission, param_attr=fluid.ParamAttr(name='crfw'))

        return crf_decode

    if for_infer:
        return _net_conf(word)

    else:
        # assert target != None, "target is necessary for training"
        return _net_conf(word, target)

3.lod_level

　　fluid.data参数中的lod_level指的是传入数据lod的个数如果为1表示一个batch为 二维的，如果为二表示一个batch是三维的。