subtitles/zh-CN/13_word-based-tokenizers.srt

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- 让我们来看看基于单词的分词。
*[译者注: token, tokenization, tokenizer 等词均译成了 分词*, 实则不翻译最佳]
- Let's take a look at word-based tokenization.

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基于单词的分词化的想法是
Word-based tokenization is the idea

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将原始文本拆分成单词
of splitting the raw text into words

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通过按空格或其他特定规则拆分，
by splitting on spaces or other specific rules,

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比如标点符号。
like punctuation.

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在这个算法中，每个单词都有一个特定的数字
In this algorithm, each word has a specific number

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或者说他的 ID。
or ID attributed to it.

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在这里，"let's" 的 ID 是 250，
Here, let's has the ID 250,

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 "do" 是 861，并且分词化
do has 861, and tokenization

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后面跟感叹号的是 345。
followed by an exclamation mark has 345.

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这个方法很有趣
This approach is interesting

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因为模型有表示
as the model has representations

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是基于整个单词的。
that are based on entire words.

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单个号码所持有的信息量高，
The information held in a single number is high,

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因为一个词包含很多上下文
as a word contains a lot of contextual

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和语义信息。
and semantic information.

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然而，这种方法确实有其局限性。
However, this approach does have its limits.

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比如 dog 这个词和 dogs 这个词很相似
For example, the word dog and the word dogs are very similar

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他们的意思很接近。
and their meaning is close.

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然而，基于单词的分词化，
The word-based tokenization, however,

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会给这两个词赋予完全不同的 ID
will attribute entirely different IDs to these two words

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因此模型将学习
and the model will therefore learn

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这两个词的两个不同的嵌入。
two different embeddings for these two words.

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这很不幸，因为我们想要这个模型
This is unfortunate as we would like the model

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理解这些词是确实相关的，
to understand that these words are indeed related,

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而 dogs 只是 dog 这个词的复数形式。
and that dogs is simply the plural form of the word dog.

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这种方法的另一个问题是，
Another issue with this approach,

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是语言中有很多不同的词。
is that there are a lot of different words in the language.

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如果我们想让我们的模型理解
If we want our model to understand

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该语言中所有可能的句子，
all possible sentences in that language,

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那么我们需要为每个不同的词设置一个 ID。
then we will need to have an ID for each different word.

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以及总字数，
And the total number of words,

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也称为词汇量大小，
which is also known as the vocabulary size,

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可以很快变得非常大。
can quickly become very large.

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这是一个问题，因为每个 ID 都映射到一个大向量
This is an issue because each ID is mapped to a large vector

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代表这个词的意思，
that represents the word's meaning,

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并实现保持这些映射
and keeping track of these mappings

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需要很大的模型
requires an enormous number of weights

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当词汇量很大时。
when the vocabulary size is very large.

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如果我们希望我们的模型保持精简，
If we want our models to stay lean,

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我们可以选择让分词器忽略某些词
we can opt for our tokenizer to ignore certain words

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我们不一定需要的。
that we don't necessarily need.

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例如，在这里，当在文本上训练我们的分词器时，
For example, here, when training our tokenizer on a text,

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我们可能只想使用 10,000 个最常用的单词
we might want to take only the 10,000 most frequent words

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在该文本中。
in that text.

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而不是从该文本中提取所有单词
Rather than taking all words from in that text

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或所有语言的单词来创建我们的基本词汇。
or all languages words to create our basic vocabulary.

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分词器将知道如何转换这 10,000 个单词
The tokenizer will know how to convert those 10,000 words

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转换成数字，但任何其他词都会被转换
into numbers, but any other word will be converted

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作为词汇外的词，
to the out-of-vocabulary word,

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或者像这里显示的那样，未知的词。
or like shown here, the unknown word.

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不幸的是，这是一种妥协。
Unfortunately, this is a compromise.

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该模型将具有完全相同的表示
The model will have the exact same representation

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对于所有它不知道的单词，
for all words that it doesn't know,

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这可能会导致大量信息丢失
which can result in a lot of lost information

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如果存在许多未知单词。
if many unknown words are present.

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