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78 lines
5.3 KiB
Plaintext
78 lines
5.3 KiB
Plaintext
When you call `nlp` on a text, spaCy first tokenizes the text to produce a `Doc`
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object. The `Doc` is then processed in several different steps – this is also
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referred to as the **processing pipeline**. The pipeline used by the
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[trained pipelines](/models) typically include a tagger, a lemmatizer, a parser
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and an entity recognizer. Each pipeline component returns the processed `Doc`,
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which is then passed on to the next component.
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> - **Name**: ID of the pipeline component.
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> - **Component:** spaCy's implementation of the component.
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> - **Creates:** Objects, attributes and properties modified and set by the
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> component.
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| Name | Component | Creates | Description |
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| --------------------- | ------------------------------------------------------------------ | --------------------------------------------------------- | ------------------------------------------------ |
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| **tokenizer** | [`Tokenizer`](/api/tokenizer) | `Doc` | Segment text into tokens. |
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| _processing pipeline_ | | |
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| **tagger** | [`Tagger`](/api/tagger) | `Token.tag` | Assign part-of-speech tags. |
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| **parser** | [`DependencyParser`](/api/dependencyparser) | `Token.head`, `Token.dep`, `Doc.sents`, `Doc.noun_chunks` | Assign dependency labels. |
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| **ner** | [`EntityRecognizer`](/api/entityrecognizer) | `Doc.ents`, `Token.ent_iob`, `Token.ent_type` | Detect and label named entities. |
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| **lemmatizer** | [`Lemmatizer`](/api/lemmatizer) | `Token.lemma` | Assign base forms. |
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| **textcat** | [`TextCategorizer`](/api/textcategorizer) | `Doc.cats` | Assign document labels. |
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| **custom** | [custom components](/usage/processing-pipelines#custom-components) | `Doc._.xxx`, `Token._.xxx`, `Span._.xxx` | Assign custom attributes, methods or properties. |
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The capabilities of a processing pipeline always depend on the components, their
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models and how they were trained. For example, a pipeline for named entity
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recognition needs to include a trained named entity recognizer component with a
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statistical model and weights that enable it to **make predictions** of entity
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labels. This is why each pipeline specifies its components and their settings in
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the [config](/usage/training#config):
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```ini
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[nlp]
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pipeline = ["tok2vec", "tagger", "parser", "ner"]
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```
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<Accordion title="Does the order of pipeline components matter?" id="pipeline-components-order">
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The statistical components like the tagger or parser are typically independent
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and don't share any data between each other. For example, the named entity
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recognizer doesn't use any features set by the tagger and parser, and so on.
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This means that you can swap them, or remove single components from the pipeline
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without affecting the others. However, components may share a "token-to-vector"
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component like [`Tok2Vec`](/api/tok2vec) or [`Transformer`](/api/transformer).
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You can read more about this in the docs on
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[embedding layers](/usage/embeddings-transformers#embedding-layers).
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Custom components may also depend on annotations set by other components. For
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example, a custom lemmatizer may need the part-of-speech tags assigned, so it'll
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only work if it's added after the tagger. The parser will respect pre-defined
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sentence boundaries, so if a previous component in the pipeline sets them, its
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dependency predictions may be different. Similarly, it matters if you add the
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[`SpanRuler`](/api/spanruler) before or after the statistical entity recognizer:
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if it's added before and it is writing to `doc.ents`, then the entity recognizer
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will take those existing entities into account when making predictions. The
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[`EntityLinker`](/api/entitylinker), which resolves named entities to knowledge
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base IDs, should be preceded by a pipeline component that recognizes entities
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such as the [`EntityRecognizer`](/api/entityrecognizer).
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</Accordion>
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<Accordion title="Why is the tokenizer special?" id="pipeline-components-tokenizer">
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The tokenizer is a "special" component and isn't part of the regular pipeline.
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It also doesn't show up in `nlp.pipe_names`. The reason is that there can only
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really be one tokenizer, and while all other pipeline components take a `Doc`
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and return it, the tokenizer takes a **string of text** and turns it into a
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`Doc`. You can still customize the tokenizer, though. `nlp.tokenizer` is
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writable, so you can either create your own
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[`Tokenizer` class from scratch](/usage/linguistic-features#native-tokenizers),
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or even replace it with an
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[entirely custom function](/usage/linguistic-features#custom-tokenizer).
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</Accordion>
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---
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