Using the annotated-text field

Using the `annotated-text` field

The annotated-text tokenizes text content as per the more common text field (see "limitations" below) but also injects any marked-up annotation tokens directly into the search index:

PUT my-index-000001
{
  "mappings": {
    "properties": {
      "my_field": {
        "type": "annotated_text"
      }
    }
  }
}

Such a mapping would allow marked-up text eg wikipedia articles to be indexed as both text and structured tokens. The annotations use a markdown-like syntax using URL encoding of one or more values separated by the & symbol.

We can use the "_analyze" api to test how an example annotation would be stored as tokens in the search index:

GET my-index-000001/_analyze
{
  "field": "my_field",
  "text":"Investors in [Apple](Apple+Inc.) rejoiced."
}

Response:

{
  "tokens": [
    {
      "token": "investors",
      "start_offset": 0,
      "end_offset": 9,
      "type": "<ALPHANUM>",
      "position": 0
    },
    {
      "token": "in",
      "start_offset": 10,
      "end_offset": 12,
      "type": "<ALPHANUM>",
      "position": 1
    },
    {
      "token": "Apple Inc.", 
      "start_offset": 13,
      "end_offset": 18,
      "type": "annotation",
      "position": 2
    },
    {
      "token": "apple",
      "start_offset": 13,
      "end_offset": 18,
      "type": "<ALPHANUM>",
      "position": 2
    },
    {
      "token": "rejoiced",
      "start_offset": 19,
      "end_offset": 27,
      "type": "<ALPHANUM>",
      "position": 3
    }
  ]
}

Note the whole annotation token Apple Inc. is placed, unchanged as a single token in the token stream and at the same position (position 2) as the text token (apple) it annotates.

We can now perform searches for annotations using regular term queries that don’t tokenize the provided search values. Annotations are a more precise way of matching as can be seen in this example where a search for Beck will not match Jeff Beck :

# Example documents
PUT my-index-000001/_doc/1
{
  "my_field": "[Beck](Beck) announced a new tour"
}

PUT my-index-000001/_doc/2
{
  "my_field": "[Jeff Beck](Jeff+Beck&Guitarist) plays a strat"
}

# Example search
GET my-index-000001/_search
{
  "query": {
    "term": {
        "my_field": "Beck" 
    }
  }
}

	As well as tokenising the plain text into single words e.g. `beck`, here we inject the single token value `Beck` at the same position as `beck` in the token stream.
	Note annotations can inject multiple tokens at the same position - here we inject both the very specific value `Jeff Beck` and the broader term `Guitarist`. This enables broader positional queries e.g. finding mentions of a `Guitarist` near to `strat`.
	A benefit of searching with these carefully defined annotation tokens is that a query for `Beck` will not match document 2 that contains the tokens `jeff`, `beck` and `Jeff Beck`

Any use of = signs in annotation values eg [Prince](person=Prince) will cause the document to be rejected with a parse failure. In future we hope to have a use for the equals signs so will actively reject documents that contain this today.

Synthetic `_source`

edit

Synthetic _source is Generally Available only for TSDB indices (indices that have index.mode set to time_series). For other indices synthetic _source is in technical preview. Features in technical preview may be changed or removed in a future release. Elastic will work to fix any issues, but features in technical preview are not subject to the support SLA of official GA features.

annotated_text fields support synthetic _source if they have a keyword sub-field that supports synthetic _source or if the annotated_text field sets store to true. Either way, it may not have copy_to.

If using a sub-keyword field then the values are sorted in the same way as a keyword field’s values are sorted. By default, that means sorted with duplicates removed. So:

PUT idx
{
  "mappings": {
    "_source": { "mode": "synthetic" },
    "properties": {
      "text": {
        "type": "annotated_text",
        "fields": {
          "raw": {
            "type": "keyword"
          }
        }
      }
    }
  }
}
PUT idx/_doc/1
{
  "text": [
    "the quick brown fox",
    "the quick brown fox",
    "jumped over the lazy dog"
  ]
}

Will become:

{
  "text": [
    "jumped over the lazy dog",
    "the quick brown fox"
  ]
}

Reordering text fields can have an effect on phrase and span queries. See the discussion about position_increment_gap for more detail. You can avoid this by making sure the slop parameter on the phrase queries is lower than the position_increment_gap. This is the default.

If the annotated_text field sets store to true then order and duplicates are preserved.

PUT idx
{
  "mappings": {
    "_source": { "mode": "synthetic" },
    "properties": {
      "text": { "type": "annotated_text", "store": true }
    }
  }
}
PUT idx/_doc/1
{
  "text": [
    "the quick brown fox",
    "the quick brown fox",
    "jumped over the lazy dog"
  ]
}

Will become:

{
  "text": [
    "the quick brown fox",
    "the quick brown fox",
    "jumped over the lazy dog"
  ]
}

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Using the annotated-text field