Key-Value Detection Module

Purpose

Detect pairs of key-value throughout each page of a document, depending on a certain number of key-value patterns passed onto the pipeline in the configuration.

What it does

Generates new metadata instances for each match of a key-value pair which validate a match above a certain threshold.

Dependencies

Words to Line Module

How it works

1. All the Line elements of a page are searched for matches with a set of predefined keys in the module parameters using a string matching algorithm based on the Sørensen–Dice coefficient. Only the matches with a similarity score higher than a threshold are kept as candidates.
2. The resulting set of matched keys are kept as candidates, and a corresponding value is looked for in the vicinity of the found key (on the right of the separator character: ':' or ';' by default).
3. Each key with its corresponding value is saved as a KeyValueMetadata type and attached to the concerned elements.

Parameters

The configuration of the module is where the key patterns are described. Following is an example of the configuration of the key-value search module:

[
  "key-value-detection",
  {
    "thresholdRatio": 0.8,
    "keyValueDividerChars": [":", ";"],
    "keyPatterns": {
      "Name": ["Name", "Fullname", "User"],
      "Date of admission": ["ADMISSION DATE & TIME", "Adm Date/Time", "Reg/Admit Date"]
    }
  }
]

Here, the keyValueDividerChars describes the sets of characters that are used in the input document to separate the keys from values in a key-pair description. keyPatterns describe objects describing the key names and patterns on which these key names need to be matched. threshold describes the minimum similarity score for candidate substrings matches to pass.

Example

Imagine a document containing the following text:

.....
Name: John
Surnames: Doe
Residence: Fake Street 123
.....

with config:

{
  "thresholdRatio": 0.8,
  "keyValueDividerChars": [
    ":",
  ],
  "keyPatterns": {
    "First Name": [
      "Name", "First Name"
    ],
    "Surname": [
      "Surname", "Surnames", "Last Name"
    ],
    "Address": [
      "Address", "Domicile", "Residence"
    ]
  }
}

document.metadata property after execution of this module:

[
  {
    "id": 1,
    "elements": [
      468,
      476
    ],
    "type": "key-value",
    "data": {
      "keyName": "First Name",
      "keyElements": [
        468
      ],
      "valueElements": [
        476
      ]
    }
  },
  {
    "id": 2,
    "elements": [
      487,
      498
    ],
    "type": "key-value",
    "data": {
      "keyName": "Surname",
      "keyElements": [
        487
      ],
      "valueElements": [
        498,
      ]
    }
  },
  {
    "id": 3,
    "elements": [
      399,
      431
    ],
    "type": "key-value",
    "data": {
      "keyName": "Address",
      "keyElements": [
        399
      ],
      "valueElements": [
        431
      ]
    }
  }
]

Here we can see that 3 matches have been found:

• First Name: Elements with IDs 468 and 476, corresponding to Words with contents "Name" and "John" respectively.
• Surname: Elements with IDs 487 and 498, corresponding to Words with contents "Surnames" and "Doe".
• Address: Elements with IDs 399 and 431, with contents "Residence" and "Fake Street 123"

Note that keyElements and valueElements properties are defined as an array, because more than one match can be found for that key-value pair.

Accuracy

The accuracy is high. There is a direct corelation with the quality of the readability of the input document, the OCR's output, as well as the threshold for acceptance of candidates.

Limitations

The current implementation supposes that key value pairs are always arranged in a single line and in the form key : value. This makes it applicable to only a few limited cases.