Named Entity Recognition 25.2
Named Entity Recognition User and Programming Guide

# Named Entity Recognition Grammar Structure

A Named Entity Recognition grammar defines patterns for matching text in a document. A pattern is a combination of characters and operators. An operator is a sequence of special characters that match text by following the rules associated with the operator.

Pattern | Description | Matches
--- | --- | ---
Smith|John | Match either Smith or John | Smith John
[0-9]{3} | Match a sequence of three characters in the range 0 through 9 | 123 456

In this example, the square bracket operators [] are used to match on any of the characters 0 through 9 and the curly braces {} are used to repeat the previous pattern three times.

Grammars are described using XML. The file `edk.dtd` contains the template that defines the XML that Named Entity Recognition understands. When writing grammars for Named Entity Recognition, OpenText recommends that you reference `edk.dtd` at the start of the XML grammar file using the include statement, and that you use a DTD-compatible XML authoring tool to eliminate syntax errors and save time.

Here is an example of a simple Named Entity Recognition grammar:

    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE grammars SYSTEM "edk.dtd">
    <grammars>
       <grammar name="mygrammar">
          <entity name="name" type="public">
             <pattern>Smith|John</pattern>
          </entity>
          <entity name="digits" type="public">
             <pattern>[0-9]{3}</pattern>
          </entity>
       </grammar>
    </grammars>

This grammar defines two entities: `mygrammar/name` and `mygrammar/digits`.

NOTE: The full name of an entity is the name attribute of the parent grammar, followed by a slash, and then the entity name attribute. For example `mygrammar/name`.

In general, the full name of an entity must be unique, even for entities in different grammar files. This restriction includes private entities that you might reference internally in a grammar. In some cases, non-unique entity names can cause unexpected results when you use multiple grammar files in the same Named Entity Recognition session.

You can ensure that entity names are unique by making sure that the `<grammar>` tag in every source file has a unique value for the name attribute.

An exception to this restriction is when you deliberately extend or replace an existing public entity.

For full details of the Named Entity Recognition grammar XML syntax, and the `edk.dtd`, see Grammar Format Reference.

For a more extensive set of example Named Entity Recognition grammar files, see Example Grammar Files.

Copyright 2013-2025 Open Text
Version 25.2 | Last updated April 2025

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Product: Knowledge Discovery Named Entity Recognition 25.2

Topic Title: Named Entity Recognition Grammar Structure