Synonym handling in Elasticsearch - Mini Project: Build & Apply

Synonym Handling in Elasticsearch

📖 Scenario: You are building a search feature for an online bookstore. You want users to find books even if they use different words that mean the same thing. For example, searching for "sci-fi" should also find books tagged with "science fiction".

🎯 Goal: Create an Elasticsearch index with a synonym filter so that searches recognize synonyms. You will define synonyms, apply them in an analyzer, and then create the index using that analyzer.

📋 What You'll Learn

Create a synonym filter named book_synonym_filter with these synonyms: "sci-fi, science fiction" and "ya, young adult"

Create a custom analyzer named book_synonym_analyzer that uses the standard tokenizer and the book_synonym_filter

Create an index named books that uses the book_synonym_analyzer for the title field

💡 Why This Matters

🌍 Real World

Synonym handling improves search results by matching different words with the same meaning, making search more user-friendly and effective.

💼 Career

Understanding how to configure analyzers and filters in Elasticsearch is essential for roles involving search engine development, data indexing, and improving user search experience.

1

Define the synonym filter

Create a filter called book_synonym_filter with type synonym and include these synonyms exactly: "sci-fi, science fiction" and "ya, young adult".

Elasticsearch

{
  "settings": {
    "analysis": {
      "filter": {
        // Define the synonym filter here
      }
    }
  }
}

Hint

Use the filter section inside analysis to define book_synonym_filter with the synonym type and list the synonyms as an array.

2

Create the synonym analyzer

Add an analyzer named book_synonym_analyzer that uses the standard tokenizer and applies the book_synonym_filter filter.

Elasticsearch

{
  "settings": {
    "analysis": {
      "filter": {
        "book_synonym_filter": {
          "type": "synonym",
          "synonyms": [
            "sci-fi, science fiction",
            "ya, young adult"
          ]
        }
      },
      "analyzer": {
        // Add book_synonym_analyzer here
      }
    }
  }
}

Hint

Inside analysis, add an analyzer section. Define book_synonym_analyzer with the standard tokenizer and apply the book_synonym_filter in the filter list.

3

Create the books index with the analyzer

Create an index named books with the book_synonym_analyzer applied to the title field in the mappings.

Elasticsearch

{
  "settings": {
    "analysis": {
      "filter": {
        "book_synonym_filter": {
          "type": "synonym",
          "synonyms": [
            "sci-fi, science fiction",
            "ya, young adult"
          ]
        }
      },
      "analyzer": {
        "book_synonym_analyzer": {
          "tokenizer": "standard",
          "filter": ["book_synonym_filter"]
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "title": {
        // Apply the book_synonym_analyzer here
      }
    }
  }
}

Hint

In the mappings section, set the title field to type text and assign the book_synonym_analyzer as its analyzer.

4

Complete the index creation JSON

Ensure the JSON includes the settings with analysis filters and analyzers, and the mappings with the title field using the book_synonym_analyzer. This completes the Elasticsearch index setup for synonym handling.

Elasticsearch

{
  "settings": {
    "analysis": {
      "filter": {
        "book_synonym_filter": {
          "type": "synonym",
          "synonyms": [
            "sci-fi, science fiction",
            "ya, young adult"
          ]
        }
      },
      "analyzer": {
        "book_synonym_analyzer": {
          "tokenizer": "standard",
          "filter": ["book_synonym_filter"]
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "title": {
        "type": "text",
        "analyzer": "book_synonym_analyzer"
      }
    }
  }
}
# This is the complete JSON for the index creation

Hint

Review the entire JSON to confirm it has all parts: settings with filters and analyzers, and mappings with the title field using the synonym analyzer.

Practice

1. What is the main purpose of synonym handling in Elasticsearch?

easy

A. To find search results that include different words with the same meaning

B. To speed up the indexing process

C. To store data in multiple languages automatically

D. To encrypt search queries for security

Solution

1. Step 1: Understand synonym handling concept

   Synonym handling allows Elasticsearch to match words that mean the same, improving search results.

2. Step 2: Identify the main goal

   The goal is to find results with different words but same meaning, not speed or encryption.

3. Final Answer:

   To find search results that include different words with the same meaning -> Option A

4. Quick Check:

   Synonym handling = find similar meaning words [OK]

Hint: Synonyms help find words with same meaning [OK]

Common Mistakes:

• Thinking synonyms speed up indexing
• Confusing synonyms with encryption
• Assuming synonyms translate languages automatically

2. Which of the following is the correct way to define a synonym filter in Elasticsearch settings?

easy

A. "filter": { "synonym_filter": { "type": "keyword", "synonyms": ["quick,fast"] } }

B. "filter": { "synonym_filter": { "type": "stop", "synonyms": ["quick,fast"] } }

C. "filter": { "synonym_filter": { "type": "synonym", "synonyms": ["quick,fast"] } }

D. "filter": { "synonym_filter": { "type": "stemmer", "synonyms": ["quick,fast"] } }

Solution

1. Step 1: Identify correct filter type for synonyms

   The filter type for synonyms must be "synonym" to handle synonym lists.

2. Step 2: Check the filter definition syntax

   "filter": { "synonym_filter": { "type": "synonym", "synonyms": ["quick,fast"] } } correctly uses "type": "synonym" and defines synonyms as a list.

3. Final Answer:

   "filter": { "synonym_filter": { "type": "synonym", "synonyms": ["quick,fast"] } } -> Option C

4. Quick Check:

   Synonym filter type = "synonym" [OK]

Hint: Synonym filters use type "synonym" [OK]

Common Mistakes:

• Using wrong filter types like stop or stemmer
• Not defining synonyms as a list
• Misspelling "synonym" type

3. Given this analyzer configuration, what will be the tokens produced for the text "fast car"?

{
  "analysis": {
    "filter": {
      "synonym_filter": {
        "type": "synonym",
        "synonyms": ["fast,quick"]
      }
    },
    "analyzer": {
      "synonym_analyzer": {
        "tokenizer": "standard",
        "filter": ["lowercase", "synonym_filter"]
      }
    }
  }
}

medium

A. ["fast", "quick", "car", "car"]

B. ["fast", "quick", "car"]

C. ["quick", "car"]

D. ["fast", "car"]

Solution

1. Step 1: Analyze the text with the synonym filter

   The synonym filter maps "fast" to "quick", so both tokens appear for "fast".

2. Step 2: List all tokens after analysis

   Tokens are "fast", "quick" (synonym), and "car" (unchanged).

3. Final Answer:

   ["fast", "quick", "car"] -> Option B

4. Quick Check:

   Synonym adds "quick" token for "fast" [OK]

Hint: Synonym filter adds synonyms as extra tokens [OK]

Common Mistakes:

• Ignoring synonym addition and listing only original tokens
• Replacing original token instead of adding synonym
• Duplicating tokens unnecessarily

4. You defined a synonym filter but your search results do not include synonyms. What is the most likely mistake?

medium

A. You used the synonym filter in the index but not in the search analyzer

B. You forgot to add the synonym filter to the analyzer's filter list

C. You defined synonyms as a string instead of a list

D. You used the synonym filter with the wrong tokenizer

Solution

1. Step 1: Understand how synonym filters affect search

   Synonyms must be applied in the analyzer used during search to affect results.

2. Step 2: Identify common setup mistake

   Often synonyms are applied only at index time, missing search analyzer usage.

3. Final Answer:

   You used the synonym filter in the index but not in the search analyzer -> Option A

4. Quick Check:

   Synonyms must be in search analyzer too [OK]

Hint: Apply synonym filter in both index and search analyzers [OK]

Common Mistakes:

• Adding synonym filter only at index time
• Not including synonym filter in search analyzer
• Misconfiguring synonyms as string instead of list

5. You want to improve search for a product catalog where users may search for "tv", "television", or "smart tv". How should you configure synonyms to handle these terms effectively?

hard

A. Apply synonyms only at search time to avoid changing indexed data

B. Define synonyms only for "tv" and "television" but exclude "smart tv" because it has two words

C. Use a stop filter to remove "smart" and then define synonyms for "tv" and "television"

D. Define synonyms as: "tv, television, smart tv" in a synonym filter and apply it in both index and search analyzers

Solution

1. Step 1: Define all related terms as synonyms

   Include "tv", "television", and "smart tv" together to cover all user queries.

2. Step 2: Apply synonym filter in both index and search analyzers

   This ensures synonyms work during indexing and searching for best results.

3. Final Answer:

   Define synonyms as: "tv, television, smart tv" in a synonym filter and apply it in both index and search analyzers -> Option D

4. Quick Check:

   Synonyms cover all terms and apply at both stages [OK]

Hint: Include all terms and apply synonyms at index and search [OK]

Common Mistakes:

• Ignoring multi-word synonyms like "smart tv"
• Applying synonyms only at search time
• Using stop filter incorrectly to remove words