🔍 Inverted Search

A menu-driven Inverted Search Engine developed in C using Hash Tables, Linked Lists, and File Handling. The project indexes words from multiple text files and enables fast keyword-based searching by maintaining an inverted index.

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📖 Overview

Searching through multiple text files sequentially is inefficient as the number of files grows. This project implements an Inverted Search mechanism that preprocesses the files and builds an index for quick retrieval.

Each unique word is mapped to:

• The files in which it appears.
• The number of occurrences in each file.

The project demonstrates the practical application of Data Structures and File Handling concepts in C.

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✨ Features

• ✅ Create database from multiple text files
• ✅ Display the complete inverted database
• ✅ Search for a word efficiently
• ✅ Update the database by adding new files
• ✅ Save the database to a file
• ✅ Validate input files before processing
• ✅ Detect duplicate files
• ✅ Handle empty files
• ✅ Validate file extensions
• ✅ Collision handling using linked lists
• ✅ Modular implementation with separate source files

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🛠 Technologies Used

• Language: C
• Data Structures:
  • Hash Table
  • Singly Linked List
• Concepts:
  • Dynamic Memory Allocation
  • File Handling
  • String Manipulation
  • Modular Programming
• Build Tool:
  • Makefile

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📂 Project Structure

.
├── main.c
├── validation.c
├── create_database.c
├── create_file_list.c
├── search_database.c
├── display_database.c
├── save_database.c
├── update_database.c
├── inverted.h
├── Makefile
├── sample text files
└── README.md

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⚙️ Working Principle

The project creates an inverted index using 27 hash buckets.

• Buckets 0–25 represent the letters a–z
• Bucket 26 stores words beginning with digits or special characters

Each bucket points to a linked list of Main Nodes.

Each Main Node stores:

• File Count
• Word
• Pointer to Sub Node List
• Pointer to next Main Node

Each Sub Node stores:

• Word Count
• File Name
• Pointer to Next File

Hash Table
    |
    +---- Bucket[0]
    |         |
    |         +---- Word: apple
    |                    |
    |                    +---- file1.txt (5)
    |                    |
    |                    +---- file3.txt (2)
    |
    +---- Bucket[1]
    |
    +---- ...

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🚀 How to Build

Run

./inverted_search file1.txt file2.txt file3.txt

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📋 Menu

1. Create Database
2. Display Database
3. Search Database
4. Save Database
5. Update Database
6. Exit

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✅ File Validation

Before creating the database, the project validates every input file by checking:

• Valid .txt extension
• File existence
• Empty files
• Duplicate files

Only valid files are inserted into the file list and indexed.

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🔎 Search Operation

When the user searches for a word:

• The hash index is calculated.
• The corresponding bucket is accessed.
• The linked list is traversed.
• Matching word details are displayed, including:
  • File names
  • Number of occurrences

This provides efficient lookup compared to searching every file individually.

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💾 Save Database

The complete inverted database can be saved into a text file, allowing the indexed data to be reused without rebuilding the database.

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🔄 Update Database

New text files can be added after the database has already been created.

The project validates the new file, checks for duplicates, updates the file list, and indexes only the newly added file without rebuilding the existing database.

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📷 Output Screenshots

Validation & Database Creation

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Display Database

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Search Word

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Update Database

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Save Database

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📚 Concepts Demonstrated

• Hash Tables
• Linked Lists
• File Handling
• Dynamic Memory Allocation
• String Handling
• Data Indexing
• Searching Algorithms
• Collision Handling
• Modular Programming

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🎯 Learning Outcomes

This project strengthened my understanding of:

• Designing real-world applications using Data Structures
• Implementing hash-based indexing
• Efficient searching techniques
• File processing in C
• Dynamic memory management
• Writing modular and maintainable C programs

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