What are the different types of indexing used in databases for research?

In research databases, several indexing techniques are employed. Common types include B-tree indexing (for efficient range queries), Hash indexing (for exact matches), Full-Text indexing (for searching within text content), and Inverted Indexing (for keyword-based searches). The choice depends on the specific research needs - whether it involves range scans, exact lookups, or natural language queries.