- Indexing is a mechanism by which the underlying data is mapped for faster retrieval.
- Any data accessing mechanism: Fetch the block of data from the hard disk (secondary/permanent storage) to the primary memory (e.g. RAM). Look for the desired data in the RAM.
- Dense index: a key-value mapping for each of the db records vs.sparse index (only for a subset of the records)
- Multilevel indexing: usually implemented using self-adjusting B trees or B+ trees