These often conflict, so we seek a balance. Sequential - data is stored in sequence by primary key value. Indexed sequential - records are stored sequentially and ordered by the index. Example - phone book. Example - Dewey decimal system.
Bitmap indexes a table is created and an entry is made to indicate the value of each attribute.
Hashed - records are stored and retrieved by algorithm. Also called Direct. Inefficient use of space. Clustering files we may store frequently joined data together in order to speed retrievals. Indexes Primary Key Indexes - index provides fast access and uniqueness.