A database is a vast collection of data pertaining to 
   a specific topic, e.g., nucleotide sequence, protein 
   sequence,  etc.  in  an  electronic  environment. 
   Databases are at the heart of bioinformatics. There 
   is  a  very  large  number  of  databases,  which  is 
   growing rapidly. The biological information can be 
   stored in different databases. Each database has its 
   own  website  with  unique  navigation  tools.  The 
   biological  databases  are,  in  general,  publicly 
   accessible.
  Types of databases: 3 types on the basis of source.
  Primary databases:
    Primary  databases  contain  original  biological  data.  They  are 
  archives  of  raw  sequence  or  structural  data  submitted  by  the 
  scientific community. It can also be called an archival database since 
  it archives the experimental results submitted by the scientists. The 
  primary database is populated with experimentally derived data like 
  genome sequence, macromolecular structure, etc. 
  The data are given accession numbers when they are entered into the 
  database. The same data can later be retrieved using the accession 
  number.  Accession  number  identifies  each  data  uniquely  and  it 
  never changes.
  Examples –
  Nucleotide sequence:
  European Molecular Biology Laboratory (EMBL) database, 
  GenBank and
   DDBJ 
  Protein Databases are: PDB, PIR, Metacyc, etc.
     GenBank
    GenBank  is  physically  located  in  the  USA  and  is 
    accessible through the NCBI portal over the intern.
    The GenBank sequence  database is  open  access, 
    annotated       collection    of      all    publicly 
    available nucleotide sequences                   and 
    their protein translations. This database is produced 
    and  maintained  by  the National  Center  for 
    Biotechnology    Information (NCBI)    as   part   of 
    the International  Nucleotide  Sequence  Database 
    Collaboration (INSDC).  GenBank  has  become  an 
    important database for research in biological fields 
    and  has  grown  in  recent  years  at  an exponential 
    rate by doubling roughly every 18 months.
   EMBL  (European  Molecular  Biology 
   Laboratory)
   EMBL     (European     Molecular   Biology 
   Laboratory)  is  in  UK.  The  European 
   Molecular  Biology  Laboratory  (EMBL) 
   Nucleotide  Sequence  Database  is  a 
   comprehensive  collection  of  primary 
   nucleotide  sequences  maintained  at  the 
   European  Bioinformatics  Institute  (EBI). 
   Data    are    received    from    genome 
   sequencing  centers,  individual  scientists 
   and patent offices.