DBM databases

• Based on the key/value data abstraction:
  • The value is the data item to be stored.
  • The key is the search key for the data item (the value).
  
  
  
• Random access; any data item can be accessed in constant time.
  
  
• The data to be handled should be simple, but not necessarily homogenous.
  
  
• A DBM database is essentially a hash table that is stored on disk.
  
  
• A hash table is basically an array that is indexed by strings.
  
  
• In principle, the data item (value) can be any string of bytes.
  
  
• In practice, an implementation can often only handle strings, and sometimes of limited sizes.
  
  
• Implementations: DBM (original, obsolete), GDBM (current), Berkeley DB.