Storage and File Structure

1. We have been looking mostly at the higher-level models of a database. At the conceptual or logical level the database was viewed as
   • A collection of tables (relational model).
   • A collection of classes of objects (object-oriented model).
2. The logical model is the correct level for database users to focus on. However, performance depends on the efficiency of the data structures used to represent data in the database, and on the efficiency of operations on these data structures.

• Overview of Physical Storage Media
• Magnetic Disks
  • Physical Characteristics of Disks
  • Performance Measures of Disks
  • Optimization of Disk-Block Access
• RAID: Redundant Arrays of Inexpensive Disks (Not covered)
• Tertiary Storage
  • Optical Disks
  • Magnetic Tapes
• Storage Access
  • Buffer manager
  • Buffer replacement policies
• File Organization
  • Fixed-Length Records
  • Variable-Length Records
    • Byte string representation
    • Fixed-length representation
• Organization of Records in Files
  • Sequential File Organization
  • Clustering File Organization
• Data Dictionary Storage
• Storage Structures for Object-Oriented Databases (Omitted)
  • Mapping of Objects to Files
  • Implementation of Object Identifiers
  • Management of Persistent Pointers: Pointer swizzling vs.\ hardware swizzling
  • Disk versus Memory Structure of Objects
  • Large Objects