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The ANSI/SPARC Architecture of a Database Environment Lecture 2 Schema and instance database schema the description of the database is called the database schema or intension; specified at the creation of the database not expected to change very often database instance

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schema and instance
Schema and instance
  • database schema
      • the description of the database is called the database schema or intension;
      • specified at the creation of the database
      • not expected to change very often
  • database instance
      • the raw data that populates a database at a particular moment in time is called a database instance of the extension of the database
schemas and mappings
Schemas and mappings
  • schemas
    • external
    • conceptual
    • internal
  • mappings
    • external / conceptual
    • conceptual / internal
  • data catalogue/dictionary  schemas  mappings
program data independence
Program - data independence
  • physical
      • the immunity of application programs to changes at the internal level
  • logical
      • the immunity of application programs to changes at the conceptual level
slide11
Data
  • types
    • primary
    • derived
  • characteristics
    • integrated
    • shared
    • extensive
    • data = raw data + data dictionary
hardware
Hardware
  • storage space
    • permanent / secondary
    • temporary / primary
  • computational power
application programs
Application programs
  • user developed
      • in a third generation language
      • provide an embedded data sub-language
  • provided by developers
      • fourth generation language
      • examples: query processors, statistical packages, reports/forms generators
database management system
Database management system
  • provides support for
    • data manipulation / definition
      • data sub-languages (computationally incomplete)
    • data integrity
    • security control
    • recovery services
    • concurrency facilities
    • data communication
    • accessing the data dictionary
      • why needed? applications’ automatic access to the DB
people
People
  • data administrator
      • relevance and meaning of data; standards; policy
  • database administrator
      • design, implementation and maintenance of the DB
  • application programmers
  • end user
summary
Summary
  • the three level ANSI/SPARC architecture of a database environment
  • the components of a database environment
activity a2
Activity A2

Which role within a database environment would you prefer to be in, if you were able to choose? Why? Which activities would you be interested in performing? How would you like to co-operate with the people performing the other roles?