Components of a Database System

• Typically four components
  • Users - The people who use the system
  • Database Application - The Application specific programs used to manage the data.
  • Database Management System (DBMS) - A program used to manage the data in the system.
  • Database - the actual data in the system, the tables.
  
• An additional component is the language used to interact with the system the Structured Query Language (SQL)
  • the DBMS receives SQL commands to store, retrieve and manipulate the database.
  • The application generates SQL commands to send to the DBMS to perform these manipulations.
  • The application receives data from the DBMS to present to the users.
• DBMS software is most usually a professionally developed product, which is purchased, with support, from a vendor.
• The database application is usually developed in house, that is what we are preparing to do.
• As well as how to construct the database. (Design and Implementation)
• The users interact with the application through forms.
• Applications and SQL
  • The basic things applications do are
    • Create and process forms
    • Process user queries
    • Create and process reports
    • Execute application logic
    • Control applications
  • A typical ? form
    • 
    • Users can add information to the CLASS table.
    • This will generate a SQL command like

      Insert into CLASS 
                (ClassNumber, ClassName, Term, Section)
                values (100, 'CSCI 313', 'Spring-2013', 1)
      	};
      	

    • 
    • The user needs to know nothing about the tables, structure, data, ...
  • A typical? Query
    • 
    • The user requests the report.
    • The application software generates the SQL query
    • 
    • This query is sent to the DBMS
    • Which extracts the data and returns it to the application
    • Which formats and displays and (possibly) allows interaction with the data.
  • A typical report
    • The same as a query, but perhaps not interactive.
  • Additional functions
    • Control the addition or deletion of data to the database.
    • Not what is legal to change in the db, but what should be changed.
    • An order for 10 items is placed, but only 8 are in stock. What should happen?
      • Deny the order
      • Allow an order of 8 and place 2 on back order?
    • This is the task of the application.
  • Finally
    • Control access to the DB
    • Make sure only logical operations can happen
    • Synchronization and such (at a high level).
• DBMS
  • Manages the data.
  • Data is a generic item to this software.
  • It does not "understand" what is being done with the data
  • (As opposed to the database application)
  • Almost always a licensed product from a professional company.
  • They support the management of data across file systems.
  • It supports organization of the data for faster accesses under specified conditions. (Creation of an index)
  • Enforces rules related to data values, dependencies, ...
  • Synchronization and concurrency control (at a low level)
  • Maintenance and backup.
• The Database
  • "A self-describing collection of integrated tables"
  • Stores both data and relationships between those data.
    • Because of location in a table
    • Also because of relations between tables.
  • self-describing
    • Contains information about the data (format, length, ...)
    • This is called metadata
  • Other items stored:
    • Security information
    • Supporting code from the user
    • Indexes
    • Backup/Recovery information