Databases and Database Users

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Databases and Database Users
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Basic Definitions

• Database
• Represents some aspect of the real world
• Coherent collection of data with inherent meaning
• Built for a specific purpose
• Database Management System (DBMS)
• A general-purpose software package/system that
  facilitates the process of defining,
  constructing, manipulating, and sharing
  databases.
• Protects and maintains the database
• Database System The database and DBMS software.

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An Example

• A UNIVERSITY database
• Entities STUDENT, COURSE, SECTION (of COURSE),
  DEPARTMENT, INSTRUCTOR
• Relationships
• SECTIONs are of specific COURSEs
• STUDENTs take SECTIONs
• COURSEs have prerequisite COURSEs
• INSTRUCTORs teach SECTIONs
• COURSEs are offered by DEPARTMENTs
• STUDENTs major in DEPARTMENTs

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Database Approach

• Characteristics
• Self-describing nature of a database system
• A DBMS catalog stores the description of the
  database. The description is called meta-data).
• Allows the DBMS software to work with different
  databases.
• Insulation between programs and data
• Program-data independence
• Allows changing data storage structures and
  operations without having to change the DBMS
  access programs.

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Database Approach

• Characteristics
• Data Abstraction
• A data model is used to hide storage details and
  present the users with a conceptual view of the
  database.
• Support of multiple views of the data
• Each user may see a different view of the
  database, which describes only the data of
  interest to that user.

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Database Technology

• Additional Benefits
• Controlling redundancy in data storage and in
  development and maintenance efforts
• Restricting unauthorized access to data
• Providing persistent storage for program objects
• Providing storage structures for efficient query
  processing
• Providing backup and recovery
• Providing multiple user interfaces

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Database Technology

• Additional Benefits
• Representing complex relationships among data
• Enforcing integrity constraints
• Permitting inferencing and actions using rules
• Flexibility to change data structures
• Potential for enforcing standards
• Reduced application development time
• Availability of up-to-date information
• Economies of scale

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The redundant storage of data items. (a)
Controlled redundancyIncluding StudentName and
CourseNumber in the grade_report file. (b)
Uncontrolled redundancy A GRADE_REPORT record
that is inconsistent with the STUDENT records
inFigure 1.2, because the Name of student number
17 is Smith, not Brown.