Introduction to DBMS having data recovery

Introduction to DBMS having data recovery

• 1.
  Introduction Introduction
• 2.
  Outline • The Needfor Databases • Data Models • Relational Databases • Database Design • Storage Manager • Query Processing • Transaction Manager
• 3.
  Database Management System(DBMS) • DBMS contains information about a particular enterprise • Collection of interrelated data • Set of programs to access the data • An environment that is both convenient and efficient to use • Database Applications: • Banking: transactions • Airlines: reservations, schedules • Universities: registration, grades • Sales: customers, products, purchases • Online retailers: order tracking, customized recommendations • Manufacturing: production, inventory, orders, supply chain • Human resources: employee records, salaries, tax deductions • Databases can be very large. • Databases touch all aspects of our lives
• 4.
  University Database Example •Application program examples • Add new students, instructors, and courses • Register students for courses, and generate class rosters • Assign grades to students, compute grade point averages (GPA) and generate transcripts • In the early days, database applications were built directly on top of file systems
• 5.
  Drawbacks of usingfile systems to store data • Data redundancy and inconsistency • Multiple file formats, duplication of information in different files • Difficulty in accessing data • Need to write a new program to carry out each new task • Data isolation • Multiple files and formats • Integrity problems • Integrity constraints (e.g., account balance > 0) become “buried” in program code rather than being stated explicitly • Hard to add new constraints or change existing ones
• 6.
  Drawbacks of usingfile systems to store data (Cont.) • Atomicity of updates • Failures may leave database in an inconsistent state with partial updates carried out • Example: Transfer of funds from one account to another should either complete or not happen at all • Concurrent access by multiple users • Concurrent access needed for performance • Uncontrolled concurrent accesses can lead to inconsistencies • Example: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same time • Security problems • Hard to provide user access to some, but not all, data Database systems offer solutions to all the above problems
• 7.
  Levels of Abstraction •Physical level: describes how a record is stored. • Logical level: describes data stored in database, and the relationships among the data. • View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
• 8.
  View of Data Anarchitecture for a database system
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  Instances and Schemas •Similar to types and variables in programming languages • Logical Schema Logical Schema – the overall logical structure of the database • Example: The database consists of information about a set of customers and accounts in a bank and the relationship between them Analogous to type information of a variable in a program • Physical schema Physical schema– the overall physical structure of the database • Instance – the actual content of the database at a particular point in time • Analogous to the value of a variable • Physical Data Independence – the ability to modify the physical schema without changing the logical schema • Applications depend on the logical schema • In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.
• 10.
  Data Models • Acollection of tools for describing • Data • Data relationships • Data semantics • Data constraints • Relational model • Entity-Relationship data model (mainly for database design) • Object-based data models (Object-oriented and Object- relational) • Semistructured data model (XML) • Other older models: • Network model • Hierarchical model
• 11.
  Source: Database SystemsConcepts by Korth, Silberschatz and Sudarshan