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CS 262-557

CS 262-557. Introduction to Database Systems. Chapter 1. Databases and Database Users. What is a Database?. A collection of related data. It contains data specific to part of the real world, a miniworld. Consequently, it is a logically coherent collection of data.

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CS 262-557

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  1. CS 262-557 Introduction to Database Systems Chapter 1

  2. Chapter 1 Databases and Database Users Chapter 1

  3. What is a Database? • A collection of related data. • It contains data specific to part of the real world, a miniworld. • Consequently, it is a logically coherent collection of data. • It is maintained for specific applications. Chapter 1

  4. Alan Arkin 200 Olive Street Ann Arbor, MI 48104 313-555-1212 Birthday May 10th . . . Mary Ziegler 341 Einstein Drive Berkeley, CA 94703 510-555-1234 Annivsy: July 12th Address Book Chapter 1

  5. September 1998 Chapter 1

  6. Ann Arbor Ann Arbor Berkeley Berkeley Compton Allan Arkin John Doe Sue Smith Mary Ziegler John Law Index on Cities Chapter 1

  7. Stages in the Lifeof a Database • Definition: specifying structures of tables and data to be stored. • Construction: populating tables with data. • Manipulation: queries, updates, deletes, etc. Chapter 1

  8. A DBMS (database management system) is a general-purpose software that enables users to define, construct and maintain various databases. ie. Oracle, Dbase IV • However, databases have been implemented using a high-level language to define a collection of files. Using programs to access this files. This is traditional file processing. Chapter 1

  9. Fig 1.1 Chapter 1

  10. A database system, which consists of a database together with DBMS software, is the complete environment in which a user operates. Chapter 1

  11. Fig 1.2 Chapter 1

  12. Hypothetical situation: Smith and Brown are on probation and need approval from the instructor of each course that they scored a C or less. What are the names of these courses? Who are the instructors? Suggested changes to tables if these queries are frequent. Chapter 1

  13. What Problems could the University have regarding access to these tables? Chapter 1

  14. Solution • “Virtual” tables or views allows the organization to selectively provide access to information while avoiding concurrency problems. • Views also allow for the creation of dynamic summary views of information. Chapter 1

  15. fig 1.4 Chapter 1

  16. Characteristics of the DBMSApproach • Self-describing nature: Together with each database is stored a system catalog which is a separate entity containing information about each table in the database, types of each data item I.e. metadata! Chapter 1

  17. Insulation between programs & data: Consequence of using metadata. In traditional file processing the structure of the file is embedded in the access program, while with DBMS the structure of a file is defined separately in the system catalog, and is transparent to the access program. E.g.. in the University database if we added extra fields in GRADE_REPORT table, all programs that access this table would have to be rewritten! This is not true with a DBMS. Chapter 1

  18. Support of multiple views: A view may be a subset of the database, or may contain virtual data that is not explicitly stored, but instead it is derived. i.e. TotalHours in STUDENT_DUES. • Sharing of data: A multi-user DBMS provides concurrency control software to allow multiple users to simultaneously access data. Such as bank accounts and airline reservations. Chapter 1

  19. Control of Redundancy: There are 3 main problems with redundancy: • duplication of effort • waste of space • possible inconsistency • In the DBMS approach, redundancy is regulated by centralizing the data in one database, and providing various user groups with the views they need. However, controlled redundancy may sometimes be desirable Chapter 1

  20. Security & Authorization Mechanisms: Consequence of centralization. The DBA may restrict privileges (retrieve, update,etc) by either database, user or user’s role. • Enforcing integrity constraints: A DBMS provides capabilities to enforce constraints or business rules I.e. each student must have a unique studentnumber. • Providing Backup & Recovery: A DBMS provides facilities to recover from either software or hardware failures. Chapter 1

  21. DBMS Personnel • Tool Developers • DBMS Designers • Database Administrator (DBA) • System Analysts • End Users • Casual - occasional high level use • Parametric- frequent canned transactions • Sophisticated - frequent high level use Chapter 1

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