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UW-Milwaukee COMPSCI 557 - Lecture Notes

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CS 262-557Chapter 1What is a Database?Address BookSeptember 1998Index on CitiesStages in the Life of a DatabaseSlide 8Fig 1.1Slide 10Fig 1.2Slide 12What Problems could the University have regarding access to these tables?Solutionfig 1.4Characteristics of the DBMS ApproachSlide 17Slide 18Slide 19Slide 20DBMS PersonnelChapter 1 1CS 262-557Introduction to DatabaseSystemsChapter 1 2Chapter 1Databases and DatabaseUsersChapter 1 3What 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 4Address BookAlan Arkin200 Olive StreetAnn Arbor, MI 48104313-555-1212Birthday May 10th. . .Mary Ziegler341 Einstein DriveBerkeley, CA 94703510-555-1234Annivsy: July 12thChapter 1 5September 1998Sun Mon Tues Wed Thurs Fri Sat1 2 3 4 56 7 8 9 10John’sBday11 1213 14 15 16 17 18 1920 21 22 23 24 25 2627Sue’sAnnvy28 29 30Chapter 1 6Index on CitiesAnn ArborAnn ArborBerkeleyBerkeleyComptonAllan ArkinJohn DoeSue SmithMary ZieglerJohn LawChapter 1 7Stages 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 9Fig 1.1Chapter 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 11Fig 1.2Chapter 1 12Hypothetical 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 13What Problems could the University have regarding access to these tables?Chapter 1 14Solution• “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 15fig 1.4Chapter 1 16Characteristics 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 desirableChapter 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 21DBMS 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


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