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CS3431 – Database Systems I

CS3431 – Database Systems I. Introduction Instructor: Elke A. Rundensteiner rundenst@cs.wpi.edu. What is a Database System?. Database: a large collection of related data. usually too large to fit in computer memory at once. Focus: information, rather than computation. ?.

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CS3431 – Database Systems I

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  1. CS3431 –Database Systems I Introduction Instructor: Elke A. Rundensteiner rundenst@cs.wpi.edu Rundensteiner-CS3431

  2. What is a Database System? • Database: • a large collection of related data usually too large to fit in computer memory at once Focus: information, rather than computation Rundensteiner-CS3431

  3. ? Database Applications Have you ever used a database application? • E-commerce: books etc at Amazon, B&N • Banks -- your valuable $$ and ATM transactions • Airlines – manage flights to get you places • Universities – manage student enrollment • GIS (Maps) – find restaurants closest to WPI • WWW (World Wide Web) – blobs, wikis, etc. • Bio-informatics (genome data) Datasets increasing in diversity and volume everywhere !!! Rundensteiner-CS3431

  4. Example Database : Relational Tabular View of Data: Airline System Flight Passenger FlewIn • Tabular view of data is called Relational Model Rundensteiner-CS3431

  5. Basic Terminology • Data Model: • A collection of “types” used for describing data • Schema: • Describes structures for a particular application, using the given model • Database : • Collection of actual data that conforms to given schema • Database Management System : • Software that allows us to create, use and maintain a database (conforming to given model). Rundensteiner-CS3431

  6. Example Database : Relational Tabular View of Data: Airline System Flight Passenger FlewIn Rundensteiner-CS3431

  7. Relational Data Models • The relational model of data • The most widely used model today. • Main concept: relation, basically a table with rows and columns. • Every relation has a schema, which describes the columns, or fields. Rundensteiner-CS3431

  8. Levels of Abstraction • External schema (view) --describes how users see the data • Logical schema – • describes the logical structures used • Physical schema -- describes files and indexes Rundensteiner-CS3431

  9. Levels of Abstraction: Example • Logical (Conceptual) Schema: • Flight, Passenger, FlewIn tables • Physical Schema • Flight table stored as a sorted file • Index on flightNo attribute for Flight relation • Views ( External Schema ) • NoOfPassengers (flightNo, date, numPassengers) Rundensteiner-CS3431

  10. Why use DBMS, and not files? • Data independence (robustness under change) • Efficient access even on huge data sets • Reduced application development time • Data integrity ensures consistency of data even with multiple users • Recovery from crashes, security, etc. Rundensteiner-CS3431

  11. Data Independence • Applications insulated from how data is structured and stored. • Logical data independence: • Logical schema can change, but views need not change • Protection from changes in logical structure of data. • Physical data independence: • Protection from changes in physical structure of data. • Physical schema such as indexes can change, but logical schema need not change. Rundensteiner-CS3431

  12. Efficient access • Indexing : • Indexes gives direct access to “necessary” portion of data, as opposed to sequential access in files. • Costing : • Estimate expected execution times • Query optimization : • Automatically determine and prepare optimal access plans for getting to the data Optimizer = “The Bread and Butter of a DBMS !” Rundensteiner-CS3431

  13. Reduced application development time • Higher level of data abstraction • Queries are written in a high level language tailored for database applications • Example : SELECT pname FROM Passengers WHERE flightNo = 101 Rundensteiner-CS3431

  14. Data Integrity • DBMS ensures data is consistent under concurrent access • E.g.: multiple airline staff trying to reserve a seat for different customers. • Concepts: • Transactions – grouping multiple instructions (reads/writes) into one atomic unit • Locks – locking of resources (tables) Rundensteiner-CS3431

  15. Recovery from Crashes • If system crashes in middle of transaction, recovery must be provided : • Cannot afford to loose data • Ideas: logging, commit/rollback of transactions Rundensteiner-CS3431

  16. Who use databases? • End users • DB application programmers • Database Administrators • Database design • Security, Authorization • Data availability, crash recovery • Database tuning (for performance) Rundensteiner-CS3431

  17. Summary : Why study DBMS? • Need to process large amounts of data increasing • Video, WWW, computer games, geographic information systems (GIS), genome data, digital libraries, etc. • DB administrators and programmers hold rewarding jobs. • DBMS research is one of the most exciting areas in Computer Science !! Rundensteiner-CS3431

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