overviewof-中山大学软件学院-OverviewofDatabaseSystems.pptVIP

Example of Transaction Incomplete Transaction and System Crashes Incomplete transaction Canceled by the transaction or DBMS Aborted unexpectedly by system crash Idea: Keep a log (history) of all actions carried out by the DBMS while executing a set of transactions: Before a change is made to the database, the corresponding log entry is forced to a safe location. (WAL protocol; OS support for this is often inadequate.) After a crash, the effects of partially executed transactions are undone using the log. STRUCTURE OF A DBMS Databases make these folks happy ... End users and DBMS vendors DB application programmers E.g., smart webmasters Database administrator (DBA) Designs logical /physical schemas Handles security and authorization Data availability, crash recovery Database tuning as needs evolve Must understand how a DBMS works! Summary DBMS used to maintain, query large datasets. Benefits include recovery from system crashes, concurrent access, quick application development, data integrity and security. Levels of abstraction give data independence. A DBMS typically has a layered architecture. DBAs hold responsible jobs and are well-paid! DBMS RD is one of the broadest, most exciting areas in CS. We focus on Relational DBMS: maintain/query structured data Overview of Database Systems Jianlin Feng School of Software SUN YAT-SEN UNIVERSITY courtesy of Joe Hellerstein and etc for some slides. What is a Database ? Data (/definition/american_english/data. ) facts and statistics collected together for reference or analysis. A Database: Data + Base A very large, structured collection of data. Models some real-world “enterprise”, such as a university Entities e.g., students, courses Relationships e.g., Zhang San is taking the Database System course. What is a Database Management System? A Database Management System (DBMS) is: A software system designed to store, manage, and facilitate query to databases. Popular DBMS Oracle IBM DB2 Microsoft SQL Server Database