Database Systems Introduction Powerpoint
- 2. 2 Databases Are Everywhere • Database = a large (?) collection of related data • Classically, a DB models a real-world organisation (e.g., enterprise, university) – Entities (e.g., students, courses) – Relationships (e.g., “Martin is taking IDS in 2010/11”) • Changes in the organisation = changes in the database • Examples: – personnel records – banking – airline reservations
- 3. 3 Scientific Databases (Examples) • Biology: e.g., DNA sequences of genes, amino-acid sequences of proteins, genes expressed in tissues (up to several Gigabytes) • Astronomy: e.g., location and spectra of astronomic objects (up to several Terabytes) • Physics: e.g., sensor measurements in particle physics experiments (up to several Petabytes)
- 4. 4 DB Tendencies • Sensors record data Î DBs grow in size Î DBs become more widespread Î date may be less reliable, i.e., uncertain • Multimedia data Î Requirements for larger storage Î New query operations (e.g., find a song by humming the melody, find pictures with a given face) • Data on the Web Î Accessed/changed by many people (Facebook,…) Î Speed up access, loosen consistency (NoSQL)
- 5. 5 Operations with Databases • Design – Define structure and types of data • Construction – Create data structures of DB, populate DB with data • Manipulation of Data – Insert, delete, update – Query: “Which department pays the highest salary?” – Create reports: “List monthly salaries of employees, organised by department, with average salary and total sum of salaries for each dept”
- 6. 6 An Ideal DB Implementation Should Support: • Structure – data types – data behaviour • Persistence – store data on secondary storage • Retrieval – a declarative query language – a procedural database programming language • Performance – retrieve and store data quickly • Data Integrity • Sharing – concurrency • Reliability and resilience • Large data volumes
- 7. 7 Database Management System (DBMS) • A DBMS is a software package designed to store and manage databases • A DBMS provides generic functionality (see previous slide) that otherwise would have to be implemented over and over again Î Reduced application development time • Several brands, e.g., – Oracle Xi/Yg (Oracle), DB2 (IBM), SQL Server, Access (Microsoft), MySQL, PostgreSQL, HSQLDB, SQLite (open source)
- 8. 8 Database Actors Tool Developers Operators and Maintenance Personnel End Users • sophisticated • casual • ‘parametric’ or ‘canned’ transactions Database Designers Database Administrator (DBA) Application Programmers DBMS developers “on the scenes” “behind the scenes” Database Database Management System
- 9. 9 File System: A Physical Interface Student Admin Scheduler Payroll Timetable Year Lists Money Transfer Student Data Lecturer Data Course Data
- 10. 10 Sharing Data: Replication Î Redundancy Student Data Course Data Lecturer Data Student Admin Payroll Teaching Schedule Lab Timetable Tutorials Scheduler
- 11. 11 Sharing Data and Operations Course Data Lecturer Data Student Admin Scheduler Payroll Schedule Lab Timetable Tutorials Student Data Teaching
- 12. 12 DBMS: A Logical Interface University Database Metadata student course lecturer Lab Timetable Teaching Schedule Tutorials Database Management System University Database Data Data Dictionary or System Catalog ?QUERIES
- 13. 13 File System Approach • Uncontrolled redundancy • Inconsistent data • Inflexibility • Limited data sharing • Poor enforcement of standards • Low programmer productivity • Excessive program maintenance • Excessive data maintenance
- 14. 14 DBMS Approach • Controlled redundancy – consistency of data & integrity constraints • Integration of data – self-contained – represents semantics of application • Data and operation sharing – multiple interfaces • Services & controls – security & privacy controls – backup & recovery – enforcement of standards • Flexibility – data independence – data accessibility – reduced program maintenance • Ease of application development
- 15. 15 However.... If an application is • simple • stringent real-time • single user • static, files are the option of choice DBMS downside: • more expensive • more complex • general • In a file system, data is physically accessed and not integrated • In a DBMS, data is logically accessed and integrated: – query language – data dictionary Summary: