1. Database-systems, introduction1 1. Database-systems Introduction

1. Database-systems, introduction2 Definitions Database = a collection of data –E.g. information about students records DBMS (database management system) –A collection of programmes for administration of a database –E.g. Access, Oracle, Informix and many others

1. Database-systems, introduction3 DBMS tasks Save data i a file system - effective Transactions: Controlle many concurrent users Recovery: Data must not be lost because of programme errors Interface to a programming langauge e.g. Java And many other things

1. Database-systems, introduction4 History 1960 –Different types of DBMS / file-systems 1970 –Codd plublish the relational model 1970 –First relational DBMS Later –Other models is introduced

1. Database-systems, introduction5 Use of Databases Databases is everywhere Many toys has included a database Banks and other companies uses very big DBMS installations

1. Database-systems, introduction6 Users DBA (Database Administrator) –Creates databases, tables, users etc. Application-programmer –Uses information from the database tables in his programming Database programmer (designs DBMS)

1. Database-systems, introduction7 Users End-user –Uses a program that is connected to the database. –Perhaps the end-user don’t know that there is a database ’behind the scene’ Database programmer (designs DBMS)

1. Database-systems, introduction8 Comparison with a file system Filesystems don’t have: –Effective search mechanismen Index’es –Standard query-langauge SQL –Security Different users with different rights –View’s Different views on the same database/table

1. Database-systems, introduction9 Query processing Queryes is often written in SQL –select firstname, Lastname from student where course = ’Datalogi’ DBMS checks querey –Syntacs: Is the writing correct? –Semantics: Does it have a meaning? DBMS finds the result

1. Database-systems, introduction10 Transaction Transaction: A collection af logical connected working actions on a database. E.g.: Move mony from one account to an other. –Withdraw from account A –Insert the mony on account B

1. Database-systems, introduction11 Transaction II 4 characteristics (ACID) –Atomicity One transaction is indivisibility. Do it all – or not at all. No half transactions. –Consistency Change the database from one consistend mode to an other consistand mode.

1. Database-systems, introduction12 Transaktioner III 4 characteristics (continued) –Isolation Lives isolated from other transactions (Other transactions can’t se results while not finished) –Durability Result from a finished transaction my never disappear