Introduction to Database systems Week 2

What is a database? A base of data, collected in some sort of a file system Flat-file Text file Comma Seperated (CSV) XML - formats Code files Books Advanced filecollections Spreadsheet DBMS filesystems

Textbased command system What is a DBMS? Database management system Textbased command system - Ability to provide advanced interaction of data - Manages users - Manages access - Manages rules - Manages events - Security And a lot more Database manager UI Service setup UI Advanced reporting UI Programs Services File formats Event management Linking services Broadcasting Proprietary system of storing data

The landscape of databases Vendor Major DBMS Minor DBMS Microsoft SQL server Access / SQL server express (free) Oracle OracleDB ? IBM DB2 MySQL (oracle) MySQL (free?) MySQL (free) Free versions usually have limitations built in! There are other DB-systems and vendors out there!

What is data? A piece of information, which cannot hold more than one meaning Examples: Name Age Street City economic numbers

What is data? Redundancy Inconsistency - Concurrency issues Name Postalnr City Jens 7100 Vejle Lotte Hanne 6000 Kolding Børge Name Postalnr City Jens 6000 Vejle 7100 Hanne 6200 Aabenraa Børge 6400 Sønderborg - Error prone - Time waste - Concurrency issues

Exercise Can redundancy be a good thing? Is there any form of data where its a good thing to have redundant but concurrent databases? Sure they hold same versions of data!

What is Metadata? Examples Maximum length Text No text Between values Data that describes the properties and expectations towards data Examples Maximum length Text No text Between values Must be filled

Exercise Name Age Birtday Address Possible metadata ?

Types of database usage (academic) Single user / desktop Desktop programs Online and nonline games Multiuser Services x programs at any time Online games Centralised vs. Distributed Operational / production database Economic data DB for industrial production Banking databases Historical database Old data kept for warehouse purposes Data warehouse Statistical collections Strategic data

A bit about ORM´s Object relation management Problem! Creating code to handle getting data to and from a database is cumberson and timeconsuming Solutions! Automation via metadata-mapping More or less automation of CRUD operations Create Read Update Delete

Elements of a database Data Typical valuetypes of data (name may vary) Text – variable length of characters Integer – a number with no , or . separation (whole number) Decimal – a number with room for , or . separation

Elements of a database Table Column Column / domain xyz Row / Tuple Field / datafield Data in field Table A set of data from a row together = record

Elements of a database File Physical file (server) The actual bunch of 0 and 1 on the harddrive Virtual file (server / app) A file that only exist in the RAM Dataset (app) A virtual file consisting of tables Table (server / app) A collection of rows/records of data

Elements of a database server A server can mean different things Physical machine You can touch this Virtual machine OS instances living in RAM Software Instances of programs living in RAM