1. Databases - their construction and use John Dubery, U3A Intermediate Computing April 2011

2. Databases are BIG! E.g. a new Government database is called COINs: it's 120Gb Recently I've read the following about databases: “many of today's databases routinely grow into the 100-800 gigabyte (GB) range.” “databases of 400 GB or more are not uncommon” “Wal-Mart:- in 2004: at more than 500 terabytes, the data warehouse dwarfs other retail databases.” in 2007 - Plans for a 4PB Data Warehouse

3. 1 Terabyte – Tb - is 1000 Gigabytes 1 Petabyte – Pb - is 1000000 Gigabytes in 2007 - Plans for a 4PB Data Warehouse So that's 4,000,000 Gigabytes! Consequently, database software doesn't bring the data into memory even when it's being worked on. This is quite different from a spreadsheet. But databases are highly structured, so the links between chunks of data are stored on disk.

4. Customer1 nameDisk address 1 Customer2 nameDisk address 3 Customer3 nameDisk address 1 Customer4 nameDisk address 5 Customer5 nameDisk address 5 Street address 1 Street address 2 Street address 3 Street address 4 Street address 5 Originally disk addresses were used for the links But this is difficult to maintain, particularly when you need to move chunks of the data around

5. ID 1 ID 2 ID 3 ID 4 ID 5 Customer1 nameID 1 Customer2 nameID 3 Customer3 nameID 1 Customer4 nameID 5 Customer5 nameID 5 Street address 1 Street address 2 Street address 3 Street address 4 Street address 5 So, nowadays Identifiers are created and copied to form the links The lesson is that YOU have to create these identifiers in your own database. Databases that do this are called RELATIONAL

6. Relational Databases Invented by Ted Codd at IBM, California in 1970 Data is arranged in a tabular form, similar to a spreadsheet Links between “chunks” of data are provided by copying identifiers

7. Common Relational Databases Adabas D, DataEase, FileMaker Pro, IBM DB2, IBM Lotus Approach, Informix, Ingres, InterBase, Microsoft Access, Microsoft SQL Server, Microsoft Visual FoxPro, MySQL, Netezza, NonStop SQL, Openbase, Oracle, Sybase SQL Anywhere, Teradata

8. The “Chunks” of data Filesystem File Record Field Database Table Row Column

9. Layout of data Each Table is named Each Column is named The number of tables and the columns they contain are fixed when the database is designed Each column can contain only one type of data, decided at design time e.g. date, money, text The number of rows in each table is indefinite

10. And now A Demo...

11. Extracting (a copy of) the Data – i.e. Queries SHOW ME ArtistName, AlbumTitle, Media FROM THE TABLE Query_All-Music SUCH THAT ArtistName IS LIKE 'Elvis Presley' SHOW ME ArtistName, AlbumTitle, Media FROM THE TABLES Music-Collection AND ArtistID, MATCHING ON ArtistID SUCH THAT ArtistName IS LIKE 'Elvis Presley'

12. And now A Demo...

13. How to Use a Database Maintain the data Insert new rows, update columns, delete old rows Extract “actionable” subsets of the data Regular queries to list items for action  e.g. list of members with overdue subs  e.g. list of deliveries for today  e.g. list of upcoming bills Find all the data related to one account/member/... e.g. at a call centre In businesses the queries would be embedded in programs