Sem título

Databases

1. Data, information and knowledge

   • Data is words, numbers, dates, images, sounds etc without context.
   • Data items need to be part of a structure, such as a sentence, in order to give them meaning.
   • Information is a collection of words, numbers, dates, images, sounds etc put into context, ie to give them meaning.
   • Input devices can collect data automatically, eg sensors that continually measure a temperature or a fix-mount barcode reader at a till.
   • In both of these cases the data collected will be read into a database for processing. With a structure in place (the database) the data becomes information
   • The car looked like it had flat tyres and it had a pool of petrol underneath it at the back. There was smoke coming from the bonnet. I took the decision not to allow anyone near it and to evacuate the area.
     • In this example the judgement made and the decision that followed, ie to evacuate the area, is the knowledge, gained after assessing the available information.
   • Computers can be programmed with rules to use information to make simple decisions. This is knowledge that has been passed on from the programmer.
     • example of this is a spreadsheetapplication that monitors pupils' test marks and calculates average scores.

2. Databases and data capture

   • Before setting up a database, the record structure must be decided to make best use of the memory and backing store, and to make searching and report creation easier.
   • Before setting up a database, the record structure must be decided to make best use of the memory and backing store, and to make searching and report creation easier.
     • 1.What information is needed? 2.What validation could there be?
   • When designing a database it is important to choose the correct field type. This ensures that the data stored is usable and it makes validation easier
     • For example, if the price paid for goods was stored in a text field, then the database wouldn’t be able to add each individual figure to produce a total.
   • Relational databases
     • A relational database has more than one table and the tables are linked using key fields. For example, a library database could have three tables:
   • Advantages
     • The book's details and the customer's details need only be entered into the database once.
       • Because of this, mistakes are less likely to happen and if there were a mistake in a customer's record, for example, correcting it will correct the mistake database-wide.

3. Queries and SQL

   • Databases allow us to store and filter data to find specific information. A database can be queried using a variety of methods, although this depends on the software you are using.
   • Query language
     • Query language is a written language used only to write specific queries. This is a powerful tool as the user can define precisely what is required in a database. SQL is a popular query language used with many databases.
   • Query by example (QBE)
     • QBE allows the user to create queries based on a template, usually a set of filters presented in a graphical form.
       • If you are using database software it might have an option to connect blocks and set the filters you want. The system presents a blank record and lets you specify the fields and values that define the query.

4. Data validation and verification

   • Validation is an automatic computer check to ensure that the data entered is sensible and reasonable. It does not check the accuracy of data.
     • For example, a secondary school student is likely to be aged between 11 and 16. The computer can be programmed only to accept numbers between 11 and 16. This is a range check.
       • However, this does not guarantee that the number typed in is correct. For example, a student's age might be 14, but if 11 is entered it will be valid but incorrect.
   • There are two main methods of verification
     • Double entry - entering the data twice and comparing the two copies. This effectively doubles the workload, and as most people are paid by the hour, it costs more too.
     • Proofreading data - this method involves someone checking the data entered against the original document. This is also time-consuming and costly.