Topic 8: Databases

Topic 8: Databases

1. Data types

   • Number integer
     • A whole number (positive or negative) but no fractions.
   • Number real
     • Any number, including whole numbers and fractions.
   • Text or string
     • Letters, numbers or other characters such as punctuation marks.
   • Date/time
     • Any time or date; the way the time or date is displayed depends on how it is formatted.
   • Currency
     • Money £ (including foreign currency $ or €)
   • Boolean
     • Two opposing states e.g. true or false, male or female, yes or no.

2. Table

   • • A field is a single item of data within a record.
     • • surname: text • date of birth: date/time • selling pricing: currency
   • • A record consists of a collection of related fields.
     • • Pupil’s record in a school database only has the fields related to that pupil (surname, forename, date of birth, from, etc.) and not another pupils data.
   • • A file (Known as a table in Microsoft Access) is a collection of related fields.
     • • The table of records of all pupils in the school.
   • Key fields uniquely identities each record. No two records have the same data in their key field.
     • identity number, membership number or bar code.

3. Validation

   • ensure reasonable and sensible data is input in to a system, but there is no certainty that the data is correct.
   • As data is entered it is checked to see that it obeys the rules; any data that does not obey the rules is not accepted.
     • You can also set validation text – the text that appears if the data is not acceptable.
   • Range check
     • The data entered must be in a sensible range.
   • Type check
     • This ensures that the data is of the correct type.
   • Format/picture check
     • If the data entered has a particular pattern e.g. a postcode or car reg then an input mask can be used to force the data to conform to the rule.
   • Length check
     • The length of the input is checked for the number of characters used.
   • Presence check
     • Some data has to be entered.
   • Lookup list
     • If the data entered consists of a limited number of possible entries then the computer can compare the entry with a list of allowed answers.

4. Reports, forms and calculated fields

   • A report is a printed document that contains data from the database, organised and analysed in a certain way.
   • Forms are used to make data entry more attractive and secure rather than entering data into raw tables.
     • allows instructions to be entered
     • the person entering the data need not see all other data or even the other fields
   • If you want to use age in a report it must be calculated. This result is known as a calculated field.
     • use the recorded date of birth to calculate the age by subtracting the date of birth from the date of the report.
   • Sorting data
     • Results of queries can be presented in a sorted order e.g. alphabetical or in numerical order.
     • • Easier if lists a printed as reports.
     • • You can identify best customer by amount they have spent – sort them according to total amount spent.

5. Databases

   • Uses of a database
     • • Add, change or delete records
       • • Search for a particular record
         • • Sort the records into a given order
           • • Print reports about some aspect of the database
   • • Fast access: using a database to find data is much faster compared to paper in a filing cabinet.
     • • Easy to edit: a database allows for data to be easily updated and changed.
       • • Validation: you can set checks on the data being entered to ensure no inappropriate data gets into the system
         • • Reports: results of searches can be used to print reports that may help management in their decision making.
           • • Sharing: database can be shared with any number of users on a network. Any user can edit the data.
             • • Security: passwords may be set so that no unauthorised user can access the database, which may contain personal and sensitive data.

6. Query

   • A query specifies what records you are searching for and what fields from the records you would like to display.
     • Simple query search (keyword search) – looks for data in one field.
       • Complex query search – looks at data with multiple criteria.
   • You use wildcard searches in a query for data that you only know part of.

7. Security

   • If data is secure then it cannot
     • be destroyed
     • be accidentaly or maliciously altered
     • fall in to the hands of unauthorised people
   • Consequences of unsafe data
     • Loss of customers – unhappy customers go elsewhere
     • Payments for goods not being received
     • Bad publicity – all businesses rely on a good reputation
     • A number of methods are used to keep data secure
       • Locks on doors & Alarms
       • Biometric systems
   • Software methods for keeping data secure
     • Passwords
       • Authorised users are given a username. Each user also has a password that proves the user is really the one whose username is given. Using passwords is a method of authentication.
     • Access rights (file attributes) can be places on individual files
       • Read access (user can view file but not alter it) Write access (allowing the user to alter the contents of the file)
     • Back-ups
       • A back-up is a second copy of the data. If a problem arises with the data file, then the back-up copy is used.

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