Databases

Databases

1. Databases general information

   • What is a database
     • A database is a persistent organised store of data on a computer system
     • Persistent - it's saved on a secondary storage for the future
     • Organised - databases have a structure so they can easily be processed
   • The importance of databases
     • Most organisations need their database to operate properly
     • A database needs to be accurate, up to date, available to those who need to use them and protected from those who shouldn't have access
     • Database administrators go to great lengths in order to protect their data against errors, loss, insufficient dat, inconsistencies, unauthorised access
     • Errors in databases could result in "embarrassment " such as sending the wrong bill to a customer, financial loss, life or death situations such as incorrect navigational data for an aircraft
     • DBMS
   • Where are databases
     • Databases tend to be in every organisation there is.
     • Databases affect most aspects of our lives. Everyone has details about themselves stored on many databases
     • Database models are the structure of the database
       • Flat file
         • This is the most basic database this consist of rows and records
       • Hierarchical
         • The hierarchical model is sometimes useful when making an inventory. Some parts of stock items might always belong with other
       • Relational
         • They are the most useful and common
         • They store separate tables and then linked together
         • Each table has data about an entity. An entity is something in real life that would store data.
   • database operations
     • Administrators of databases help create and maintain databases
     • The help organisations to process information . They make it easier to access, search,sort, rout, copy, protect
     • A subset of data is called a view. Making suitable views for each staff member increases the efficiency of using the database and reduces risks
     • Standard operations are sometimes listed under the term CRUD Create, Read, Update, Delete
     • Data matching compares different databases to look for particular relationships
     • Data mining is a process that looks in many different unrelated databases. This shows unexpected relationships that may not have been noticed before
   • Data types
     • Number
     • Text
     • Number currency
     • Date/time
     • Yes/no Boolean
   • security, integrity, validation and verification
     • Data security means t keep the data safe. if data is lost this could damage the company associated with it
       • data could be lost because of a catastrophe, an accident or a malicious action
       • this is prevented by making regular back ups, having a mirror database somewhere else, restricting access
     • Data Integrity means that the data reflects the reality. it implies that the data is correct and fit for its purpose
     • Validation
       • length check
         • must have a certain amount of characters can be above or below a limit
       • type check
         • must be a certain data type
       • range check
         • must fall between certain limits
       • presence check
         • must be filled in
       • lookup check
         • must match whats held on file
       • format check
         • must conform to a certain pattern
       • check digit
         • must be exactly he same as data previously entered
     • Verification
       • this is to check that all data inputted is correct