A backup is a copy of a system that is available in case someone wants a copy of a file that they deleted or in case the whole system crashes and has to be restored from a backup copy. Backups are kept in 'online storage' so they are easily accessible.
An archive is a copy of files that is kept offline as a historical record and is not available for updating files or restoring a system.
Data integrity is about ensuring that data is correct. Data might be wrong on input; or it may be corrupted accidentally by hardware failure or deliberately by a hacker. Data must be accurate and reliable or else it isn't any use. Validation and verification are used to ensure that data are correct when entered.
Data security is concerned with keeping data safe from events such as theft, damage, flood or fire.
Verification means checking that data are input correctly, for example copied from a source document such as an application form. One simple way to verify data is to enter it twice and compare the two versions. Note that verified data may still be incorrect if the source was incorrect.
Validation means checking that data is within a specified range of values e.g. between 1 and 10 or that a date is valid. Just because data are valid does not mean they are correct.
Validation checks include:
Errors include: copying wrongly, entering data twice, omitting data, transposition, typing errors
Batch processing is where data are collected and processed together as a batch. This often happens overnight, for example a holiday company might collect bookings during the day's trading and uploaded to the company mainframe overnight. This used to be done a lot more before computer technology advanced to its current state, for example transactions at the branch of a bank would be stored locally and then uploaded at night.
On-line processing is where data are updated almost immediately, for example in internet banking where the user can manipulate the contents of an account and the changes take place within a matter of seconds.
Real-time processing is where the response of the computer is so fast that there appears to be no time lag between the input of the data and the response of the computer. An example of this is in aircraft control systems where inputs from sensors in the aircraft cause changes in the ailerons and rudder to keep the aeroplane flying correctly. Without real-time, immediate response from the computer the aeroplane would not stay in the air. Another example is ABS braking systems where the brakes and steering must respond very quickly to the message that the car is out of control.
Off-line processing means that you are not connected to the computer where the data will be processed. For example, teachers can take their reports home using a 'briefcase' facility that stores all the data they need; when they next come to school they upload their briefcase to the computer system and the reports are copied into the correct place.
A system is a way of doing something in an ordered way, for example processing an application for insurance or collecting readings from gas or electricity meters. Systems eventually need replacing because they cannot cope with changes in the volume of data or changes in the way data are processed or changes in software and computer hardware. Computer systems in rapidly changing organisations may last less than a year before they are replaced.
When a system is to be replaced a new one is considered in a structured way using the techniques of systems analysis. This involves these stages:
A new system must have documentation for users so that they can learn how to use it and for technical staff so they can fix or improve it.
The Analysis stage of systems analysis includes these techniques:
Inputs are generally collected with forms, either on paper or on screen. Forms should be easy for those filling them in to understand. The data areas should be organised neatly so that the data is entered in a logical sequence.
Data are stored in files or databases. File are organised around records and records consist of fields. Fields hold data such as name and date of birth. Records contain groups of fields that are all facts about an object such as a person or a car. Files consist of many records, for example customers at a bank.
Databases store their data in tables, which are very similar to files. A table holds many records and each record contains a number of fields about something like a car or a person. A database may contain many tables. A database like MS Access includes a way of designing tables, either in 'design view' or with a 'wizard'.
One form of output is the report in a database management system. Another form of output is a mail merge document.
A system may be implemented directly, overnight, whereby the staff come in next day to find that a new system has entirely replaced the old one.
Alternatively, a new system may be phased, brought in over a number of weeks, often across different departments.
Another way of introducing a new system is the 'parallel' approach where the old and new systems are run together for a short period. This gives the organisation a chance to see if the new system is working properly while still having the 'safety net' of the old system to fall back on if things go wrong.
Another way of introducing a new system is to have a pilot of the new system in one part of an organisation and then, if successful, introduce it to the other departments.
Staff will need training in the new system so that they are fully prepared for it.
Also called knowledge-based systems. The aim of these systems is to capture the knowledge of experts into a computer. Knowledge is a series of facts that can be interpreted by a computer program to answer questions that are not simply factual but also involve judgement. An expert, such as a doctor, a lawyer or a teacher makes a judgement based on experience and knowledge gained through their professional duties. This type of knowledge is very different to the kind of structured facts found in databases. A database will answer questions like 'Find all the Ford Fiestas coloured red that are less than £2000'; an expert system would answer a question like 'why doesn't my car work?'.
An expert system is created by collecting answers to questions in a field of knowledge such as medicine, cookery or engineering. The first thing is to define the purpose of the expert system, what questions it will answer. Then facts are collected from experts for entry into the 'knowledge base'. The knowledge base is structured so that it will provide answers to questions in a structured way. The knowledge base is a set of facts or statements, to which rules are added to allow conclusions to be drawn. For example, John and Mary have the same mother so it can be concluded from a simple rule that they are siblings; if they have different fathers then another rule would conclude that they are half-brother and sister.
Next, choose a software tool to implement the system. This will provide a way of displaying questions to the user such as 'is the engine running?' or 'does it have feathers?' The user interface should provide a way of entering answers to these questions.
Implement and test the system, create documentation, train users.
Mail merge allows data in databases to be merged with a document to produce something like a personalised letter to lots of different people and address labels.