Introduction to information systems T. Cornford, M. Shaikh is1 060 2013

syllabus, we only consider the relational model for design 
of a database although we do use an object oriented style of 
diagramming for undertaking analysis – see Chapter 8 of the 
subject guide for more detail.
Big enterprise scale databases can be centralised or distributed. That is, 
they can pull all the data together and store it in a single location. Users 

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then access it as they need to, probably by using networks. The alternative 
is to distribute the database. We could store, for example, all data relating 
to motor cars in England in one place, and all data relating to Scotland 
in another. Logically it might be one database, but operationally data is 
stored closer to where it is used. Software might take care of all this detail 
as seen by any user – in the case of photos stored on Picasa or Dropbox 
you and I have no idea where in the world they really are, or where there 
are backup copies of the photos! We just trust the service supplier. 
We may also choose to replicate a database, with a full copy of the 
database held in two or more locations. This could be a way to ensure 
security and integrity. If one datacentre is out of action, another is 
available, but there is the problem of ensuring that updates and changes 
made in one copy are reproduced on the others and that the copies remain 
synchronised. Again, software can help, but this is more complex to do and 
may at times fail.
4.7 Reminder of learning outcomes
Having completed this chapter, and the Essential reading and activities, 
you should be able to:
• express a logical understanding of how the technical parts of a 
computer-based information system work, their principal structures 
and components including contemporary software technologies for 
information processing and communications 
• demonstrate a good understanding of the significance of history for 
understanding contemporary information systems and the concept of 
legacy systems
• discuss the evolution of different types of information and 
communication technologies (eras) and the extent to which new 
technologies have led to changes in the way organisations use 
technology and are structured and operate 
• explain client–server, enterprise and cloud computing and give 
examples of each
• describe the database approach and offer examples of its advantages 
over a file-based approach.