23-01-2013, 10:19 AM
INTRODUCTION, DATABASE CONCEPTS AND ARCHITECTURE
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OBJECTIVES
By the end of this unit students will understand:
what a database and database management system are
the importance of information as a strategic resource within an organisation
how database systems differ from earlier file processing techniques
the role of various types of users involved with the design, implementation and maintenance of a medium sized or large database application
the notion of data independence
the 3-level architecture of database management systems and how it provides for data independence
the different levels of abstraction used in database systems.
INSTRUCTIONS
You should read Chapters 1 and 2 of the ElMasri and Navathe text first, then study this unit and complete all the SAQs. Finally, you should complete the exercises given at the ends of Chapters 1 and 2 of the text.
INTRODUCTION
All large organisations today – banks, insurance companies, public utilities (e.g. ESB, Eircom) hospitals, etc. – are computerised. Much of their routine information processing such as sending out bank statements, billing etc. is performed by computer. In some cases the data is entered manually, such as when you use an automated teller machine (ATM) such as a Banklink or Pass machine. You key in the amount of money you wish to withdraw and the computer updates your account details and gives you the money. In other cases, the data is input automatically. One example of automatic data entry is the stock control system in supermarkets which receives input directly from the laser scanners at the checkouts. When the bar codes on your groceries are scanned by the laser, not only is a bill produced, but the details of the items you have bought are recorded on the stock control system. Such an automatic system has many benefits, both for the customer and for the supermarket. As a customer, you get a fully itemised bill, which is more accurate and informative than when prices had to be entered manually into the conventional cash register. From the supermarket’s point of view, there is no need for staff to count the number of pounds of butter, or pots of jam, or packets of biscuits left on the shelf. The computer system provides them with a very accurate picture of what is supposed to be in stock and what is out of stock.
CASE STUDY: TRANSLATORSFORYOU.COM
Consider a company that offers translation services over the web. Translation jobs are submitted to TranslatorsForYou.com by registered customers. The company has a team of translators who pick translation jobs from a list, carry out the translation and return the translated text to the company. Once the translation has been approved (by the company or by the customer), the customer is charged for the job and provided with the translation, and the translator is due his/her fee.
The TranslatorsForYou web site allows:
users to register as customers
registered customers to submit jobs,
customers and translators to view outstanding/unassigned jobs,
translators to take on an outstanding/unassigned job,
translators to submit completed translations, and
customers or company personnel to review and approve translations.
In addition, internal applications allow for registration of translators, charging of customers, and payments to translators. Company staff will also need to be able to oversee translators’ work, check that jobs are being handled in a timely fashion, and so on.
This brief description of a web translation service is greatly simplified – it ignores payment records, it doesn’t allow customer to choose a translator – but it will serve our purposes for now.
The company’s website and accounting applications depend on a database to store details of translators, customers, translation jobs, completed translations, etc. Translators, jobs, etc, are examples of real-world entities in our example. An entity is an object about which we wish to store information in the database. These entities are linked together by relationships.
INFORMATION AS A RESOURCE
At the beginning of this unit, we stated that most large organisations today use computerised information systems in their day to day operations. Not only do they use them routinely, but they have also grown critically dependent upon them. For example, imagine trying to book a seat on an aeroplane today if the computerised Passenger Seat Reservation System wasn’t working. Automated checkouts using laser scanning of bar codes in supermarkets and bank ATMs would not exist without a computer. It is not, of course, sufficient for the computer to simply be operational to support these applications; the computer must also operate correctly otherwise flights could be overbooked, resulting in a lot of angry passengers and consequent loss of commercial advantage. I don’t suppose any of us would complain if the ATM gave us too much money, but, if it gave us too little we would not be too pleased!
Malfunctioning, inaccurate, unreliable information systems can therefore severely affect the profitability and commercial viability of organisations. This illustrates clearly the importance of (computerised) information as a strategic organisational resource. In the past, large organisations have had no problem seeing personnel, plant and buildings as important quantifiable resources. Personnel cost money, in terms of both training and salaries and the company cannot exist without them. Money is also invested in plant and buildings. A manufacturing company cannot manufacture goods without the necessary machinery and raw materials. Information, on the other hand, is a much less tangible, but no less critical, resource.