Database system developed because of the need to store large amount of data and retrieve that data quickly and accurately for example, a University abrary stores details about the books held and loans taken out by student. Not very long ago this information about the books and loads might have been stored in a box card index, nowadays, only a few decades later, student are able to view their loans online and see if a book is available and reserve it. The abrary staff can quickly access statistics on overdue books, popular books which never have the shelves.
Another example is a company that accepts customer orders for instance, orders for spare parts for electrical goods. Originally orders might have been created when a customer telephone the company to place the order. If information about the customer already existed in a paper file then his/her details would be requested and recorded. An order form would have been filled in and copies: one copy being stored in a filing cabinet, the other, information on stock held would need to be accessed.
Eventually, the order entry system was computerized so that by the 1960’s the data about customers and orders might have been stored in a computer file- a magnetic tape file and then later magnetic desk. These files were processed by computer programs. Other applications programs were used which could create invoices, orders to suppliers and so on. Although different application software would at times require similar data, the data would be kept on different files. In both types of system, the paper one and the files system, processing was slow and problems of inconsistencies of data could easily develop. The introduction of shaved files. Whereby different applications shaved some of the same files, solved some of the problems described earlier, and was good for providing routine data. For example, a customer order application and an invoicing application might use both the customer and stock files, and ind addition their own files. As only one copy of each file was made available, the inconsisitencies were avoided. However, this method was not efficeient, as a share file would only be available to one application at a time. Share files systems were also not effective in providing data for planning and control of an organization.
In the 1960’s database systems began to emerge with the release of the IBM production IMS, a system where the user viewed the data as a hierarchical tree. In the late sixties, database systems based on a different data model where developed. This time the user view of the data was a network of data recorded. In both cases skilled programmers were required and users tended to be large organizations. The database approach was an improvement on the share file solution as the software which was used to control the data was quite powerful. The software consisted of a number of components which provided facilities for acquiring data, data security and integrity and the ability to access the data simultaneously by different users.
Another character of database systems is that the underlying structure of the data is isolated from the actual data itself. The specification of the entire database is called Schema. There are various level of Schema- the conceptual schema or model is discussed below. If there is a requirement to change the structure of the data, the change will be made at the schema level. Such changes are independent of both the physical storage level and the level seen by individual users.
Returning to our brief history, by the 1970’s the study of database systems had become a major academic and research area. The relational model was first proposed in 1970 by Ted Codd with his services of pioneering papers. The theory underpinning relational database is derived from the mathematical principles of set theory and predicate logic. The model is based on the familiar concepts of table,...
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