H Database example essay topic

Database DesignScenarioCurrently a school uses a non-computerized database system to store the following information about its students: roll class, surname, first name, guardian's name, address, student's date of birth, gender, sport house, emergency-contact telephone number, mailing name, list of subjects offered, and subjects in which the student is enrolled. The system takes up a large amount of space, has many duplicated entries some of these with mistakes and it is time consuming to search. The school intends to introduce a relational-database management system to overcome these problems. Current school data storage and retrieval system (the pre-computer database system) "h School staff, teachers and office staff are the users of the database". h Database used to track all details of students in the school". h Large amounts of data are stored. An individual record is required for each student. "h Lots of duplication exists as details of subjects offered by the school are duplicated on individual student records". h Data is organised in alphabetical order on student names within years". h Data is stored in a number of filing cabinets. Advantages"h quick to find details of a student if year and surname are known"h data is stored in a central secure location"h original source material is stored in the student file.

Disadvantages"h slow to find details of students when surname and year are not known"h data storage takes up a lot of room"h minimal number of staff can access records at one time"h data is duplicated. Stages of development of the computerized relational database system The new computerized relational database system will be developed in the following stages:" h analysis"h design"h implementation"h maintenanceAnalysisIn this stage the current system is analysed to determine the functions it performs and those that it is unable to perform. Direct and indirect users of the new system are interviewed to determine what they require from the new system. The inputs to the new system, the processes it is to perform and the outputs from the system are clearly defined. A recommendation is made about the type of new system that will be required to meet the identified needs. During the analysis stage, the following is determined:" h current storage space of student records needs to decrease"h an easily update-able backup of student records is required, "h one staff member is to be responsible for the administration of the system, "h unnecessary duplication of data is to be avoided, "h all teaching staff, office staff and the Principal need to have access to the database simultaneously - read access only is required "h reports such as roll class lists, subject class lists, lists of sporting houses, student contact details and family mailing lists need to be easily generated.

To meet these requirements, a relational database system has been recommended. A relational database is 'a database in which data is organised in a series of relationships, or two-dimensional tables, where the columns (attributes) represent data fields, and the rows (tuples) represent records. Linking of data between records in different files is done by means of a key field. ' The relational model was chosen in preference to a flat file system as the requirements of users would not be met with a flat file. A flat file is 'a type of database where all of the data is contained in one file'. For all of the information to be held in one table, every student record would require data to be unnecessarily duplicated, introducing redundant data.

For example, every student record would require information about the subjects the student is enrolled in and these subject details would be duplicated throughout the flat file. This duplicated data increases the space required by the computer system to process and store the data. It also leads to possible problems with the integrity of the data when modifications to this duplicated data is required. Design In this stage the relational database system is developed. The system is made up of two parts, the database management system and the database. A database management system (DBMS) is 'the software that builds, maintains and provides access to a database.

It also provides data dictionary facilities, file protection and security against unauthorised use'. Relational database management systems include software packages such as Microsoft Access. These packages provide the frame work to allow the tables to be developed and linked. A database is defined as 'an organised collection of data items which may be accessed by a database management system.

The database may consist of several linked files'. The school database will consist of a number of tables that hold information on students and related material. The information to be stored on students; roll class, surname, first name, guardian's name, address, student's date of birth, gender, sport house, emergency-contact telephone number, mailing name, list of subjects offered, and subjects in which the student is enrolled will be held in the following tables:" h roll class"h sports house "h students"h subjects enrolled"h subjects offered"h contact details The diagram below shows a schema for this database using the tables outlined above. A schema is defined as 'An organised plan of the entire database showing how and where the data is to be found, descriptions of the data, and their logical relationships. The schema is produced by the database designer and is maintained by the database administrator. ' The schema shows a list of the attributes (column / field headings) for each table.

The schema above has a primary key for each table. The primary key is defined as 'a character or group of characters used to identify a unique record in a database!" . The key is composed of one or more fields from the record. Also known as primary key. Examples of primary keys could be ID number, part number, payroll number, etc. ' The primary key field in each list is one field.

The exception is the 'Subjects Enrolled' table. This table is made up of two keys from other tables. Individual tuples in this table will be unique combinations of Student ID and Subject Code. This table is used as a link between the 'Students' table with the 'Subjects Offered' table because there is no other logical way of linking the data without creating redundant entries. The large table beginning with Student ID and First Name contains foreign keys from the other tables. These foreign keys are Contact ID, Roll Code and House Code.

(Note! V Roll Code and Roll Class Code are the same attribute. They have been incorrectly typed in the diagrams, but they must be the named same before the relationships can function correctly. ).