Before the advent of computers, information files had to be maintained manually, with paper-based files kept on index cards stored alphabetically in boxes or drawers or file cabinets. With the creation of database software, files can now be manipu- lated by the computer, thus saving hours of physical labor in handling, updating, and moving information when changes are made. (See Figure 2.3.)
|FIGURE 2.3 | Database fundamentals.
Database software enables users to create new files; add, delete, or change entries in files; perform limited calculations using data; sort records according to varying criteria; and merge two or more files into one.
To create, test, and manage a successful database, it is necessary to have a thorough understanding of the data to be stored, the reason for their existence, and how they can be managed to provide the desired end product. Based on the type of information to be stored, three types of database structures are available: hierarchical, network, and relational.
Hierarchical Databases. The simplest database is the hierarchical, or tree-structured, model in which information is accessed from the top down. For example, a social security number may be used to identify a record followed by a student’s name and address. If the user wants to search the records and knows only a student’s name, the system must follow the hierarchical path. This method is said to be a parent–child relationship; that is, each item relates only to the one above and below it in the hierarchy.
Network Databases. Network databases allow multiple, explicit relationships to exist, rather than only top-to-bottom relationships. The network model also uses a less rigid search structure. The shortest distance to the required information is followed, rather than a top-to-bottom route. The complexity of this system makes modification a more involved procedure.
This model works well for standardized operations wherein transactions predictably follow a preconceived path for each occurrence, such as banking transactions, airline reservations systems, and inventory control.
Relational Databases. A relational model allows multiple associations among common fields in more than one database. Relational databases are arranged in table format, two-dimensionally, with rows and columns. What was referred to in the previous two models as a file is now a relation. A record is now termed a row; a field is now a column. In order to avoid confusion, we will continue to refer to files, records, and fields throughout this description. The relational database performs three basic functions:
Joining. Two files are merged into one.
Projection. Fields are extracted from various files to form a new file.
Selection. Various records may be chosen according to the user’s own criteria; this is called selection.
Databases in Education
The educational community has been a beneficiary of the database’s ability to com- pile, store, and manipulate huge amounts of demographic and statistical informa- tion. For example, once student records are entered into a database, they can be accessed by any criteria the user wishes and compiled to generate specific and indi- vidually designed reports. School districts and universities have built databases to handle student files, which can include currently enrolled students, classes, financial accounts, grades, and schedules.
A relational database is useful for data such as school records. Student information, course information, class information, and instructor information can all be stored in a database, and grades can be maintained, averaged, compared, printed, and mailed to students. Libraries are another area in which relational databases are used so that resources can be accessed according to the interest of the user.
|Common commands and operations associated with most database programs:
Edit. The Edit command is used to change or modify data that are already part of a file. The system displays the entire record and fields can be altered as necessary. Entered changes replace the earlier entries.
Enter. When the user chooses the Enter command, a new record is created and stored in the file.
Field. A field is a category of information. Multiple fields make up a single record.
File. A group of related records is called a file.
Form. Forms can be created to assist entry and viewing of data. Forms contain input areas based on the database fields.
Query. Running a query allows the user to select only certain records within a file based on a set of criteria. For example, a principal may want to generate a mailing list of parents of a specified segment of the student population; however, the database files contain addresses of parents of all the students. A query can be used to search for only the specified parents.
Record. A record is the basic unit of database organization. The information for each person in a contact database, for example, would be a separate record.
Report. Once a query has been run, the selected data can be displayed and printed in a formatted report.
Sort. The user can reorder records by performing a sort based on any one field of a record. For example, student records might be arranged alphabetically according to students’ names or numerically according to zip codes for mailing purposes. Sorting can be done in ascending or descending order according to the chosen field.
Databases are also an invaluable new tool for the classroom teacher. A database can be created for members of an individual class and used to arrange information, as the teacher requires. Curriculum enhancements are available through library data- bases and other sources of reference materials. By implementing a database search for content-relevant information, a teacher can locate multiple sources of material in much less time than that required for a physical library search. Educators and stu- dents should be aware of the use of databases in other sectors of society; informa- tion from online databases frequently can be accessed for educational purposes. Government agencies, nonprofit organizations, businesses, and private individuals all store information in databases.
|How Does This Look In The Classroom?