Databases

(*D*ata*B*ase *M*anagement *S*ystem) Software that controls the organization, storage, retrieval, security and integrity of data in a database. It accepts requests from the application and instructs the operating system to transfer the appropriate data. The major DBMS vendors are Oracle, IBM, Microsoft and Sybase. MySQL is a very popular open source product.

DBMSs may work with traditional programming languages (COBOL, C, etc.) or they may include their own programming language for application development.

DBMSs let information systems be changed more easily as the organization's requirements change. New categories of data can be added to the database without disruption to the existing system. Adding a field to a record does not require changing any of the programs that do not use the data in that new field.

*Major Features of a DBMS

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*Data Security*

The DBMS can prevent unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or a subset of it known as a "subschema." For example, in an employee database, some users may be able to view salaries while others may view only work history and medical data.

*Data Integrity*

The DBMS can ensure that no more than one user can update the same record at the same time. It can keep duplicate records out of the database; for example, no two customers with the same customer number can be entered.

*Interactive Query*

Most DBMSs provide query languages and report writers that let users interactively interrogate the database and analyze its data. This important feature gives users access to all management information as needed.

*Interactive Data Entry and Updating*

Many DBMSs provide a way to interactively enter and edit data, allowing you to manage your own files and databases. However, interactive operation does not leave an audit trail and does not provide the controls necessary in a large organization. These controls must be programmed into the data entry and update programs of the application.

This is a common misconception about desktop computer DBMSs. Complex business systems can be developed, but not without programming. This is not the same as creating lists of data for your own record keeping.

*Data Independence*

With DBMSs, the details of the data structure are not stated in each application program. The program asks the DBMS for data by field name; for example, a coded equivalent of "give me customer name and balance due" would be sent to the DBMS. Without a DBMS, the programmer must reserve space for the full structure of the record in the program. Any change in data structure requires changing all application programs.

*Database Design

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A business information system is made up of subjects (customers, employees, vendors, etc.) and activities (orders, payments, purchases, etc.). Database design is the process of organizing this data into related record types. The DBMS that is chosen is the one that can support the organization's data structure while efficiently processing the transaction volume.

Organizations may use one kind of DBMS for daily transaction processing and then move the detail to another DBMS better suited for random inquiries and analysis.

Overall systems design decisions are performed by data administrators and systems analysts. Detailed database design is performed by database administrators.

*Hierarchial, Network & Relational

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Information systems are made up of related files: customers and orders, vendors and purchases,