Introduction to Database Chapter #9 Sec 9.1

What is a Database? A flat file is considered to be one-dimensional storage system because it presents its information from a single point of view. A flat file is considered to be one-dimensional storage system because it presents its information from a single point of view. A collection of data that is multidimensional in the sense that internal links between its entries make the information accessible from a variety of perspectives A collection of data that is multidimensional in the sense that internal links between its entries make the information accessible from a variety of perspectives

Figure 9.1 A file versus a database organization

Drawbacks of File system Different departments such as Customer Service Department and Payroll Department were no able to share information so the same data was duplicated in various departments Different departments such as Customer Service Department and Payroll Department were no able to share information so the same data was duplicated in various departments Secondly when an employee moved his record was deleted from all the places in which many errors were possible Secondly when an employee moved his record was deleted from all the places in which many errors were possible

Advantage of Database If data is integrated at one place then each department can share that data. If data is integrated at one place then each department can share that data. Control of data is concentrated in the administrative position called Database Administrator (DBA) Control of data is concentrated in the administrative position called Database Administrator (DBA) Thus this centralized data helps in important decision making regarding the entire organization. Thus this centralized data helps in important decision making regarding the entire organization.

Disadvantages One concern is the control of access to sensitive data. For example someone working on organizations newsletter might need access to employee names and addresses but should not have access to employee payroll data. Thus the ability to control data access is important One concern is the control of access to sensitive data. For example someone working on organizations newsletter might need access to employee names and addresses but should not have access to employee payroll data. Thus the ability to control data access is important To provide data privileges database relies on schemas and sub schemas To provide data privileges database relies on schemas and sub schemas

9-7 Schemas Schema: A description of the structure of an entire database, used by database software to maintain the database Schema: A description of the structure of an entire database, used by database software to maintain the database Subschema: A description of only that portion of the database pertinent to a particular user’s needs, used to prevent sensitive data from being accessed by unauthorized personnel Subschema: A description of only that portion of the database pertinent to a particular user’s needs, used to prevent sensitive data from being accessed by unauthorized personnel

Example Suppose a schema for university database indicates that each student record contains items such as name, address, phone number, academic record etc. Moreover student and faculty are linked in the form that each student has a faculty advisor. Suppose a schema for university database indicates that each student record contains items such as name, address, phone number, academic record etc. Moreover student and faculty are linked in the form that each student has a faculty advisor. Now the universities registrar would have a sub schema view in which he is able to see the faculties supervising students but should not be able to see the past employment history of the faculty member Now the universities registrar would have a sub schema view in which he is able to see the faculties supervising students but should not be able to see the past employment history of the faculty member

Figure 9.2 The conceptual layers of a database implementation