Chapter 4 Relational Databases Dr.Mohamed Mousa

Files versus Databases ? File: Contain data about one entity from a record. Database: A set of interrelated , centrally coordinated data files that are stored with as little data redundancy as possible , to provide relevant information to the users. Dr . Mohamed Mousa

Databases’ characteristics : Integration. Independency. Relevancy. Precision. Timely manner. Dr . Mohamed Mousa

Advantages of Database Systems: Data Integration Files are logically combined and made accessible to various systems. Data Sharing With data in one place it is more easily accessed by authorized users. Data Inconsistency Eliminates the same data being stored in multiple files, thus reducing inconsistency in multiple versions of the same data. Data Independence Data is separate from the programs that access it. Changes can be made to the data without necessitating a change in the programs and vice versa. Cross-Functional Analysis Relationships between data from various organizational departments can be more easily combined. Dr . Mohamed Mousa

Hierarchical Databases . Networked Databases. Relational Database. Types of Databases : Hierarchical Databases . Networked Databases. Relational Database. Dr . Mohamed Mousa

Hierarchical Databases: A base that collect and save data in the form of a relationship between father and sons (and always start from top to bottom) , and is characterized by easy usage and frequent prevalence. Dr . Mohamed Mousa

Networked Databases: A base that collect and save data in the form of mutual and overlapping relationships between files and each other, and fit a large-sized companies. Lecturer 1 Lecturer 2 Lecturer3 Section 3 Section 1 Section 2 Dr . Mohamed Mousa

Relational Database: Relational data model represents the conceptual and external level schemas as if data are stored in tables. Dr . Mohamed Mousa

Design Requirements for Relational D.B Every column must be single valued. Primary keys must contain data (not null). Foreign keys must contain the same data as the primary key in another table. All other attributes must identify a characteristic of the table identified by the primary key. Dr . Mohamed Mousa

Dr . Mohamed Mousa

The idea of the session : $30,000 / 65% = $46,154 To check, go through the formulas for breakeven plus target profit: $66,154/$250 = 265 units 265 x $250 = $66,250 Differences due to rounding. Dr . Mohamed Mousa

Self training ….. List three examples from you that illustrate the types of databases, explaining the structure of each. Dr . Mohamed Mousa