Rdbms Notes

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INTRODUCTION:DATA :- Data is a collection of facts, which is in unorganized but they can be organized into useful form. Data is of two types :1.Raw Data :- It is a Data which are collected from different sources and has no meaning. ` 2. Derived Data :- It is a data that are extracted from Raw Data and used for getting useful information. Derived Data is called as INPUTDATA. INPUT DATA is processed to get the OUTPUT data. The OUTPUT DATA is called as INFORMATION. The database today may contain either data or information. The term data and information are closely related.

Proccessing of data is called Data Proccessing. Proccessing of Data in an electronic
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3. End users: - End Users are the persons, whose jobs require access to the database for quering, updating, and generating reports. 4. System Analysts and Application Programmers: - Systems analysts determine the requirements of end users, and develop specifications for canned transactions that meet these requirements. DATA MODELS: - The structure of a database is the concept of a data model, a collection of conceptual tools for describing data, data relationships, data semantics and consistency constraints. 1. Network data Model 2. Hierarchical data model 3. Relation data model Network data model: - data in the network model are represented by collection of records and relationships among data are represented ny links. The links can be



viewed as pointers. The records in the database are organised as collections of arbitrary graphs. Hierarchical Data Model :The hierarchical model is similar to the network model in the sence that data and relationships among data are represented by records and links respectively. It differs from the network model in that the records are organised as collection of trees rather than arbitrary graphs. Relational Model:- The relational model represents data and relationships among data by a collection of tables.each of which has a columns with unique names.The following relational database showing Customers and Accounts they have. From the above CUSTOMER and ACCOUNT
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