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This 4 page Class Notes was uploaded by Adriana on Saturday January 30, 2016. The Class Notes belongs to CIT 241 at Pace University taught by Coakley in Spring 2016. Since its upload, it has received 29 views. For similar materials see Database Management in Information technology at Pace University.
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Date Created: 01/30/16
Relational Databases Purpose of a Database to keep track of things Unlike a list or spreadsheet, a database may store information that is more complicated than a simple list Problems with Lists: Redundancy In a list each row is intended to stand on its own. As a result the same information may be entered several time. Multiple Themes In a list, each row may contain information on more than one theme. As a result, needed information may appear in the lists only if information on other themes is also present List Modification Issues Redundancy and multiple themes create modification problems: o Deletion problems o Update problems o Insertion problems Relational Databases A relational database stores information in tables. Each informational topic s stored in its own table. In essence, a relational database will break up a list into several parts - one for each theme in the list. Relational Databases segment information by themes. Putting Pieces Back Together In our relational database, a list is broken into several tables. Somehow the table must be joined back together In a relational database, tables are joined together using the value of the data If a PROJECT has a CUSTOMER, the CUSTOMER_ID is stored as a column in the PROJECT table. The value stored in this column can be used to retrieve specific customer information from the CUSTOMER table. Customer Project Customer_ID 001 Project_ID 001 Customer Name Customer_ID 001 Structured Query Language (SQL) An international standard for creating, processing, and querying databases and their tables. Many database applications use SQL to retrieve, format, report, insert, delete, and/or modify data for users SELECT * From tblCUSTOMER Where Customer_Last 'Smith' The 4 components of a database system are: Users Database Application Database Management System (DBMS) Database A user of a database system will: Use a database application to track things Use forms to enter, read, delete, and query data Produce reports Components of a Database System A user of a database system will: Use a database application to track things Use forms to enter, read, delete, and query data Produce reports The Database A database is a self-describing collection of related records. The database itself contains the definition of its structure. Metadata is data describing the structure of the database data. Tables within a relational database are related to each other. DBMS Serves as an intermediary between database applications and the database Manages and controls database activities It creates, processes and administers the databases it controls Functions Create databases, tables, supporting structures Read database data Modify database data (insert, update, and delete) Maintain database structures Enforce rules Control concurrency (several computations are executing simultaneously, and potentially interacting with each other) Provide security Perform backup and restore Example Database Metadata: A Relationship Diagram Database Contents User data Metadata Indexes and other overhead data Application metadata Personal Database Systems Have one application Have only a few tables Are simple in design Involve only one computer Support one user at a time Microsoft Access is often used for this Database Application and DBMS are connected Database Application A set of one or more computer programs that serves as an intermediary between the user and the DBMS. Functions Create and process forms Process user queries Create and process reports Execute application logic Control database applications *Referential Integrity Constraints ensure the values of a column in one table are valid based on the values in another table A customer makes an order. Their customerID is in the CUSTOMER table and their order is in the ORDER table. You must have both values existing in their appropriate tables. SQL Syntax Table names: all caps Column Name: First letter cap, rest lowercase
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