Transcript chapter13
Chapter 13-1 Chapter 13 Data Modeling Introduction An Overview of Databases Steps in Creating a Database Using Rea Creating Database Tables and Records Chapter 13-2 Introduction Modern AISs use computers to systematically record data, in convenient and useful formats to provide easy access to required information. Chapter 13-3 An Overview of Databases A database is a collection of data that is stored in related files. Databases are important because they: contain valuable information, are very large in volume, store data in all its complexity have to maintain privacy contain irreplaceable data have to be complete, comprehensive, and accurate are priceless to Internet users Chapter 13-4 An Overview of Databases Question Which of these does not characterize a typical database? a. large number of records b. irreplaceable data c. high need for accuracy d. simple systems Chapter 13-5 Storing Data in Databases To be useful, the data in an organization’s databases must be stored and organized efficiently. The three important concepts are Chapter 13-6 Data hierarchy Record structures Record keys Data Hierarchy Storing accounting data in computer files involves organizing the data into a data hierarchy. The lowest level of information in a file is a binary digit or bit. Eight bits create a byte that represents a character. A data field combines several characters or bytes. A record combines related data fields. A set of records forms a file. A database is a collection of files that contain all the information for an application. Chapter 13-7 Data Hierarchy Question Which of these is not part of the ‘‘data hierarchy’’ (within the context of databases)? a. Record b. bit c. character d. data type Chapter 13-8 Record Structures and Record Keys The specific data fields in each record of a computer file are part of the record structure. Record Keys are identifiers for records: Primary keys are unique to each record Secondary keys are non-unique identifiers for records and used for searching files for specific information Foreign keys enable database records to reference one or more records in other files Chapter 13-9 Additional Database Concerns Administration Documentation Data integrity Processing Accuracy and Completeness Concurrency Backup and Security Chapter 13-10 Administration and Documentation A database administrator supervises the design, development, and installation of a large database system, and is responsible for its maintenance, security and revision Documentation involves descriptions of database structures, contents, security features, E-R diagrams, and password policies A data dictionary is a data file about data. Chapter 13-11 Data integrity Processing Accuracy and Completeness Data integrity controls are designed by the database developers and are customized for the application at hand. To achieve transaction controls database systems maintain an auditable log of transactions Chapter 13-12 Data integrity Processing Accuracy and Completeness can recover by verifying that a problem has happened, reversing whatever entries were made, and starting anew. In have the ability to audit any particular transaction to ensure processing accuracy and completeness. Chapter 13-13 Concurrency Backup and Security Concurrency controls are necessary to prevent multiple-user access to the same file execute transactions sequentially Information in many accounting databases must be protected is stored by backup procedures for retrieval is protected from unauthorized access by use of passwords encryption techniques Chapter 13-14 Concurrency Backup and Security Question Within the context of databases, the term ‘‘concurrency’’ refers to the possibility that a. a customer of one store might also be a customer of another store. b. two database users might want to access the same record at the same time. c. a credit entry for a customer requires a debit entry for a matching account. d. none of these Chapter 13-15 Steps in Creating Databases with REA An events-based accounting system (EBA) records activities that actually happen. The REA is a tool for designing databases. An AIS captures data about an organization’s resources, events and agents (REA). Chapter 13-16 Resources are an organization’s assets. Events are identifiable activities associated with a business processes. Agents are the people associated with business activities. Steps in Creating Databases with REA Question In the REA model, the ‘‘A’’ stands for: a. agents b. additions c. accounts d. associations Chapter 13-17 Steps in Creating Databases with REA The REA model requires the following steps: identify business and economic events, identify entities, identify relationships among entities, create Entity-Relationship diagrams, identify the attributes of data entities, and create database tables and records to validate the database. Chapter 13-18 Identify Events and Entities Business processes involve two types of events: economic events that impact an organization’s financial statements business events, that impact an organization in a value-added way Database entities include business and economic events information about the agents were involved in them the resources that events use or generate. Chapter 13-19 Identify Relationships Among Entities An entity-relationship (ER) diagram graphically depicts a database’s contents. An entity relationship may be direct relationship or indirect relationship ER diagrams depict entities being modeled and the relationships (cardinalities) among them. Chapter 13-20 Entity-Relationship Modeling The E-R model uses diamond symbols to represent relationships. include symbols (“1” or “*”) that provide information on cardinality. The cardinality of a relationship describes the number of occurrences of one entity that may be associated with a single occurrence of the other entity. Chapter 13-21 Cardinality Relationships Cardinality can be One-to-one (1:1) One-to-many (1:*), many-to-one (*:1), or Many-to-many (*:*) Cardinalities provide useful information about the nature of the company being modeled and the business policies that it follows. Chapter 13-22 Cardinality Relationships Question Which of these is not a cardinality between two database entities? a. one-to-one b. none-to-none c. one-to-many d. many-to-many Chapter 13-23 Organizing Database Records The structure of a database is a particular method used to organize records aims to develop this efficiently so that data can be accessed quickly and easily. The three types of structures are: hierarchical, network and relational. Chapter 13-24 Hierarchical Structures Accounting data are often organized in a hierarchy. A hierarchical structure has successive levels of data in an inverted treelike pattern, known as tree structures. Chapter 13-25 higher level records are parent records and lower level records are child records two records on same level are sibling records. Network Structures Databases can use a network structure to link related records together and capture many-to-many relationships. The linking is accomplished with pointer fields. The pointers maintain the data relationships. Chapter 13-26 Relational Structures Relational databases are more flexible. Users can define relationships when the database is created or at later points in time. Chapter 13-27 Creating Database Tables and Records An Introduction to Microsoft Access Creating Database Tables Creating Records Creating Database Relationships Guidelines for Creating Database Tables and Records Chapter 13-28 Microsoft Access and Database Tables Microsoft Access is a popular relational database used by many businesses and individuals used for small database applications Creating database tables requires three items: Field Name, names assigned to the data fields Data Type, to be specified for each data field Description Chapter 13-29 optional field that defines record structures Creating Records and Database Relationships Creating records individual records for the data fields Database relationships link tables together enable users to create multitable reports To create database relationships launch the relationships window, select tables, and link the tables. Chapter 13-30 Guidelines for Creating Database Tables and Records Some guidelines for creating database tables and records: Design first; create tables and records last. Name tables systematically and use conventional tbl prefixes. Use mnemonic names for data fields. Assign correct data types to data fields. Data fields that link tables must be the same data type. Limit the size of text data fields to reasonable lengths. Use input masks. Chapter 13-31 Copyright Copyright 2005 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make backup copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein. Chapter 13-32 Chapter 13 Chapter 13-33