Kế toán kiểm toán - Chapter 4: Relational databases

Accounting Information Systems9th EditionMarshall B. Romney Paul John Steinbart4-1©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartRelational DatabasesChapter 44-2©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLearning ObjectivesExplain the difference between database and file-based legacy systems.Describe what a relational database is and how it organizes data.Explain the difference between logical and physical views of a database.Create a set of well-structured tables to properly store data in a relational database.3©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartIntroduction Ashton Fleming, the accountant for S&S, believes that the best way to provide Susan Gonzalez and Scott Parry with easy access to the information they need to run their business is to build S&S’s new AIS as a database system.4©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartIntroductionAshton decides to prepare a brief report for them addressing the following questions:What is a database system?What is a relational database system?How do you design a relational database?5©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartIntroductionThis chapter explains what a database is and how it differs from a file-oriented system.It also describes the structure of a relational database system.The chapter concludes by discussing the basic steps involved in designing a database.6©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLearning Objective 1Explain the difference between database and file-based legacy systems.7©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartTypes of FilesTwo basic types of files are used to store data.The master file, which is conceptually similar to a ledger in a manual system.The transaction file, which is conceptually similar to a journal in a manual system.8©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartFile ApproachFor many years, companies created new files and programs each time an information need arose.This proliferation of master files created problems:Often the same data was stored in two or more separate files.The specific data values stored in the different files were not always consistent.9©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartFile-Oriented ApproachShipping ProgramSalesProgramFile 1Fact A Fact B Fact CFile 2Fact B Fact D Fact EBillingProgramFile 3Fact A Fact G Fact E10©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDatabasesThe database approach views data as an organizational resource that should be used by, and managed for, the entire organization, not just the originating department or function.Its focus is data integration and data sharing.Integration is achieved by combining master files into larger pools of data that can be accessed by many application programs.11©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDatabasesDatabase management system (DBMS) is the program that manages and controls access to the database.Database system is the combination of the database, the DBMS, and the application program that uses the database.Database administrator (DBA) is the person responsible for the database.12©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDatabase ApproachBilling ProgramShippingProgramDatabasemanagementsystemSales ProgramFact A Fact B Fact C Fact D Fact EDatabase13©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLearning Objective 2 Describe what a relational database is and how it organizes data.14©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartRelational DatabasesA data model is an abstract representation of the contents of a database.The relational data model represents everything in the database as being stored in the form of tables.Technically, these tables are called relations.15©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartRelational DatabasesEach row in a relation, called a tuple, contains data about a specific occurrence of the type of entity represented by that table.16©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLearning Objective 3Explain the difference between logical and physical views of a database.17©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLogical and PhysicalViews of DataA major advantage of database systems over file-oriented systems is that the database systems separate the logical and physical view of data.What is the logical view?It is how the user or programmer conceptually organizes and understands the data.18©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLogical and PhysicalViews of DataWhat is the physical view?It refers to how and where the data are physically arranged and stored on disk, tape, CD-ROM, or other media.The DBMS controls the database so that users can access, query, or update it without reference to how or where the data are physically stored.19©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLogical and PhysicalViews of DataLogical View User ALogical View User BPast Due AccountsName Balance DaysJackson 2145 48Houston 1595 65October Sales by RegionOperatingsystemDBMSDatabase20©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLogical and PhysicalViews of Data Program-data independence is the separation of the logical and physical views of data.21©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartSchemasA schema describes the logical structure of a database.There are three levels of schemas:Conceptual-level schemaExternal-level schemaInternal-level schema22©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartSchemasThe conceptual-level schema is an organization-wide view of the entire database.The external-level schema consists of a set of individual user views of portions of the database, also referred to as a subschema.The internal-level schema provides a low-level view of the database.23©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartSchemasrrJackson 210Houston 100xxxxxxxxxxxxxxMapping external level views to conceptual level schemaSubschema ASubschema BSubschema CInventorySalesCustomerCash receipt24©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartSchemasMapping conceptual level facts to internal level descriptionsInventorySalesCustomerCash receiptInventory Record Item number – integer (5), non-null, index = itemx Description – character (15)25©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartThe Data DictionaryThe data dictionary contains information about the structure of the database.For each data element stored in the database, such as the customer number, there is a corresponding record in the data dictionary describing it.26©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartThe Data DictionaryThe data dictionary is often one of the first applications of a newly implemented database system.What are some inputs to the data dictionary?records of any new or deleted data elementschanges in names, descriptions, or uses of existing data elements27©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartThe Data DictionaryWhat are some outputs of the data dictionary?reports useful to programmers, database designers, and users of the information systemWhat are some sample reports?lists of programs in which a data item is usedlists of all synonyms for the data elements in a particular file28©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDBMS LanguagesEvery DBMS must provide a means of performing the three basic functions:Creating the databaseChanging the databaseQuerying the databaseThe sets of commands used to perform these functions are referred to as the data definition, data manipulation, and data query languages.29©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDDL LanguageThe data definition language (DDL) is used to...build the data dictionary.initialize or create the database.describe the logical views for each individual user or programmer.specify any limitations or constraints on security imposed on database record or fields.30©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDML LanguageThe data manipulation language (DML) is used for data maintenance.What does it include?updating portions of the databaseinserting portions of the databasedeleting portions of the database31©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDQL LanguageThe data query language (DQL) is used to interrogate the database.The DQL retrieves, sorts, orders, and presents subsets of the database in response to user queries.32©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartLearning Objective 4Create a set of well-structured tables to properly store data in a relational database.33©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartBasic Requirements of the Relational Data ModelEach column in a row must be single valued.Primary keys cannot be null.Foreign keys, if not null, must have values that correspond to the value of a primary key in an other relation.All non-key attributes in a table should describe a characteristic about the object identified by the primary key.34©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartAnomalies That May Occur in Non-Normalized Relational TablesUpdate Anomaly: When changes (updates) to data values are not correctly recorded.Instead of having to update once, each record in the single table has to be updated individually in order to avoid inconsistencies in the database.35©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartAnomalies That May Occur in Non-Normalized Relational TablesInsert Anomaly: There is no way to store information about one entity in the database without it being associated with another entityIn the text, we would not be able to store information on new customers without their being associated with transactions first!36©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartAnomalies That May Occur in Non-Normalized Relational TablesDelete Anomaly: Unintended results arising from deleting a row of data pertaining to one entity and resulting in the deletion of data regarding another entity as well.In the text, if a particular Inventory item were discontinued and hence removed from the database table, we would lose information on the customer associated with that inventory item as well.37©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartApproaches to Database DesignNormalizationStarts with the assumption that all data is initially stored in a large non-normalized table.This table is then decomposed using a set of normalization rules to create a set of tables in the Third Normal Form.Semantic Data ModelingThe database designer uses his/her knowledge about the business structure to create a set of relational tables.38©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartDatabase Systems and theFuture of AccountingDatabase systems have the potential to significantly alter the nature of external reporting.Perhaps the most significant effect of database systems will be in the way that accounting information is used in decision making.39©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/SteinbartEnd of Chapter 440©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart