©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-1 Relational Databases

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-2 Learning Objective 1 Explain the difference between database and file-based legacy systems.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-3 Types of Files Two basic types of files are used to store data. 1 The master file, which is conceptually similar to a ledger in a manual system. 2 The transaction file, which is conceptually similar to a journal in a manual system.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-4 File Approach For many years, companies created new files and programs each time an information need arose. This proliferation of master files created problems: 1 Often the same data was stored in two or more separate files. 2 The specific data values stored in the different files were not always consistent.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-5 File-Oriented Approach Shipping Program Sales Program File 1 Fact A Fact B Fact C File 2 Fact B Fact D Fact E Billing Program File 3 Fact A Fact G Fact E

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-6 Databases The 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-7 Databases Database 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-8 Database Approach Billing Program Shipping Program Database management system Sales Program Fact A Fact B Fact C Fact D Fact E Database

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-9 Learning Objective 2 Describe what a relational database is and how it organizes data.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-10 Relational Databases A 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-11 Relational Databases Each row in a relation, called a tuple, contains data about a specific occurrence of the type of entity represented by that table.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-12 Learning Objective 3 Explain the difference between logical and physical views of a database.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-13 Logical and Physical Views of Data A 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-14 Logical and Physical Views of Data What 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-15 Logical and Physical Views of Data Logical View User ALogical View User B Past Due Accounts Name Balance Days Jackson Houston October Sales by Region Operating system DBMS Database

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-16 Logical and Physical Views of Data Program-data independence is the separation of the logical and physical views of data.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-17 Schemas A schema describes the logical structure of a database. There are three levels of schemas: 1 Conceptual-level schema 2 External-level schema 3 Internal-level schema

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-18 Schemas The 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-19 Schemas rr Jackson 210 Houston 100 xxxxxxx Mapping external level views to conceptual level schema Subschema ASubschema BSubschema C InventorySalesCustomer Cash receipt

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-20 Schemas Mapping conceptual level facts to internal level descriptions InventorySalesCustomer Cash receipt Inventory Record Item number – integer (5), non-null, index = itemx Description – character (15)

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-21 The Data Dictionary The 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-22 The Data Dictionary The 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 elements – changes in names, descriptions, or uses of existing data elements

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-23 The Data Dictionary What are some outputs of the data dictionary? – reports useful to programmers, database designers, and users of the information system What are some sample reports? – lists of programs in which a data item is used – lists of all synonyms for the data elements in a particular file

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-24 DBMS Languages Every DBMS must provide a means of performing the three basic functions: 1 Creating the database 2 Changing the database 3 Querying the database The sets of commands used to perform these functions are referred to as the data definition, data manipulation, and data query languages.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-25 DDL Language The 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-26 DML Language The data manipulation language (DML) is used for data maintenance. What does it include? – updating portions of the database – inserting portions of the database – deleting portions of the database

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-27 DQL Language The 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-28 Learning Objective 4 Create a set of well-structured tables to properly store data in a relational database.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-29 Basic Requirements of the Relational Data Model 1. Each column in a row must be single valued. 2. Primary keys cannot be null. 3. Foreign keys, if not null, must have values that correspond to the value of a primary key in an other relation. 4. All non-key attributes in a table should describe a characteristic about the object identified by the primary key.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-30 Anomalies That May Occur in Non-Normalized Relational Tables Update 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-31 Anomalies That May Occur in Non-Normalized Relational Tables Insert Anomaly: There is no way to store information about one entity in the database without it being associated with another entity In the text, we would not be able to store information on new customers without their being associated with transactions first!

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-32 Anomalies That May Occur in Non-Normalized Relational Tables Delete 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.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-33 Approaches to Database Design Normalization Starts 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 Modeling The database designer uses his/her knowledge about the business structure to create a set of relational tables.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart 4-34 Database Systems and the Future of Accounting Database 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.