Advanced Accounting Information Systems Day 10 answers Organizing and Manipulating Data September 16, 2009

Announcements –Return Quiz 3 –Business Week – Free food at noon today –Assignment 2 is posted –Graduate student papers

Objectives Understand normalization process Understand techniques for validating data inputs Understand the importance of extracting data from database and AIS uses of such extractions Create simple and multitable queries using Access Understand object-oriented and multimedia databases Be familiar with data warehouses and their uses in accounting applications

Questions for today What are the two methods to design databases? What are the advantages / disadvantages of each? If you wanted to use a bottom/up approach to designing a database, which method would you use? If you wanted to use a top/down approach to designing a database, which method would you use?

Questions for today Review first normal form –Definition –Examples of concerns Data redundancy Insertion anomaly Deletion anomaly Second normal form –Definition –Examples of concerns Transitive relationship Third normal form

Question for today What is a database management system? –Process of examining and arranging file data in a way that helps avoid problems when organizations use or modify them later –Alternative to data modeling concepts such as ERD, organizations may use normalization to organize the data intelligently

Question for today Describe the three problems associated with a database in first normal form –Data redundancy –Insertion anomaly –Deletion anomaly

Question for today What is a data warehouse?

What is wrong with flat files? Flat files – files with no sequence or order to them – student grades of an examination in random order –Almost impossible to find a particular record easily (because records are not stored systematically), link files to one another to provide information from related records store file data efficiently

Three levels of normalization we will look at First normal form Second normal form Third normal form

First normal form (INF) All record’s attributes (data fields) are well defined and information can be stored as a flat file – compare Figure 14.1 to 14.2 Problems remain –Data redundancy –Insertion anomaly –Deletion anomaly

Second normal form (2NF) Database is in first normal form and all the data items in each record depend on the record’s primary key Problem remain –Field A determines value in field B

Third normal form (3NF) Database is in second normal form and contains no transitive dependencies (i.e. no relationships where data field A determines data field B) Actions available with 3NF –Avoids insertion anomaly –Avoids deletion anomaly

DBMS Software system that allows users to create database records, delete records, access specific information, select (query) records for viewing or analysis, alter database information, reorganize records as needed Not a database Examples – Access, dBASE, paradox, FoxPro, DB2, Oracle, Sybase, SQL Server

Data Validation DDL of DBMS –Enables users to define the record structure of any particular database table –Validation techniques Proper data types for fields Input masks – telephone numbers, ssn, date Default values – 40 hours per week Validation rules – between 1 to 100 Referential integrity – Cascade update – Cascade downward

Extracting Data from Databases: Data Manipulation Languages Schema –Map or plan of the entire database Subschema –Subset of information in database – designed to meet user needs Queries –Allow database developers to create customized subschemas Dynaset –Dynamic subset of a database that you create with such queries

Creating Action Queries Update queries –Allows user to alter selected table records systematically Append queries –Allow user to append records from one table to the end of another table Delete queries –Allow user to delete table records selectively Make-table queries –Allow user to create a new table from the records that you select in an existing table

Creating Action Queries Find-duplicate queries –Allows user to find records with duplicate entries in specified fields Find-unmatched queries –Allow user to find the records in one table with no matching records in another table Crosstab queries –Allow user to perform statistical analysis of the data ina table and provides the cross-tabulation results in a row-and – column format similar to a pivot table in a spreadsheet

Guidelines for Creating Queries Spell accurately – look out for Case sensitivity Specify AND and OR correctly Be sure to JOIN tables properly Name queries systematically Choose data fields selectively

Structured Query Language Select attribute(s) From table(s) Where restrictions and joins Group by Order by

More complex databases Object-oriented Multi-media Multidimensional databases

More complex databases Data warehouses (enterprise wide systems) –Pool data from separate applications into a large, common body of information –Useful if data warehouses include –Advantage –Need to standardize and scrub (clean) data to ensure uniform accuracy and consistency –look at restaurant example – p Data marts –

First SQL Practice Marcia Felix Corporation –Problem –Employee table – Figure 14-15

Questions for Friday Identify and describe five basic features of SQL