 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood A field may be a single character or number, or it may be composed of many characters or numbers. l Logical grouping of fields are called records. l Records are groups of data items that concern a certain entity such as an employee, a customer, a vendor, or an invoice. l A record structure has occurrences, also called instances. File Processing and Data Management Concepts Chapter 15

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Introductory Terminology l In a fixed-length record, both the number of fields and the length of each field are fixed. l Most records stored on direct-access storage devices (DASDs) are fixed length. l In variable-length records, the width of the field can be adjusted to each data occurrence. l A trailer record is an extension of a master record.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Introductory Terminology l The terms segment, group, and node(simpul) are shorthand for repeated groups. l A segment can be written as follows: l PART (PART_NO, PNAME, TYPE, COST) l SUPPLIER (PVEND) l LOCATION (WARHSE, LOC)

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Introductory Terminology l Segments, unlike simple records, have parents and children. Part Supplier Location

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Introductory Terminology l A key or record key is a data item or combination of data items that uniquely identifies a particular record in a file. l What is a primary (sort) key? l It is the first field used to sort the records in a file. l What is a secondary (sort) key?

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Introductory Terminology l It is a field used to determine relative position among a set of records when the primary key has the same value in each record of the set. l What is relative random order? l The term relative random order applies to a field on which the file is not sorted.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood The Evolution of Database Technology PeriodEventRelated Database Technique PeriodEventRelated Database Technique 1960sMainframeFile Systems environmentsDatabase management systemsmanagement On-line informationText management services 1960sMainframeFile Systems environmentsDatabase management systemsmanagement On-line informationText management services

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood The Evolution of Database Technology PeriodEventRelated Database Technique PeriodEventRelated Database Technique 1970sExpert systemsInference and deduction Object-orientedInheritance and programmingabstraction 1970sExpert systemsInference and deduction Object-orientedInheritance and programmingabstraction 1980sHypertext systemsAssociation 1990sIntelligentCombination of database systemstechniques 1990sIntelligentCombination of database systemstechniques

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Database Management Systems and Their Architecture Conceptual Level Conceptual Level Database contents Uses of database Desired reports Information to be reviewed Logical Level Logical Level Logical data structures: Tree (hierarchical) Network Relational

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Database Management Systems and Their Architecture Physical Level Physical Level Access methods: Sequential Indexed-sequential Direct l The entity-relationship (E-R) data model is a conceptual model for depicting the relationships between segments in a database.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Conceptual Architecture l The term entity is used instead of segment. l The term attribute is used to refer to individual fields or data items. l The object-oriented modeling technique (OMT) is a conceptual model for depicting the relationships between segments in a database that views the components of the system being modeled as object classes.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l The relationships that exist between the segments in the database are determined by the logical data structure, also called the schema or database model. l What are the three major models of logical data structure? 1 Tree or hierarchical structures 2 Network structures 3 Relational models

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l In a tree structure each node represents a set of fields (i.e., a segment), and a node is related to another node at the next highest level of the tree. l A child node cannot have more than one parent.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l A network structure is one that allows a child segment to have more than one parent. l A network is a more general data structure than a tree.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l There are various ways to implement tree and network structures. l In a list organization each record contains one or more pointers (fields) indicating the address of the next logical record with the same attribute(s). l A record may be a part of several lists.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l A ring structure differs from a list structure in that the last record in the ring list points back to the first record. l What is a multiple-ring structure? l In this type of structure several ring organizations pass through individual records.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures List Structure Records Index Pointer field to next record End-of-list indicator Location of first record Attribute 2 Red 1 Blue 4 5

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures Ring Structure Records Index Pointer field to next record Location of first record Attribute 2 Va 3 Ky Pointer field to first record

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l What is the relational model? l This model is a logical data structure that views the database as a collection of two- dimensional tables. l Information is extracted from tables using relational algebra. l Certain rules called normal forms govern the creation of tables.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Logical Data Structures l What are the three normal forms? l In the first normal form tables are divided to eliminate repeated groups. l In the second normal form tables are divided so that no key determines the values of a nonkey field. l In the third normal form tables are divided so that no nonkey field determines the values of another nonkey field.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Sequential Accessed Files l In a sequential access file, records can only be accessed in their predefined sequence. l An index file is one where an attribute has been extracted from the records and used to build a new file whose purpose is to provide an index to the original file. l One important type of indexed file is an indexed-sequential file.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Indexed Files l An indexed-sequential file is a sequential file that is stored on a DASD and is both indexed and physically sorted on the same field. l These files are frequently referred to as ISAM files that consists of three distinct areas: 1 The index 2 The prime area 3 The overflow area

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Indexed Files l The index is a map that relates the key fields of records to their corresponding addresses in the prime area. l The prime area is the portion of the disk on which the actual records are written. l The overflow area is a separate section of the disk that is allocated to the file to allow additions to be made without extensive processing.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Economic Relations between Organization Techniques l The basic economics of file processing are largely determined by the activity ratio. l What is the activity ratio? l It is the number of accessed records divided by the number of records in the file. l The second economic consideration concerns response time.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Economic Relations between Organization Techniques l What is response time? l It is the length of time the user must wait for the system to complete an operation. l Database management systems (DBMSs) are computer programs that enable a user to create and update files, to select and retrieve data, and to generate various outputs and reports.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Database Management Systems and Databases in Practice l All DBMSs contain three common attributes for managing and organizing data. l What are these attributes? 1 Data description language (DDL) 2 Data manipulation language (DML) 3 Data query language (DQL)

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Database Management Systems and Databases in Practice l What is a schema? l It is a synonym for logical data structure of a database. l In the absence of integration, each type of accounting application such as sales, payroll, and receivables will maintain separate, independent data files and computer programs.

 2001 Prentice Hall Business Publishing, Accounting Information Systems, 8/E, Bodnar/Hopwood Database Management Concepts Independent Files Application One Application Two XYBA XYCD