File Processing and Data Management Concepts

1. Chapter 15 File Processing and DataManagement Concepts A field may be a single character or number, or it may be composed of many characters or numbers. • Logical grouping of fields are called records. • Records are groups of data items that concern a certain entity such as an employee, a customer, a vendor, or an invoice. • A record structure has occurrences, also called instances.

2. Introductory Terminology • In a fixed-length record, both the number of fields and the length of each field are fixed. • Most records stored on direct-access storagedevices (DASDs) are fixed length. • In variable-length records, the width of the field can be adjusted to each data occurrence. • A trailer record is an extension of a master record.

3. Introductory Terminology • The terms segment, group, and node(simpul) are shorthand for repeated groups. • A segment can be written as follows: • PART (PART_NO, PNAME, TYPE, COST) • SUPPLIER (PVEND) • LOCATION (WARHSE, LOC)

4. Introductory Terminology • Segments, unlike simple records, have parents and children. Part Supplier Location

5. Introductory Terminology • A key or record key is a data item or combination of data items that uniquely identifies a particular record in a file. • What is a primary (sort) key? • It is the first field used to sort the records in a file. • What is a secondary (sort) key?

6. Introductory Terminology • 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. • What is relative random order? • The term relative random order applies to a field on which the file is not sorted.

7. The Evolution of Database Technology Period Event Related Database Technique 1960s Mainframe File Systems environments Database Database management systems management On-line information Text management services

8. The Evolution of Database Technology Period Event Related Database Technique 1970s Expert systems Inference and deduction Object-oriented Inheritance and programming abstraction 1980s Hypertext systems Association 1990s Intelligent Combination of database systems techniques

9. Database Management Systems and Their Architecture Database contents Uses of database Desired reports Information to be reviewed Conceptual Level • Logical data structures: • Tree (hierarchical) • Network • Relational Logical Level

10. Database Management Systems and Their Architecture • Access methods: • Sequential • Indexed-sequential • Direct Physical Level • The entity-relationship (E-R) data model is a conceptual model for depicting the relationships between segments in a database.

11. Conceptual Architecture • The term entity is used instead of segment. • The term attribute is used to refer to individual fields or data items. • 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.

12. Logical Data Structures • The relationships that exist between the segments in the database are determined by the logical data structure, also called the schema or database model. • What are the three major models of logical data structure? • Tree or hierarchical structures • Network structures • Relational models

13. Logical Data Structures • 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. • A child node cannot have more than one parent.

14. Logical Data Structures • A network structure is one that allows a child segment to have more than one parent. • A network is a more general data structure than a tree.

15. Logical Data Structures • There are various ways to implement tree and network structures. • 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). • A record may be a part of several lists.

16. Logical Data Structures • A ring structure differs from a list structure in that the last record in the ring list points back to the first record. • What is a multiple-ring structure? • In this type of structure several ring organizations pass through individual records.

17. Logical Data Structures List Structure Location of first record Attribute 2 Red 1 Blue Pointer field to next record End-of-list indicator Index 1 2 4 3 4 5 5 Records

18. Logical Data Structures Ring Structure Location of first record Attribute 2 Va 3 Ky Pointer field to next record Pointer field to first record Index 1 2 4 3 4 5 5 2 Records

19. Logical Data Structures • What is the relational model? • This model is a logical data structure that views the database as a collection of two-dimensional tables. • Information is extracted from tables using relational algebra. • Certain rules called normal forms govern the creation of tables.

20. Logical Data Structures • What are the three normal forms? • In the first normal form tables are divided to eliminate repeated groups. • In the second normal form tables are divided so that no key determines the values of a nonkey field. • In the third normal form tables are divided so that no nonkey field determines the values of another nonkey field.

21. Sequential Accessed Files • In a sequential access file, records can only be accessed in their predefined sequence. • 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. • One important type of indexed file is an indexed-sequential file.

22. Indexed Files • 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. • These files are frequently referred to as ISAM files that consists of three distinct areas: • The index • The prime area • The overflow area

23. Indexed Files • The index is a map that relates the key fields of records to their corresponding addresses in the prime area. • The prime area is the portion of the disk on which the actual records are written. • 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.

24. Economic Relations between Organization Techniques • The basic economics of file processing are largely determined by the activity ratio. • What is the activity ratio? • It is the number of accessed records divided by the number of records in the file. • The second economic consideration concerns response time.

25. Economic Relations between Organization Techniques • What is response time? • It is the length of time the user must wait for the system to complete an operation. • 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.

26. Database Management Systems and Databases in Practice • All DBMSs contain three common attributes for managing and organizing data. • What are these attributes? • Data description language (DDL) • Data manipulation language (DML) • Data query language (DQL)

27. Database Management Systems and Databases in Practice • What is a schema? • It is a synonym for logical data structure of a database. • 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.

28. Database Management Concepts Independent Files Application One X Y A B Application Two X Y C D