Predecessor to the Database: Traditional File Processing Records are stored in files. Programs are customized to process the data

File Structure Bit  1 0r 0 Byte  8 bits (number, character, letter, symbol) Field  Grouping of characters into a word or number Record  A group of related fields File  A group of records of the same type Database  A group of related files

File Environments Record / Entity  A collection of fields that contain information concerning a specific thing or event field / attribute  a piece of information that further describes the record key field (primary key) = unique identifier  attribute(s) that uniquely identifies an entity  Example = social security number, course number

How are the records stored and accessed?

Accessing records Stored on secondary storage devices Storage methods  sequential file storage / access records retrieved in the same physical sequence in which they are stored Normally uses magnetic tape Think of your cassette tapes  direct file storage / access access records in any sequence Must know the key of the record Stored on magnetic / optical disks

Direct Access Methods Direct File Access Method  key of the record is mathematically transformed into the actual address of the record (hashing)  Go directly to the address to retrieve the record ISAM  indexed sequential access method  records are stored sequentially on DASD  retrieved through the use of indexes that store the cylinder / track of the record  cylinder / track is then searched sequentially for the record you want

Effect of Data Organization on Processing speed of storage  How long does it take to store the records speed of retrieval  How long does it take to retrieve the records speed of processing  Processing time is suspended while the CPU waits for the record to be retrieved

Traditional File Processing Uses transaction processing A transaction is the record of an event. Requires a Master File, and many transactions files Master File – “permanent” information Transaction file – contains information relevant to the most recent transactions.

Transaction Processing Master File Transaction File

Traditional Files

Limitations of File Processing Separated and Isolated Data Data Duplication (i.e. data integrity) and Confusion Application Program Dependency Incompatible Files Difficult to Represent Users’ Perspectives of Data Lack of Data Sharing and Availability

Advantages of Database Processing Integrated Data Less Duplication of Data Program/Data Independence Easier Representation of Users’ View of Data Restrict Unauthorized Access Backup and Recovery