Concept of computer files

A file is a collection of data that is treated as a single unit on a peripheral device.

1. CONCEPT OF COMPUTER FILES I Tuesday, October 18, 2016

2. LEARNING OUTCOMES At the end of the lesson, I should be able to: Define the following: File Record Field List three types of data Draw the order in a file structure

3. Definition of computer files Computer files are a collection of related records. They are the most basic unit of data that users can store on a disk. Every program, image, video, song and document is stored as a file.

4. Definition of Record A record is a collection of related data items or fields. Each record normally corresponds to a specific unit of information. Examples are: Employee’s name, basic salary and house rent allowance.

5. Field A field is a collection of related data items. It a space allocated for a particular item of information. A tax form for example contains a number of fields; one for your name, one for your tax identification number (TIN), one for your income and so on.

6. Data Item Data item is the smallest unit of information stored in a computer file. It is a single element used to represent a fact such as an employee’s name, item price. Data items are physically arranged as fields in a computer file.

7. Types of Data items Numeric data consist of numbers from 0 – 9 Alphabetic data consist of letters A –Z Alphanumeric data is a combination of numbers and letters, can also refer to collection of Latin letters and Arabic digits or text constructed from these collection. There are either 36 (Single case) or 62 (Case Sensitive) alphanumeric characters. The alphanumeric data set consist of number 0-9 and letters A – Z.

8. File Structure Summary of data items: The data is the smallest unit of information stored in a computer file A field is a collection of related data items A record is a collection of related fields The collection of record is a file The structure of a file in systematic order from top to bottom

9. Evaluation Define the following: File Record Field List three types of data List the order in a file structure

10. CONCEPT OF COMPUTER FILES II Tuesday, October 18, 2016

11. LEARNING OUTCOMES At the end of the lesson, I should be able to: -identify types of file organization -outline methods of accessing files -Classify computer files -itemize criteria for classifying computer files

12. File organization refers primarily to the logical arrangement of data in a file system.

13. Choosing a file organization is a design decision, hence it must be done having in mind the achievement of good performance with respect to the most likely usage of the file. The criteria usually considered important are:    1. Fast access to single record or collection of related records.    2. Easy record adding/update/removal, without disrupting .    3. Storage efficiency.    4. Redundancy as a warranty against data corruption.

14. TYPES OF FILE ORGANIZATION Serial Sequential Indexed Sequential Direct Access /Random Access

15. Serial File Organization A collection of records No particular sequence Cannot be used as master Used as temporary transaction file Records stored in the order received can be stored on magnetic tape e.g. VHS

16. Sequential File Organization A collection of records Stored in key sequence Adding/deleting record requires making new file Used as master files Can be stored on optical disk, memory stick and magnetic disk.

17. Sequential file

18. Advantages Simple file design Very efficient when most of the records must be processed e.g. Payroll Very efficient if the data has a natural order Can be stored on inexpensive devices like magnetic tape.

19. Disadvantages Entire file must be processed even if a single record is to be searched. Transactions have to be sorted before processing Overall processing is slow

20. Direct (Random) File Organization Records are read directly from or written on to the file. The records are stored at known address. Address is calculated by applying a mathematical function to the key field.

21. Direct (Random) File Organization A random file would have to be stored on a direct access backing storage medium e.g. magnetic disc, CD, DVD Example : Any information retrieval system. Eg Train timetable system.

22. Advantages Any record can be directly accessed. Speed of record processing is very fast. Up-to-date file because of online updating. Concurrent processing is possible.

23. Disadvantages More complex than sequential Does not fully use memory locations More security and backup problems

24. Indexed sequential file Each record of a file has a key field which uniquely identifies that record. An index consists of keys and addresses . An indexed sequential file is a sequential file (i.e. sorted into order of a key field) which has an index . A full index to a file is one in which there is an entry for every record.

25. Indexed-sequential organization

26. Indexed sequential file

27. Advantages Provides flexibility for users who need both type of accesses with the same file Faster than sequential An indexed sequential file can only be stored on a random access device only e.g. magnetic disc, optical disk (CD, DVD etc.)

28. Disadvantages Extra storage space for the index is required

29. Methods of accessing computer files Serial file access Sequential file access Direct/Random file access

30. Computer file classification Mater file Transaction file Reference/work file

31. Computer file classification A file is a collection of data that is treated as a single unit on a peripheral device. TYPES OF FILES- Master file It contains record of permanent data types. They are created when you install your business.

32. Transaction file Contains data which is used to update the records of master file. Ex-address of a customer. Transaction files also serves as audit trails and history of the organization. Reference/Work files This is a file with reasonable amount of permanency. Examples of data used for reference purposes are price list, tables of rates of pay, names and addresses.

33. Criteria for Computer file classification Criteria for classifying computer files are: By nature of content: refers to the nature of file content By organization method: refers to the way files are arranged e.g. serial, sequential, random etc. By storage medium: refers to storage devices in which a file could only be stored such as magnetic or optical disk and magnetic tape.

34. Evaluation -identify types of file organization -outline methods of accessing files -Classify computer files -itemize criteria for classifying computer files

35. Assignment 1. Read up the topic: “handling computer files”. 2. Outline the operating procedure for computer data processing [see pages 86 & 87 of your ICT textbook]

36. Terminologies Serial Sequential Random Index