Lesson Notes By Weeks and Term - Senior Secondary School 2

SUBJECT: I.C.T.

CLASS:  SS 2

DATE:

TERM: 2nd TERM

 
WEEK 2

TOPIC: CONCEPT OF COMPUTER FILES

Computer files: Computer files are the most basic unit of data that users can store on a disk. Every program, image, video, song employee numbers, a 3-digit, and document is stored as a file

Record: A record is a collection of related data items or fields. Each record normally corresponds to a specific unit of information. For example, employee number, employee’s name, basic salary and house rent allowance.

Field: Data items are physically arranged as fields in a computer file. Their length may be fixed or variable. Since all individuals have 3 digits field is required to store the particular data. Hence, it is a fixed field. In contrast, since customer’s name varies considerably from one customer to another, a variable amount of space must be available to store this element. This can be called variable field.

Data item: Data item is the smallest unit of information stored in computer file. It is a single element used to represent a fact such as an employee’s name, item price and so on.

TYPES OF DATA ITEMS

Numeric: this type of data item consists of numbers 0-9.

Alphabet: this type of data item consists of letters A-Z.

Alphanumeric: also known as alphameric is a combination of alphabetic and numeric characters, and is used to describe the collection of Latin letters and Arabic digits or a text construct from this collection. There are either 36 (single case) or 62(case-sensitive) alphanumeric characters. The alphanumeric character set consists of the numbers 0-9 and letters A-Z.

File structure:

Data: a data item is the smallest unit of information stored in computer file.

 Field: is a collection of related items.

Record:  is a collection of related fields.

File: the collection of records is called a file

Types of file organization method

Serial:  A serial file is one which the records have been stored in the order in which they have arisen. They have not been sorted into any particular order. An example of a serial file is an unsorted transaction file. A shopping list is an example of a non-computerized serial file. Serial files can be stored on tape, disc or in memory. Sequential: in sequential file organization, records are organized in the sequence by which they were added. A sequential file contains records organized in the order they were entered. The order of the records is fixed. The records are stored and sorted in physical, contiguous blocks within each block the records are in sequence. Records in these files can only be read or written sequentially.

Indexed: An indexed file organization contains reference numbers, like employee numbers, that identify a record in relation to other records. These references are called the primary keys that are unique to a particular record. Alternate keys can also be defined to allow alternate methods of accessing the record. For example, instead of accessing an employee’s record using employee numbers, you can use an alternate key that reference employees by departments. This allows greater flexibility for users to randomly search through thousands of records in a file. However, it employs complex programming in order to be implemented.

Random file: This is the file organized via an index. Also called a “direct file” or “direct access file,’’ it enables quick access to specific records or other elements within the file rather than having to read the file sequentially. The index points to a specific location within the file, and the file is read from the that point.

Methods of accessing files:

Serial files:  To access a serially organized file is serially. 

Sequential files: the method of access used is still serial but of course the files are now in sequence, and for this reason the term sequential is often used in describing serial access of a sequential tape file. It is important to note that to process (e.g. update) a sequential master tape file, the transaction file must also be in the sequence of the master file. Access is achieved by first reading the transaction file and then reading master file until the matching record (using the record keys) is found. Note therefore that if the record required is the twentieth record on the file, in order to get it into storage to process it the computer will first have to read in all nineteen proceeding records.

Random files: Generally speaking the method of accessing random files is RANDOM. The transaction record keys will be put through the same mathematical formula as were the keys of the master records, thus creating the appropriate bucket address. The transactions in random order are then processed against the master file, the bucket address providing the address of the record required.

Computer files classification:

Master file: there are files of a fairly permanent nature, e.g. customer ledger, payroll, inventory, and so on. A feature to know is the regular updating of these files to show a current position. For example, customer’s order will be processed, increasing the “balance owing “figure on a customer ledger record. It is seen therefore that master records will contain both data of a static nature, e.g. a customer name, address, and data that, by its nature will change each time a transaction occurs, e.g. the” balance” figure already mentioned.

Transaction file: This is also known as movement file. This is made up of various transactions created from the source documents. In a sales ledger application the file will contain all the orders received at a particular time. This file will be used to update the master file. As soon as it had been used for this purpose it is no longer required. It will therefore have a very short life, because it will be replace by a file containing the next batch of orders.

Reference files:  A file with a reasonable amount of permanency. Examples of data used for reference purposes are price lists, tables of rates of pay, names and addresses.

Criteria for classifying computer files: Criteria for classifying computer files are:

• By nature of content: it refers to the nature of file content.
• By organization method: it refers to the way files are arranged e.g. . Serial, sequential, random and so on.
• By storage medium: it refers to storage devices in which a file’s’ could only be stored such as magnetic or optical disk and magnetic tape and so on.

Reading Assignment: Reading Assignment: 

Hiit @ School, Computer Studies for Senior Secondary Education. Pgs 89 - 91.

EVALUATION

1. Define the following terms; 

1. Computer files
2. Record
3. Field
4. Data Item

1. Explain the classification of computer file.

WEEKEND ASSIGNMENT

OBJECTIVE

1. One of the following are NOT a computer file classification

1. Reference file    b. Random file     c. Master file        d. Transaction file

1. __________ is a collection of related fields

1. Data    b. Field    c. Record    d. file

1. The smallest unit of information stored in computer file is called ________

1. Files    b. Data item    c. Record    d. Indexed

1. The following are types of file organization method EXCEPT _________

1. Serial    b. Sequential    c. Transaction    d. Indexed

1. A file with reasonable amount of permanency is known as__________ file.

1. Reference files    b. Master file    c. Transaction file    d. serial file

THEORY

1. State the criteria for classifying computer files.

1b   Draw a sample of file structure

1. List and explain the different method of accessing files.

2b   List and explain types of file organization method.