FILES AND FILE STRUCTURE
COMPUTER FILES
A file is a collection of related records that give a complete set of information about a certain item
or entity. A file can be stored manually in a file cabinet or electronically in computer storage
devices. Computerized storage offers a much better way of holding information than the manual
filling systems, which heavily rely on the concept of the file cabinet.
Advantages of computerized filling system: –
i. Information takes up much less space than the manual filing
ii. It is much easier to update or modify information
iii. It offers faster access and retrieval of data
iv. It enhances data integrity and reduces duplication
v. It enhances security of data if proper care is taken to secure it.
Elements of computer file
A computer file is made up of three elements: characters, fields and records.
i. Characters
A character is the smallest element in a computer file and refers to letter, number or symbol that can be entered, stored and output by a computer. A character is made up of seven or eight bits depending on the character coding scheme used.
ii. Field
A field is a single character or collection of characters that represents a single piece of data. For example, the student’s admission number is an example of a field.
iii. Records
A record is a collection of related fields that Represents a single entity, e.g. in a class score sheet, detail of each student in a row such as admission number, name, total marks and position
make up a record.
Description of Computer files
Computer files are classified as either physical or logical
Logical files:
A computer file is referred to as logical file if it is viewed in terms of what data item it contains and details of what processing operations may be performed on the data items.
It does not have implementation specific information like field, data types, size and file type. Logical files do not contain data. They contain a description of records found in one or more physical files. A logical file is a view or representation of one or more physical files. Logical files that contain more than one format are referred to as multi-format logical files. If your program processes a logical file which contains more than one record format, you can use a read by record format to set the format you wish to use.
As opposed to a logical file, a physical file is viewed in terms of how data is stored on a storage media and how the processing operations are made possible. Physical files have implementation specific details such as characters per field and data type for each field. Physical files contain the actual data that is stored on the system, and a description of how data is to be presented to or received from a program. They contain only one record format, and one or more members. Records in database files can be externally or program-described. A physical file can have a keyed sequence access path. This means that data is presented to a program in a sequence based on one or more key fields in the file.
