A data file is a computer file which stores data to be used by a computer application or system, including input and output data. A data file usually does not contain instructions or code to be executed (that is, a computer program). Most of the computer programs work with data files.
A text file (also called ASCII files) stores information in ASCII characters. A text file contains human-readable characters. A user can read the contents of a text file or edit it using a text editor. In text files, each line of text is terminated, (delimited) with a special character known as EOL (End of Line) character. In text files some internal translations take place when this EOL character is read or written.
Examples of text files
A text document (often .txt)
A binary file is a file that contains information in the same format in which the information is held in memory i.e. in the binary form. In binary file, there is no delimiter for a line. Also no translations occur in binary files. As a result, binary files are faster and easier for a program to read and write than the text files. As long as the file doesn’t need to be read or need to be ported to a different type of system, binary files are the best way to store program information.
Examples of binary files
A JPEG image (.jpg or .jpeg)
Data file categories
Closed data file formats, frequently referred to as proprietary format files, have their metadata data elements hidden, obscured or unavailable to users of the file. Application developers do this to discourage users from tampering with or corrupting the data files or importing the data into a competitor’s application.
Open data format files have their internal structures available to users of the file through a process of metadata publishing. Metadata publishing implies that the structure and semantics of all the possible data elements within a file are available to users.
Examples of open data files include CSV, XLS and XML formats such as HTML for storing web pages or SVG for storing scalable graphics.
Any other file which is required to enable the processing of business data to be carried out is a work file (excluding files required for security or audit purposes).
The designer may or may not have to design such files himself.
Examples where he would not be involved in the design would be:
- Work files used by system software or utilities such as sort/merge processers.
- Work files used as intermediate or inter-process files in computer programs at a low level. The design of these files would be better left to the programming team.
If a file is needed to store Data created by one business process before being used by another business process, then the designer would have to be involved. These files are sometimes referred to as transfer files. The temporary files which hold information for printing also fall into this category. Here the designer needs to specify the record definitions required to produce the correctly formatted to output.
Master files are files of a fairly permanent nature, e.g., customer ledger, purchase ledger, inventory pay roll etc. They include some information which is continuously updated by recent transactions. For example, a sales ledger might contain the customer’s names and addresses as well as their current position which is updated periodically.
The description information in a master file may include such items as product code, description, specifications etc. The normal means of updating a master file is by adding, deleting or amending records in the file.
Master files can be further subdivided into two types of files:
- Static master file/Reference files
- Dynamic master files/table files
- Static master files (or reference files):
The business entities that these files describe are at a permanent or semi-permanent nature (e.g., products, suppliers, customers, employees etc.). These are subject to occasional relation.
(ii) Dynamic master files (or table files):
The business entities these files describes are of transitory importance to the business (e.g., customer orders, work orders, job tickets, projects, price lists, wage rates) etc.
Data File Type # 3. Audit File:
Audit files are a particular the of transaction file. They play the same role in computerised information systems as the postings in a traditional manual ledger. They enable the auditor to check the correct functioning of the computer procedures, by storing copies of all the transactions which cause the permanent system file to be altered.
For example, in a sales ledger system, the transactions to be recorded might be:
- Invoice number, data, cash amount for each invoice raised.
- Date and amount of cash received.
- Credit note number, date amount of money credit.
- Account adjustment, amount of money, cross reference to authorisation, adjustment code.
These files will normally be serial, the records being created at the time of the master file update and accumulated in the sequence of the update, on the audit file.
Transaction files are files in which the data relating to business events is recorded, prior to a further stage of processing and are created from source documents used for recording events or transactions. This further processing may be the use of the transaction data to update master files, or the achieving of the transaction for audit purposes.
After the transaction file is processed, it is usually reinitialised, and further transactions are then recorded in it.
Examples of transaction files are:
- Customer’s orders for products (to update an order file)
- Details of price changes for products (to update a product file)
- Details of cash postings in customer accounts (to be held for audit purposes)
- Purchase orders, job cards, invoice dispatch notes etc.
Back Up or Security File:
These files are taken in order to provide back copies, in case of loss or damage to current versions, and arc copies of currently used master files kept in the computer library as a measure of security.
In practice, the designer is unlikely to be involved in the detail design of such files, as he would rely either on system security software (e.g., dump/restore utilities; the transaction logging and recovery routines in teleprocessing monitors); or in batch up date system, in holding superseded versions of master files with back copies of transaction files.
History files are often stored on magnetic tape and are kept in case past information is ever required. For example, an employee who was dismissed three years back may wish to apply for unemployment insurance. The past employee’s record must be retrieved by personnel to complete the necessary paper work.