DATA FILES |
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| by Ted Peterson |
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| If you are new to computers you may not know what it means when someone starts talking about data files. You use many files every day without knowing about it. The best example is the phone book. All the parts are there - a collection of fields of data (first name, last name, phone number and address. ) which is a record of each person that has a phone number and is in the phone book that can be called the file. If you have 2 phone books, one will be alphabetical by user called the white pages and the other by categories called the yellow pages. |
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| Data files cannot contain all the data in memory and have a reasonable amount of records, or if they do, the files will be way too big to work with. What we do is maintain indexes of data that resides on the hard drive. It is first located and then reassembled for use by the program to display |
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| There are two types of data files, relational and flat files. In a flat file format all information to be stored , retrieved and manipulated must be on each record and on the same file. Fields that may contain data in only a few cases are on each record occupy blank space in memory and slow processing by the computer. You cannot compare or combine data from different data files even if they have some information in common unless you manually print the information out and enter it again. In addition you may be limited by the number of fields allowed on each record. In a relational data file you can combine, extract, compare and what have you from different sets of data. This can allow you to have many fields if you establish a link between them. Record sizes can be smaller if data is organized such that each data file records contain fields that would be filled on most records. If you did this you could then have another file with the items that are only on a few records and have a link that would go to that extra information. |
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| Keeping some things separate enables your computer to work faster and more efficient. |
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| If you are setting up a data file you will have to do some or all the following: |
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| a. Decide what data is needed and break then into different fields |
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| b. Estimate the length in characters or numbers of each field so that it will have room. You may not be able to make it bigger. |
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| c. Make sure you have the correct number of fields as you may not be able to add to the total. |
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| d, If a large number of records will not use a field set up a relational data field and use a loop to retreive the extra information. |
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| e. Enter the field in order that would be best for you. |
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| f. When you sort, sort on the field most likely to be used the most. |
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