7.1
Files - basics for HL

All of the data about Jerry James is a record .

Tutor is a field.

Boarder is a boolean type .

File terminology

A file may be defined as "an organised collection of related records ". A record contains organised data about a single object and the data is contained in fields each of which is of a defined type .

Quite often, each record is given a unique identifier; in the above example two students could have the same name, the key field (ID) would distinguish their records.

If this wasn't done a mix up could occur and, for example, the wrong parents could get the wrong reports.

One or more fields could be used to keep records in a certain order (eg alphabetical) in which case the file is said to be ordered.

Recall, access methods
The two main ways of storing data on backing store are sequential-access and direct-access.

For example, a payroll program has to access the data file containing all the data on all of a company's employees, it accesses this data one record at a time, one after the other, this is sequential access.

Direct access (sometimes called random access) would be used, for example, in a supermarket where details of all of the items for sale are held in a file, the computer needs to locate an item quickly by moving directly to its record.

Direct access requires some kind of index to be held on the medium (the material storing the data).

Thus records can be ordered or unordered and accessed sequentially (one at a time), the required record will be identified by the key field.

related: [ Topic 7 home | next: partially-indexed files ]

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