The VIA location mode is used to group (cluster) records that are likely to be accessed together on the same page or as close to each other as possible. This location mode is also sometimes referred to as clustering.
At Commonweather, for example, employee expertise is usually retrieved in conjunction with information about an employee. Therefore, EXPERTISE records are stored VIA the EMP-EXPERTISE set so that they will be clustered around their owning EMPLOYEE record.
In the following figure, the EMPLOYEE records are randomly located on four pages using the CALC location mode. The EXPERTISE records are located on the same pages as their respective owners in the EMP-EXPERTISE set through the VIA location mode. This enables both employee and expertise information to be retrieved with a single page access.
It is also possible to store records via a system-owned index. In this situation, the target page for a new record is the page of the prior record within the index. Consequently, the indexed record occurrences tend to be physically placed within the area in the same order as their entries occur within the index. If the index is sorted on a symbolic key, the record occurrences tend to be physically sequenced in the order of their respective index key values.
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