A Join is a temporary connection between two or more data source files that share at least one common field. For example, since the EMPLOYEE data source includes a job code field and the JOBFILE data source also includes a job code field, you can join the two data sources.
The field format and the type must be the same for the common fields, but the field name need not be the same.
After you join two files, each time a record is retrieved from the first file (host file), it also retrieves the matching records from the second file (cross-referenced file).
The following diagram illustrates how Developer Studio can associate each employee in the EMPLOYEE data source with a job description in the JOBFILE data source.
The data source on the left is the host file. The data source on the right is the cross-referenced file.