When using a query tool such as LANSA/Client, access routes are very important because users do not need to understand the file structure. They only need to nominate a "base" or "starting" file and LANSA can then follow the access route chains to present the other accessible files as simple alternatives.
The relationship between records in any 2 files in any access route is predefined as "1 : 1" or "1 : many". This enables the required screen formats to be automatically designed for the type of information expected.
For example, an access path avoids the question "Given that I have a record from file A, how do I access the associated records in file B"?
File A is always the file definition that is currently being worked upon. File B can be any other physical or logical file known to LANSA.
File A can have many access routes. They could all be from file A to file B, or some could be to any other file that is related to file A.
In addition, access routes can be assigned in a chain. Thus if there is an access route from file A to file B, and an access route from file B to file C, then it is possible to start with a record from file A and locate the associated record(s) in file C.
When you load externally defined files into LANSA or create new LANSA files, you must manually create access routes if you wish to effectively use LANSA/Client or any other query facility over these files.