Carrying Links Across Files

 Carrying Links Across Files.

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If you have more than two files, some links may need to be carried across files. Here is a set of files showing the survey shots:

 

COW.DAT      A1->A2    A2->A3    A3->A4    A4->A5

TREE.DAT     A3->B1    B1->B2    B2->B3    B3->B4

DOG.DAT      A4->C1    C1->C2    C2->C3    C3->C4

 

In this situation, there is a connection between the first file and the two remaining files. The important thing to note is that one station has to be "carried" from the first file to the third. This is because the Compiler "forgets" stations between files. In the example above, station A4 in the first file, is the link to the third file. Since the compiler forgets all stations after processing COW.DAT and TREE.DAT, you must to tell the compiler not to forget A4 after processing both COW.DAT and TREE.DAT. In other words, we need to "carry" A4 from COW.DAT, through TREE.DAT to DOG.DAT. Here are the links for these files:

 

COW.DAT        -- No Links

TREE.DAT        -- A3, A4

DOG.DAT        -- A4

 

As you can see, A4 is linked into TREE.DAT, but it is not used by TREE.DAT. It is simply carried forward so it can be used in DOG.DAT.