RevMedia

When moving files around the system, I'm sure that you could not help but notice that a FILECOPY removes all indexes on the destination file. There is some logic in this, but it can make life really difficult when trying to install new versions of software - how can we reinstall the missing indexes?

I know that when I first had this problem I just developed CAPTURE scripts to call up the main menu, go to Files, Indexing, Update etc. etc. This was a mess. More often than not, a "Stickum" on the menu would get in the way and my system would sit there flashing at me as the wrong characters got fed into the wrong screen. I thought that there had to be a better way and started playing around. What I thought must be an easy process turned out to be more complex, but it all revolves around a system subroutine called MAKE.INDEX. (A routine that puts all the extra necessary pointers and records onto the system to tell it that it has an index on a field (or to remove it)).

The calling syntax is for MAKE.INDEX is

CALL MAKE.INDEX(File,Field.name,Old.record,New.record)

where

         File          name of the file the index is on
         Field.name    dict item in the file
         Old.record    compiled dict item before the index was added
         New.record    compiled dict item after the index was added

As you will be aware from the documentation on the utility diskette, indexing information is stored in various fields on the indexed dictionary item. When the dictionary item is filed away, DICT.MFS recompiles it and adds the new object code back into the item before writing it away.

BTREE INDEXES

A BTREE index is one of the most easy to set up. A dictionary item with a BTREE index is distinguished by the presence of a 1 in field 6. Thus to add a BTREE index to a field we would read in the dictionary item for the field, add a 1 into field 6, write the item out again to recompile it, then read it in to a new variable and call MAKE.INDEX. E.g. (assuming no errors encountered)

XREF INDEXES

This is, of necessity, the most complicated index to set up. When you set up an XREF index, a new symbolic field is added into the dictionary which is used to do the XREFing. This field has the name field.name.XREF and contains a call to the system routine XREF with the necessary stop list and delimiter information. Thus to add an XREF index to a field we must first create this extra dictionary item AS WELL AS altering the original dictionary item to tell it that an XREF index exists, by adding the name of the symbolic xref item into field 22 of the original dictionary item. Thus (assuming setup as above)

RELATIONAL INDEXES

This is nearly as simple as BTREEs, it merely requires that the dict item be told what it is related to by putting file*field*sort.order into field 23. Thus using the above example to relate the surname field to NAMES file in the KEYS field in ascending numerical order, (assuming setup as above)