TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

502 Chapter11
B-Tree Indices
Overview of B-Tree Indices
have keys that satisfy the DBFIND criteria. The total of all
corresponding chains in a detail data set is referred to as a
super-chain. TurboIMAGE/XL fetches each qualifying
master entry in order to determine the total number of
associated detail entries to calculate the sum of the chain
counts. To retrieve all qualified entries in a detail data set
using DBGET, TurboIMAGE "walks" (traverses) this
super-chain.
B-Tree Search is the same as B-Tree DBFIND.
Super-chain is the sum of all detail data set chains involved in the
B-Tree DBFIND.
Trailing-@ Search is a B-Tree search where only the characters left of the @
(wildcard character) of the argument are compared to
qualify an entry. (For example, "cat@" is a trailing-@
search, but "cat@dog" is not and the result will be the
same for both arguments. That is, "dog" will be ignored.)
Wildcard Character refers to a printable ASCII character. The default is @
which means "matches all trailing characters" (unlike "?"
or "#" in MPE terms).
BTREEMODE1 is an option which can be turned ON or OFF using the SET
command of DBUTIL or programmatically using
DBCONTROL. When it is ON, DBFIND mode 1 of an item of X
or U type having a B-Tree index (explicit or implicit), and
having a wildcard character in the argument will result in
a B-Tree search. The ON option allows applications to
benefit from B-Tree indices without modifying
applications. When it is OFF, which is also the default,
DBFIND mode 1 described above works as it did in releases
prior to a release with the B-Tree index feature (C.07.00).
Simple Argument is a DBFIND argument that consists of a sequence of bytes,
as in DBFIND mode 1 argument in releases prior to a
release with the B-Tree index feature (C.07.00). This is
used predominantly for modes 1, 10, and 21. For DBFIND
modes 1 and 21, an X or U type item having B-Tree index
(explicit or implicit) and having the BTREEMODE1 option
ON, the text is scanned for a wildcard character, if any. If a
wildcard is found, DBFIND is treated as a B-Tree DBFIND.
Otherwise, it is treated as DBFIND in releases prior to a
release with the B-Tree index feature (C.07.00).
Structured Argument is a DBFIND fixed format argument construct introduced
with B-Trees enhancement. It is defined as a record
structure, containing search control information as well as
key data. This is used for DBFIND modes 4 and 24, and is
described later in this chapter.