RISC DISC 1/RISC_DISC_1.iso/pd_share/apps/powerbase/Docs/Utilities

Text File | 1994-10-01 | 10.0 KB | 185 lines

                        Powerbase Utilities
                        ===================

Under this heading we will group a number of things which can be done from
the ‘Utilities’ sub-menu of the icon-bar menu to examine and alter the
structure of an existing database. Note that, if passwords have been set,
you need to open the database with the ‘Manager’-level password to obtain
access to this sub-menu.

Changing the Primary Key
========================
The primary key of a database is determined when it is created, but it is
not fixed for all time. The option provided from the ‘Utilities’ submenu
displays the same dialogue box as is used for creating the primary key in
the first place, but with the addition of two radio buttons, whose function
is described below. The present key structure is shown. Simply alter it to
what you require and click on ‘OK’ or type RETURN. Confirmation is
requested.

Normally the first of the two radio buttons is selected, causing the records
to appear in the same subfiles as they did before. In this case, any
additional indices will still be valid.

If you deselect this radio button with ADJUST (i.e. have neither button
selected) then all the records will be placed in the currently selected
subfile.

Selecting the second radio button also places the records in the current
subfile, but has the additional effect of recovering any “deleted” records,
i.e. records which are still lurking in the ‘Database’ file but aren’t in
the primary key index. In fact this mode of operation ignores the existing
primary key altogether. There is one very important circumstance under which
you would need to do this: when the primary key index is lost or corrupted.

NOTE: You might have a ‘Database’ file but no ‘PrimaryKey’ file at all. This
could happen if you have, for example, created a suitable text file and then
set its type to ‘Database’.  To build a primary key for such a file the only
valid setting for the radio buttons is the one just described, i.e. second
button selected.  To enforce this mode both radio buttons are shaded.

Adjusting the record format
===========================
Minor changes to the screen layout can be made without having to rebuild the
database. Choose the ‘Adjust format’ menu option and you will be presented
with the blank record screen. Clicking MENU over this  brings up the same
menu as you used to create the screen originally, but the field-definition
dialogue box has some options shaded. Thus, you can’t delete fields, add new
ones or alter the data lengths, but you can re-position fields, change
descriptors and tags, and alter the visible lengths. When you have finished
the changes, click on the last option on the menu -  ‘Quit design’.

Another situation in which your control over the screen design will be
limited as above occurs when you have a ‘Form’ file and a ‘Database’ file
but no ‘PrimaryKey’ file. Since this is not yet a functioning database you
will be placed in “restricted design” mode. The ‘Quit design’ option isn’t
used to end the adjustments in this case. Use ‘Save form file’ instead.

Changing the record format
==========================
This is a more drastic change to make, but one can’t foresee all future
needs and you may have to introduce a new field into the record or lengthen
an existing one. This involves rebuilding the whole database. You will need
to create a new application shell with the new ‘Form’ file inside it. The
best way to do this is probably to open the new database directory, copy the
old ‘Form’ file into it, then open the new “database”. Since no ‘PrimaryKey’
or ‘Database’ file yet exists you will be able to modify the screen design
as you wish. You should not, however, go on to complete the empty database
(i.e. don’t choose ‘Default database’ or click on the ‘OK’ button in the
primary key dialogue box) - simply save the ‘Form’ file using the menu
choice provided.

With your old database open, choose the ‘Change format’ option from the
icon-bar menu and drag the new database to the large arrow icon in the
displayed  window. The database will then be rebuilt. Make sure you have
plenty of disc space available before doing this since the original database
remains intact so you need room for it and the new one.

Data from a field in the old database is copied to a field in the new one
which has the same tag. The new Form file must therefore retain the same
tags as the old for data which is to be common to both. If a tag exists in
the old Form file but not in the new Powerbase will assume that the relevant
field has been deleted and data present in that field in the old database
will not be transferred. A tag which is present in the new database but not
in the old is assumed to be a newly-introduced field and will therefore be
left blank.

Merging a second database
=========================
Two databases may be merged provided they have the same record structure.
Selecting ‘Merge database’ displays a window like that used for changing the
record format and you simply drag the second database to the arrow icon.
Powerbase will check that the two record formats are identical and report an
error if they aren’t. If the open database has insufficient free space to
hold the merged records it is automatically extended.

Two radio buttons are also present, as in the dialogue box for rebuilding
the primary key, and their functions are essentially the same. Thus, having
the first selected will merge records into the same subfiles as those they
occupied in the source database. Having neither selected will merge records
into the current subfile of the open database, regardless of where they are
in the source database. Having the second button selected does the same
thing, but also imports records which were “deleted” in the source database.

Changing the Database Length
============================
Needing to lengthen a database is a common situation. Wanting to shorten one
is less common, but both are easily accomplished. ‘Change length’ leads to a
dialogue box with two writable icons. The first of these is used to specify
the new database length. You will be warned if, when shortening a database,
any of the records being removed are not blank. They may be deleted data,
but then again they may not. You have been warned! The other writable icon
determines the number of records by which the database will be lengthened
each time it becomes full. If this value is zero no automatic lengthening
occurs - a warning message is displayed instead.

Balancing index trees
=====================
The tree structures used to hold indices can become very unbalanced,
especially if you enter a lot of records in key-order. ‘Balance index’ leads
to a submenu with two choices: ‘Automatic’ and ‘Right now’. Choosing the
latter will optimise all subfiles in the current index. Before using it you
are recommended to examine the state of the indices with the ‘Print tree’
option.

Choosing the first menu item (‘Automatic’) enables automatic balancing of
all the indices in use every time the number of records entered becomes a
multiple of a set value. This value is initially set to 25, i.e. indices
will be balanced during record entry after each batch of 25 records, and
may be altered via submenu with a single writable item. When automatic
balancing is active the ‘Automatic’ menu choice is ticked. Clicking on it a
second time turns auto-balancing off and removes the tick. Balancing can
take some time, and the time increases with the number of records in the
file. If you are entering records from the keyboard in a fairly haphazard
sequence you should leave the ‘Manual’ option set. If, however, you need to
enter a lot of records in primary key order it might be to your advantage to
make balancing automatic whilst the database is small, returning to ‘Manual’
when a few dozen records have been entered.

The most useful application of the ‘Automatic’ option is when you are
importing records via a CSV, or similar, file. Such files frequently come
from other database systems and are very likely to have their records in
primary key order. The data import will become slower and slower as the
number of records increases and, where thousands of records are involved,
can literally take hours. Setting the system up for automatic index
balancing, say every 50 or 100 records, can markedly reduce this time.

Printing the Tree Structure
===========================
This is something you do either out of idle curiosity or to see whether an
index tree needs balancing. ‘Print index’ provides two choices:-

   (1) to print the actual keys, positioned according to the level
       which they occupy in the tree

   (2) to print only the number of nodes on each level.

The data printed applies to the current subfile of the current key and is
output to a screen window from which it may be saved in the same way as any
other list (see ‘Printing’ - Output destination).

If the tree is very deep and straggly it may not be possible to show all of
it. The maximum number of levels which can be shown is in fact 40, including
the root. Using option (1) above causes keys which cannot be displayed in
their correct positions to appear down the left hand side of the window with
a note indicating the level in which they occur.

If you choose (1), a double click with SELECT on any of the keys will
display the relevant record with the caret placed in the key field.

Duplicate primary keys
======================
Wherever possible a primary key should be chosen so as to be unique. Where
duplication of the primary key might occur the designer of the database can
decide either to allow or forbid it. (The switch which controls this is
hidden from prying eyes in the password-setting window and is thus under
‘Manager’-level control. See ‘Passwords’ for more information.) If duplicate
keys are permitted it is sometimes useful to have a list of them. Such a
list is created by ‘Find duplicates’ and may be saved as a text file.

Closely related is the final entry on the ‘Utilities’ sub-menu; ‘Warn of
duplicates’. If ticked this causes a warning message to be displayed each
time a primary key is about to be duplicated. Clicking on this menu choice
toggles the ticked state.