Acorn Risc Technologies StrongARM CD-ROM/Acorn Risc Technologies StrongARM CD-ROM.iso/software/apps/powerbase/Docs/BrowsEdit

Text File | 1995-08-21 | 26.7 KB | 542 lines

Ch 2 − Browsing and Editing

When you open a database you will normally see two windows. One of these −
the record window − displays the data record.  The other − the keypad −
contains an array of buttons for moving around the database, adding and
deleting records, searching for records etc.  It is possible to suppress the
keypad and put some or all of its action buttons on the record window itself
(see 4.2.9).  The sample database !Boxes illustrates this.  In this chapter
we will assume that you are using the keypad.

Both windows may be moved to whatever position on the screen you find most
convenient and the record window may be re-sized.  When you close the
database the position of the keypad and the position and size of the record
window are stored so that they will look the same next time you open the
database.

Most of the keypad functions have keystroke equivalents provided by the
numbered function keys (F1−F11) and experienced users might want to use
these instead of the mouse. The relevant keystrokes are given in the text
where appropriate, but note that these are default values and may be
redefined if so desired. (See Appendix B.)

2.1  Subfiles, record numbers and keys

Look at the title-bar of the record window. Three pieces of information are
displayed; the subfile number, the record number and the key of the record.
Since we will make frequent reference to these three terms it will be as
well to explain at the outset what each one means.

2.1.1 Subfiles

Suppose you have a bookshelf, capable of holding 100 books and six
partitions, numbered 0−5, which you can use to divide it into sections.  The
partitions are, to begin with, all stacked together at the left-hand end of
the shelf.  You may leave them like this if you wish and fill up the shelf
with an unbroken run of 100 books. If, however, the books fall into well
defined categories you might prefer to use the partitions to divide the
shelf up. There are no restrictions on where you can place the partitions,
or how many books can fall into each section of shelf, so long as you don’t
exceed a total of 100 books.

In a similar way every Powerbase database is able to use up to six subfiles.
When you open the database you are looking at subfile 0 and you might have
no occasion to bother with the others at all.  Like the shelf partitions
subfiles are there for you to use or not use depending on what your
requirements are.  The database remains the same size whether you use one
subfile or all six and the number of records in a subfile is limited only by
the defined size of the database.

Suggestions as to when several subfiles might be useful are given later (see
2.2.4).

2.1.2 Record numbers

Every record in the database has a number which specifies its position in a
file called Database. As you step through the records (see 2.2) you will
probably find that the record numbers shown in the title-bar look quite
random.  Record numbers reflect the order in which records were originally
entered into the database, not the order in which you see them while
browsing which is determined by the key.

2.1.3 Key

A key is a group of letters (or other characters) derived from one or more
of the data fields in a record and used to identify that record.  Of course,
the record number identifies the record in a sense but, as explained above,
record numbers are of limited use because they only reflect the order in
which the data was entered.  Keys, on the other hand, are derived from the
data itself and are stored in a special table called an index.  The keys in
the index are ordered, either alphabetically or numerically and can
therefore be used to examine the records in an order which is related to the
data.

A database may have several keys (and therefore several indices) based on
different fields in the record but there must be at least one which we call
the primary key. When you come to create a database of your own you will
find that Powerbase insists that you define the primary key before you can
use the database but subsidiary keys may be defined at any time. Whether you
use them or not is entirely up to you.

You can recognise the field which gives rise to the primary key by the fact
that its background is pale yellow instead of white like the other data
fields.*  Look at the key field and at the key itself in the title-bar and
you should be able to see that the two are related.

2.2  Moving about the database

2.2.1 Browsing

Six buttons on the top row of the keypad move you about within the subfile.
From left to right their actions when clicked on with SELECT are:−

(1)     First record   (keystroke equivalent Ctrl F1)

(2)     One record back   (F1)

(3)     10 records back − “Fast rewind”  (Shift F1)

(4)     10 records forward − “Fast forward”  (Shift F2)

(5)     One record forward   (F2)

(6)     Last record   (Ctrl F2)

The number of records forward or back for actions (3) and (4) is determined
by the number in the writable icon between the associated keypad buttons.
The terms “first”, “last”, “forward” and “backward” refer to the order of
records as determined by the keys in the index. The file wraps around so one
forward from the last record takes you to the first and one back from the
first record takes you to the last. In accordance with RISC OS conventions
clicking with ADJUST instead of SELECT reverses these actions so that ADJUST
over the first button, for instance, takes you to the last record rather
than the first. This allows you to move about the database with fewer
movements of the mouse.

The buttons at the start and end of the second keypad row resemble the Play
and Stop buttons of a tape player and it will be convenient to refer to them
by these names. Play starts an automatic run-through of the records and the
last button on the row Stop halts the process. If started with SELECT
records are displayed in forward order. ADJUST displays them in reverse
order. You may swap the order at any time by a further click on Play. The
time for which each record remains on screen may be altered by changing the
“Fast forward” interval (see above).

2.2.2 Changing keys

Two buttons in the middle of the second row of the keypad bear a symbol
resembling a key. They enable you to cycle through the available keys in
opposite directions (Shift F4 and Shift F5 respectively). ADJUST reverses
the action of SELECT. If no subsidiary keys have been defined these will
have no effect. Key fields have their descriptors (labels) a different
colour from the rest so that you can distinguish them.  By default  the
descriptor of an unselected key is blue and that of a selected key − the
currently active key − is red, but bear in mind that these colours are
user-definable (see footnote)

2.2.3 Changing subfiles

Three buttons in the centre of the third row of the keypad have the
following effect when clicked with SELECT:−

(1)     Back one subfile   (F4)

(2)     Rotate subfiles   (Ctrl Shift F4)

(3)     Forward one subfile   (F5)

(1) and (3) change the current subfile to the previous one in sequence and
the next in sequence respectively. As with the corresponding buttons for
moving from record to record Forward from subfile 5 takes you to subfile 0
and Back from 0 takes you to 5. ADJUST reverses these actions. Rotate
renumbers the subfiles so that subfile 1 is the old subfile 0 etc.  The old
subfile 5 becomes the new subfile 0. Records which were previously in, for
example, subfile 2 will then be found in subfile 3 instead. As this is quite
a drastic change you will be asked to confirm before Powerbase proceeds.

2.2.4 Using more than one subfile

A Powerbase database consists, as stated earlier, of six subfiles numbered
0-5. You may use subfile 0 (which is the one used by default) and ignore the
others if you wish, but there are occasions when users might find subfiles
very useful. If, for example, you are maintaining a set of pupil records in
a school you could assign one subfile to each year. At the end of a school
year the promotion of Year 1 pupils to Year 2, Year 2 to Year 3 etc can be
brought about by a single click on the Rotate button.

A more common use of subfiles is to use subfile 0 to hold the main records
and subfile 1 as a dumping ground for records which you want out of the way
but don’t want to lose permanently. Powerbase is used in this way in a
Further Education college where the applications file for a course is built
up in subfile 0. On enrolment day records are updated to reflect students’
actual subject choices and all records for applicants who have not appeared
are moved into subfile 1. The enrolled students in subfile 0 are then
timetabled and class lists are printed. During the first week of the course
there is a trickle of late enrolments which simply involve retrieving the
required records from subfile 1 and reinstating them in subfile 0.

The facilities for moving records, singly or in batches, from one subfile to
another are described in 2.4.2 and 2.5.6.

2.2.5 Naming subfiles

You may give subfiles meaningful names. Name subfile, from the Miscellaneous
submenu, leads to a writable menu item into which you may type a name of up
to 20 characters. This then becomes the name of the current subfile and will
be saved on closing the database.

2.3  Searching for a record

It’s all very well being able to move about the database like flipping
through the pages of a book but how do we find a specific record?  Powerbase
provides three ways of doing this; you can search for the record by key, by
record number or by using something called a filter.

2.3.1 Searching by key

The icon bearing a record card and a question mark is the Search button
(F8). When clicked with SELECT  a little window opens to the right of the
keypad. Type the key of the required record into the writable icon and
either click on Find or type Return. (To see how the key is constructed from
the key field click MENU over the record window and choose Current key. This
displays a window describing the key structure.)

If the key exists in the current index the record will be found and
displayed. If the key doesn’t exist Powerbase bleeps and displays the
nearest matching record with the key field flashing. (If the database is a
small one with keys which differ greatly from record to record then the
displayed record may not look to be very near at all.) If you typed Return
or used SELECT on the Find button the Search window will disappear. If you
want to search repeatedly it is more convenient to have the window stay on
screen and this can be achieved by clicking on Find with ADJUST. If you do
this you will notice that the icon above the Find button displays the number
of matches found.

A search carried out as described looks only at the current subfile. If you
suspect that the record you require might be lurking in some other subfile
you can force all six to be searched. This can be achieved by using ADJUST
(Shift F8) instead of SELECT on the Search button. When the search window
appears you will see that the All subfiles radio button is selected instead
of This subfile. You can change the selected radio button if you change your
mind when the search window is open.

If searching on a numeric key you will only find the record by entering a
number of exactly the right value. If the key is alphabetic, however, you
may use just the first few letters if they are sufficient to distinguish the
key from others.

There are two other buttons on the search window. Old retrieves the last key
entered (if any) and Cancel simply removes the window from the screen
without further action.

2.3.2 Searching by record number

You may type a record number, preceded by # (e.g. #1054) instead of a key.
Provided the record is in use Powerbase will find and display it, regardless
of which subfile it is in. If the record has been deleted or has never been
assigned a “Record not in use” error is generated.

2.3.3 Searching by filter

The Filter switch (Ctrl F8) is in the middle of the last row on the keypad.
Selecting it brings up the Filter window which contains a writable icon into
which you can type a search formula (see 3.3.2).  You should then click on
the Filter button in the Filter window or, alternatively, type Return. The
keypad buttons used for browsing will now only display records which match
the search formula, all non-matching records being filtered out. Deselecting
the Filter switch restores normal keypad operation.

2.4  Editing the database − fundamental operations

2.4.1 Adding new records

The icon bearing a record card and a plus sign is the Add record button
(F10). Clicking with SELECT displays a blank record for you to fill in. The
subfile number and anticipated record number are shown in the title-bar of
the record window but there is, of course, no key as yet because there’s no
data. The title-bar therefore reads “(New)”. The only field which you must
fill in is the primary key field.  Any or all of the rest (including
subsidiary key fields) may be left blank. You might find that on some fields
pressing certain keys has no effect. This will happen, for example, if you
try to type letters into a field which has been defined as Numeric.

If you type into a field which is highlighted in dark green you may get an
error message. These fields only accept certain values which are listed in a
validation table (see 5.2). To see what these values are make sure the caret
is in the relevant field then click on the List values button on the
keypad.*

After entering data into a field you can go to the next field in sequence by
pressing either Return or cursor-down⇩. To go back one field use cursor-up⇧.
These cursor keys operate so that attempting to go beyond the last field of
the record takes you to the first field and attempting to go back from the
first field takes you to the last. Pressing Return on the last field of a
record acts rather differently in that it writes the record to disc and
brings up a new blank record for editing, i.e. it duplicates the action of
the Add record button on the keypad. You can, in addition, place the cursor
in any editable field by clicking with SELECT.

When you have entered as much of a record as you wish you can click Add
record again for another blank record. The record you have just entered is
automatically written to the file. The same is true if you click on any
other keypad button or close the database altogether. You don’t need to use
the Force update (F3) button to tell Powerbase to write the record.  The
real purpose of this button is to make Powerbase save indices and validation
tables which are stored in memory. Occasional use of the button during a
long working session guards against power cuts or system failure.

2.4.2 Deleting records

The fourth row of the keypad has only three buttons, the middle one of which
has a large dustbin symbol.  This is obviously the Delete button (Shift F10)
but what are the others? The left button (F6) moves the displayed record
back one subfile, i.e. if the record is in subfile 1 it will be moved to
subfile 0.  If it is in subfile 0 it will be moved into subfile 5
(“wrap-around” again).  The right button (F7) moves the record forward one
subfile. A record in subfile 5 will be moved into subfile 0.  These buttons,
which we will refer to as Shift back and Shift forward respectively, clearly
don’t delete records at all. We often want to get a record out of our way
but keep open the option of bringing it back again and that’s where these
buttons are really useful. If you have a lot of records in subfile 0 and
want to do a clear-out you can use subfile 1 as a dumping-ground for the
unwanted records. You’re not really deleting them: just removing them from
the subfile you’re working in.

It is sometimes useful, especially when shifting a record, to be able to
“follow” it into its new subfile. You can do so by holding down SHIFT while
you click on the Shift forward or Shift back button.

The Delete button should only be used when you are sure you want to lose the
record permanently.  As this is quite a drastic action Powerbase will ask
you to confirm it before the record actually disappears.

2.4.3 Altering existing records

A displayed record may be altered manually without any restrictions other
than those applying to the addition of new records (see 2.4.1). You will be
asked to confirm an alteration which would result in a change to the primary
key. The normal RISC OS conventions for editing writable icons apply, e.g.
Ctrl U to clear the icon. As with new record entries you need do nothing to
make Powerbase save your changes to disc − the process takes place when a
different record is displayed, when a database is closed or when you quit
Powerbase.

2.5  Editing the database − special features

2.5.1 Undoing mistakes

Changes to the record on-screen can be undone provided you haven’t clicked
on Force update (not normally needed anyway) or done anything to cause
Powerbase to display a different record. In other words, you can undo
changes made to the current record as long as it remains on the screen. You
may either undo all the alterations made to the record or only those
relating to specific fields.

If you bring up the main menu and choose Undo changes the record will be
returned to the state it was in when you displayed it and before you began
to edit it. To restore an individual fields, click MENU over the field then
go to the Field submenu and choose Undo changes from there.

Only ordinary writable fields and check boxes may be restored; you can’t
restore External fields (see 2.6) which is why a warning is normally issued
before deleting such fields.

2.5.2 Using a template

You may want certain fields to be filled in with fixed contents on every new
record to save typing the same thing every time and Powerbase provides a
means of doing this. Call up the main menu, go to the Miscellaneous submenu
and choose Edit template. A blank record is displayed and the window title
says “Enter data which you wish to appear by default on new records”. Type
in the required fixed data then click any of the usual keypad buttons. You
will now find that the “blank” record displayed every time you click Add
record isn’t really blank at all but already contains the data entered in
your template. Note that this feature affects new records only. It doesn’t
have a retrospective effect on existing records.

2.5.3 Using the clipboard

The buttons at the far left and right of the third row of the keypad may be
thought of as Copy to Clipboard (Ctrl C) and Paste from Clipboard (Ctrl V)
respectively. They can save a lot of time when you want to copy data from
one field into another. When you click SELECT on Copy the contents of the
field which owns the caret is stored in memory. Positioning the caret in
another field and clicking on Paste will copy the stored data into the new
field. If the data is too long for the field it will be truncated.

Copy and Paste are not limited to copying into another field of the same
record; you may use them to copy data between records or from a record into
a validation table or a dialogue box or, indeed, between any two writable
icons within Powerbase. Data remains on the clipboard until you use Copy
again.

2.5.4 Choosing the field where editing starts

When an existing or blank record is displayed Powerbase places the caret in
the first (i.e. lowest-numbered) writable field of the record. This might
not necessarily look like the first if the fields have been placed in
out-of-sequence positions in the window.

When going through a database making changes to one or two fields somewhere
in the middle of the record it might be convenient to have the caret start
somewhere else. Click MENU over the field where you wish the caret to start,
go to the Field submenu and choose Start editing. When a record is displayed
the caret will be placed in the chosen field. The same procedure is used to
restore the normal starting position.

2.5.5 Changing many records at once

To alter a given field in a set of records point the mouse at the field and
click MENU. Go to the Field submenu and choose Global changes. In the first
writable icon (Replace) enter what you want changing and in the second
(with) enter what you want the field changing to. In the third enter a
search formula specifying which records are to be changed. (See 3.3.3 and
2.3.3) and click on Change or type Return.

Note the following:−

•       Only records in the current subfile are affected.

•       Replacement only occurs if the new data will fit in the field.

•       Leaving Replace blank causes the target field to be replaced in any
record which matches the search formula, otherwise replacement occurs only
where the existing field matches the Replace string.

•       Leaving with blank causes the target field to be blanked in records
which match the search formula and in which the target field matches the
Replace string.

•       Leaving the search formula blank causes replacement to occur in all
records of the current subfile for which the target field matches the
Replace string.

It should be apparent from the above that leaving both Replace and the
Search formula blank will place the with string in all records of the
current subfile.

The characters “$” and “#” may be used as “wild-card” characters in the
Replace and with strings.  The first of these is used to represent a group
of characters which don’t need to be matched.  If you:−

Replace $Street with $Road

the substitution will be performed on any record which matches the search
formula and where the target field ends with “Street”. The ending will be
changed to “Road” leaving the rest of the string unchanged.  Another example
of use is:−

Replace 47$ with 1047$

If the target field begins with “47”, the beginning will be changed to
“1047”. The rest of the field will be unaltered:−

Replace $MPUT$ with $NFUS$

would change “MPUT” occurring anywhere in the target field into “NFUS”, e.g.
COMPUTER would become CONFUSER.  You may, of course, use “$” in the middle
of a word:−

Replace re$ment with dis$ed

would cause a string in the target field beginning with “re” and ending with
“ment” to have its head and tail replaced with “dis” and “ed”, leaving the
middle unchanged. e.g. “replacement” would become “displaced”.

The “#” character is used to represent a single wild-card character and can
replace individual letters in specific positions. The Replace and with
strings must be the same length and should have “#” characters in the same
positions. The characters in the remaining positions are the ones which get
replaced, but only if they occur in the corresponding positions of the
existing field value.

You may also use Global changes to perform  simple calculations e.g. “+12”
will add 12 to the current value in the field on all the matching records.
“*5-13” will multiply the current value by 5 and then subtract  13. It is
operations like these which are most likely to produce values which won’t
fit in the field, especially if floating-point numbers are involved. The
operation isn’t limited to Numeric fields, or even to other types of field
consisting wholly of numerals; Powerbase will find the number embedded in an
entry such as “ABC45XYZ” and the operation “+12” would convert it to
“ABC57XYZ”.

2.5.6 Deleting many records at once

Choosing the Move/delete choice on the Miscellaneous submenu opens a window
which displays the same three icons as those on the Delete, Shift forward
and Shift back Buttons. Here, however, they are merely for identification.
It’s the radio buttons beneath them determine what will happen to the
records, and the default setting is for Shift forward. Type a search formula
(see 3.3.3 and 2.3.3) and click Move or type Return. All matching records in
the current subfile will be moved or deleted as specified. A fourth choice
allows you to choose from all subfiles records which match the search
formula and collect them together into a single, specified, subfile. For
example,you could use this option to send a specified set of records to
subfile 2, another to subfile 3 and so on. If you have records distributed
throughout the subfiles you could also gather them all together in subfile
0.

Operations from this window may be undone (to one level only) by clicking on
the Undo button.



2.6  External fields

The data in External fields is not stored within the Database file but in
separate files, one for each record, stored inside the database’s
application directory. These files may be Text, Sprite or Draw files and can
be linked to buttons on the record screen.  Clicking on these buttons loads
the external file into Edit, Paint or Draw (provided that the relevant
program has been “seen” by the filer.

It is also possible to link Text files to a Text block field which will
actually display the text (with certain limitations) within a large icon.
Sprites may be similarly displayed in a Picture field.

2.6.1 Linking files to the fields

To link a file with an External field drag the file’s icon onto the record
window and drop it on the appropriate field. For example, if the record
includes a field represented by a Text button, i.e. one bearing a small
version of the Edit icon, you may drop a Text file onto it. The button’s
icon changes to the small version of the Text file icon to indicate that the
file has been linked. Sprite and Draw files are linked in the same way and
Powerbase will not allow the wrong type of file to be linked. A Text block
field may also have a Text file dropped onto it.* The text (or as much of it
as will fit inside the icon) is then displayed on the record window.  The
formatting will not be the same as if you examine the text in Edit; lines
are word-wrapped and centred within the display icon. This is a feature of
multi-line RISC OS text icons. You can’t edit the text directly but it is
possible to export the file for editing (see below). Sprite files may be
dropped onto and displayed in a Picture field. Any new file dropped onto an
External field which is already linked to a file simply replaces the old
file with the new.

2.6.2 Editing External fields

You can’t edit an External field directly, only via an appropriate editing
program such as Edit, Paint or Draw. As long as the editor has been “seen”
by the filer clicking on the on-screen button with SELECT will load the file
into the editor and display it. You can edit the file and re-save it without
altering its name and it will remain associated with the same field of the
record.  Text block and Picture files are loaded into their editors by a
double click.

2.6.3 Clearing and exporting field contents

Clicking MENU over an External field makes available certain entries on the
Field submenu which are shaded for other types of field. Clear contents lets
you delete the linked file from the database application. As deleting a file
is rather drastic you would probably like to be warned when this is about to
happen so the message “Delete object? Are you sure?” normally appears.
Finally, Save contents on the Field submenu lets you export the linked field
to a filer window or to another application.