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EASY BASE NETWORKING GUIDE Contents
Introduction Page 1
Batch Starting Page 3
Clearing Locks Page 4
Configuration Page 6
Development Work Page 7
File Open On Server Page 9
Lock Directory Page 10
Numbering Records Page 11
Private Keyword Page 12
Protective Locking Page 13
Self Locking Loops Page 16
Strategic Locking Page 17
Terminal Number Val. Page 18
Unique Entries Page 19
................................................................................
Introduction
Introduction
Easy Base Networker has been designed to make the creation of
multi user data management systems as simple as possible. To do
this it incorporates automatic locking and privatisation
routines. With a few exceptions, you can create multi user
systems just as if you were writing for a stand alone PC.
The few exceptions are, however, important so please read this
short guide before attempting to convert any single user
application.
Because Easy Base is an interpreter, the same program is used
both for the creation of your application and for running it.
Only the running routines are multi user. Multiple work
stations can access the same forms and procedures
simultaneously only when such forms and procedures are called
from pre defined user menus. Multiple work stations can access
the form and procedure design routines (System Menus) provided
they are each doing design work in different data sub
directories. No two work stations can access the system menus
for the same data sub directory at the same time.
Terminology used in this Guide.
PUBLIC FILES:
Files to which all work stations have access. The public files
are form definition, data and procedure definition files
together with the network common configuration file.
PRIVATE FILES:
Files for which each work station has its own copy. The private
files are: user menus, terminal configuration, procedure output
subindex and temporary forms. You can also write to private
copies of public form definitions for temporary storage by
using the keyword "Private".
TERMINAL NUMBER:-
This is a unique number assigned to each work station logged on
to Easy Base. The terminal number is used in the naming of the
work station's private files and for recording which work
station has placed any access lock.
SYSTEM LOCKS
The locks which Easy Base engages to prevent simultaneous
loading and simultaneous access to the system menus in any one
data sub directory.
PROTECIVE LOCKS
The locks which Easy Base engages to prevent index file
- 1 -
................................................................................
Introduction
Introduction
corruption during multiple access.
STRATEGIC LOCKS
The locks you set in procedure code when you require a form to
be locked for non protective reasons.
Easy Base Networker was developed under Novell Personal
Netware. It does not, however, contain any Novell specific code
and should be reliable on any DOS based network system.
To get started, install Easy Base to a new directory on a
server. Allocate a drive letter for your work stations to
reference this directory and set your network software to allow
unrestricted read and write access to all files in that
directory and all sub directories under it.
To log on to Easy Base, three parameters are required. The
terminal number to use, The data sub directory to operate in
and a password for either the system menus or a user menu.
From a work station, change to the drive you have allocated and
type "EB".
When you start Easy Base with the command EB you will be asked
to supply the three parameters which it requires. All three
parameters can be supplied automatically either by setting them
in the environment ( Work stations which self boot ) or by
placing them on the command line. ( See Batch Starting )
All locking in Easy Base is by "Soft lock". DOS file and record
locking techniques are not used. With any locking strategy,
locks can be left engaged if a work station suffers a power
failure or is switched off without exiting the program. System
and Access locks which are left engaged after a power failure
can be cleared by Easy Base or by DOS file erasure.
(See Clearing Locks )
Applications written in previous stand alone versions of Easy
Base can be copied directly to a sub directory of Easy Base
Networker. However, the pre processed (.PPR) files created by
Version 9 are NOT compatible with Network V1 and must be erased
before use. You can erase all .PPR files by selecting
Relationships from the main system menu. The system values
Total Records, Total Copies and Current Record no longer exist.
Any procedure which uses these values must be changed. They are
now available as pseudo fields Form.Total Records, Form.Total
Copies and Form.Record Number.
- 2 -
................................................................................
Batch Starting
Batch Starting
You can by pass entering any or all of the sign on parameters
either by setting them in the environment of the work station
or by supplying them on the command line.
To have a work station automatically log on as terminal 1 in
the sub directory accounts with the password "Fred", add the
following lines to the work station's Autoexec.Bat file:-
SET EBT=1
SET EBD=ACCOUNTS
SET EBP=FRED
Or start Easy Base with the command line :-
EB T=1 D=ACCOUNTS P=FRED
Any parameters which are not supplied either in the environment
or on the command line will be asked for on start up.
If you have set the start up parameters for any given work
station in the environment and you start Easy Base with
different parameters on the command line, the parameters on the
command line override those in the environment.
If your application has different passwords for different menu
structures you can set the terminal number and directory and
leave the user to supply the password.
If the user has access to different directories then just set
the terminal number and the user can choose the directory and
enter the password.
NOVELL WARNING
If you save a "Login Script" after setting EB environment
variables and subsequently change the settings in your
Autoexec.bat file, Novell will swap the setting it saved for
the new ones whenever you login. Saving a new Login script
after the change does not rectify the situation. You actually
have to find the login script file and edit out the old
environment settings. Under Novell Personal Netware this file
is called PNWLOGIN.SCR and is stored in a numbered sub
directory under C:\NWCNTL\MAIL
- 3 -
................................................................................
Clearing Locks
Clearing Locks
ACCESS LOCKS
If a data access lock is left engaged it can be cleared by
selecting "Clear Access Locks" from the utilities menu. You can
also make "Clear Access Locks" available on user menus.
When you run "Clear Access Locks" Easy Base clears all access
locks in the current data sub directory. Because it clears ALL
locks in the current directory you should ensure that no other
work stations currently require locks in place - ie they should
not be running procedures or adding or modifying records. There
is no need for them to log out of Easy Base.
SYSTEM LOCKS
Easy Base uses two system locks - a loading lock and a System
Menus lock. Because of the way Easy Base initially loads its
overlays, no two work stations can load at the same time. When
a work station attempts to load Easy Base while another work
station is loading, Easy Base displays the message "Please wait
another terminal is loading". As soon as the first work station
has logged on this message will clear and the second will load.
If the first terminal suffers a power failure while loading,
this lock will be left engaged. If the loading lock does not
clear within one minute, The "Please wait" message displayed on
any other work station which is trying to load is replaced with
one which allows the user to escape and enter the reset
command.
To clear the loading lock type "EB reset" at the command
prompt.
Whenever a work station is accessing the system menus for any
given data sub directory, all other terminals are locked out of
the system menus in that directory. If a work station is
powered off without leaving the system menus then this lock
will be left engaged and no work station will be able to access
the system menus for that directory. The system menu lock is
also cleared by typing "EB reset" at the command prompt.
WARNING
It is essential to your data integrity that no two work
stations log in to Easy Base with the same terminal number. To
prevent this Easy Base maintains a log of which terminal
numbers are in use. This log is erased when you issue the
command "EB reset". If one or more terminals are logged on to
Easy Base and another issues the command "EB reset" then it
will be able to log on with a terminal number which is already
in use. You must prevent this as the two work stations with the
- 4 -
................................................................................
Clearing Locks
Clearing Locks
same terminal number will overwrite each others private files
and ignore each others data access locks with unpredictable
results.
If you have arranged for each work station to supply its
parameters from the environment or from the command line in a
batch start this is not a problem, but if you allow work
station operators to choose their terminal number it is.
To be absolutely sure, you should ensure that all work stations
exit Easy Base before issuing the "EB Reset" command and log
back in after it.
DOS LOCK CLEARING
All Easy Base locks can be cleared manually by erasing the
locking files. The locking files are:-
Loading Lock EB.LOD Easy Base Directory
System Menus Lock EB.LOG Easy Base Directory
Directory Lock DIR.LOC Data Directories
Form Locks Base(No).LOC Data Directories
- 5 -
................................................................................
Configuration
Configuration
The utilities Install Printer, Options, Screen Colours and Set
Paper Length described in the programmers reference are
combined under "Configuration" on the main menu in the network
version of Easy Base. You can also add configuration to a user
menu.
Apart from date and numeric formatting, all configuration items
are private to the terminal being configured. You can therefore
install different printers on different workstations. When you
install a printer in Easy Base you only have the option to send
output to LPT1 or LPT2. When you select an LPT port the output
will be sent either to a printer connected to that port or to a
network printer that has been mapped to it by your network
software.
CAUTION:
Novell netware reports three LPT ports on all workstations even
if they only physically have one. If you set output to LPT2 and
your workstation has no physical LPT2 and no network printer
has been mapped to LPT2 then Easy Base will hang up when you
try to print.
When you change the network common items, date and numeric
format. They only take effect on other workstations from the
next time they log in.
- 6 -
................................................................................
Development Work
Development Work
When you are doing development work from the system menus there
should not be any other operator accessing forms or procedures
in the data directory you are working in. This does not mean
that you cannot have a second workstation accessing that
directory under your control. It is in fact preferable to have
a second workstation for testing purposes. There are aspects of
design work that Easy Base does not and in some cases cannot
provide locking for. This section will explain how to avoid
conflicts.
The only system operations which are fully protected are Data
entry from the system menus and packing forms. You can perform
these operations safely even when other operators are active.
Whatever system operation you perform, there will be no
conflict if the other active workstation/s are at rest
displaying a user menu.
To make and test modifications to an application, provide
access to the system menus from your user menu and start your
application on the user menu for both workstations. One
workstation can then access the system menus while the other
remains on the user menu.
After modifying a form or procedure you can then escape to the
user menu and test the modification in a multi user
environment.
Modifications to forms, relationships and procedures are
effective immediately. Modifications to User Menus, Vat rates
and network common configuration items take effect the next
time a workstation logs on or changes directory.
If, for example, you change your user menu structure then you
must select Change data directory and select the same directory
again before it is displayed.
If your application is in constant use, you can minimize down
time by making and testing your modifications in a spare
directory with a copy of the App. Once you are happy, other
users only have to be shut down while you make the
modifications in the live directory and not while you do your
testing.
If you absolutely have to make modifications without shutting
down other workstations then there is only one operation which
can actually corrupt your data. That is if you modify a form
such that its record length changes. You MUST NOT do this while
any other workstation is in data entry to that form or is
running a procedure which updates that form. The other work
station will continue using the old record length and corrupt
the data file. All other operations may or may not cause
- 7 -
................................................................................
Development Work
Development Work
spurious system errors on either your workstation or one of the
others but will not normally affect data.
Whenever you add modify or delete forms, procedures,
relationships, choice lists or user menus Easy Base erases and
re writes the definition file and the form, procedure or choice
list directory file. Any workstation which attempts to read
from a file between the erase and re write will crash, and your
workstation will crash if it actions the erase while another
workstation has the file open.
- 8 -
................................................................................
File Open on Server
File Open on Server
If a workstation fails and it had files open at the time, then
your network server will prevent any other workstation from
erasing those files before the failed workstation logs back in
to the network.
There are several processes in Easy Base which erase files.
These are, packing, the procedure commands "clear records from"
and "rename temp as" as well as form, relationship and
procedure modifications from the system menus.
If any workstation suffers a power failure while accessing Easy
Base you should re start it and log back on to the network as
soon as possible. If the failed workstation did not have files
open at the time of the failure then other workstations will
continue to work normally. If it did have files open then any
workstation which tries to erase one of those files will crash
with a "File Open on Server" message.
Any such errors will cease as soon as the failed workstation
logs back on to the network. If the failure was such that the
failed workstation cannot be restarted then you must shut down
and restart the server.
During most activity in Easy Base, it is unlikely that a
workstation failure will cause problems. There is one major
exception to this. That is if a workstation fails while packing
a form.
If a workstation fails while packing a form, Easy Base will
restart the packing process automatically the first time any
workstation logs on to that data directory. If the failed
workstation has not logged back in to the network then any
other workstation logging on to the data directory will crash
with the "File Open on Server" message. In other words, no
workstation will be able to access the data directory until
either the failed workstation is back on the network or the
network server has been restarted.
You may also get a "File Open on Server" error if any other
program such as a fileviewer opens an Easy Base file.
- 9 -
................................................................................
Lock Directory
Lock Directory
When you need to make modifications to an application you can
prevent other workstations from logging on to the directory you
are about to modify by selecting "Lock Directory" from the
utilities menu. If any other workstations are active in the
directory when you select Lock Directory, Easy Base will list
their terminal numbers on screen. When all other workstations
have logged out of the directory the lock will engage.
When you have finished your modifications select "Clear Access
Locks" to clear the directory lock.
Apart from application modifications, the directory lock should
be used before backup, restore or data import routines.
Once a directory lock has been set, only a workstation using
the terminal number which set it can access the directory.
- 10 -
................................................................................
Numbering Records
Numbering Records
If you are converting a single user application then you may
have to adjust your code where records are entered via a
procedure and each record has to have a consecutive number in
one of its fields.
In single user applications record numbering is often done by
having a "Last" form which holds a single record with the last
record number in it. The procedure which enters new records
derives the next record number in a field on its input screen
with the derivation :- Lookup(Last,Number) + 1 and the
procedure code updates the last form :-
For Last
Last.number = input.number
Update record
Next
In a multi user environment this is not reliable. If another
workstation starts the procedure after yours has done the
lookup but before you run the procedure then both workstations
will derive the same number on screen.
To ensure correct numbering your procedure code must re-check
the Last.number value when it is run.
For Last
input.number = last.number + 1
Last.number = input.number
Update record
next
Although this will ensure correct numbering, it may be
off putting to see the same record number on two screens. To
avoid this you can declare a variable to pick up the number in
and delete the input.number field. The code would then be:-
Declare variables
number as number
end
for last
number = last.number + 1
Last.number = number
Update record
next
For form new record
form.number = number
copy all from input
next
- 11 -
................................................................................
Private Keyword
Private Keyword
One of the main differences between stand alone and multi user
applications is that where a form is used for temporary storage
each workstations temporary records must be kept separately.
For example, in an order taking application you might have one
procedure which looks up stock items and enters them to an
"OrderItems" form. When all the items have been entered another
procedure prints out the order and clears down the "OrderItems"
form. If these procedures are to be used by more than one work
station then, clearly, the items entered by one station must be
stored separately from those entered by another.
In many data management systems this would involve separate
forms and procedures for each work station. In Easy Base you
can separate data by placing the keyword "Private" at the end
of any for loop and at the end of the "clear records from"
command.
In this example the following procedures can be used by any
number of work stations to create separate orders using the
same procedures and OrderItems form.
For OrderItems new record private
Copy all from input
Next
.........................................
For OrderItems private
Total = Total + orderitems.price
print list items
next
Print report footer
.........................................
Clear records from OrderItems private
As an aid to debugging you can view the records which have been
entered privately for any workstation by pressing Ctrl + P when
in data entry to the form.
CAUTION
The provision of private data files is for temporary storage in
applications like the one described above. It is not suitable
for keeping permanent private records. There are no facilities
for packing or reformatting the private data file. Private
records can only be removed with the "Clear records from form
private" command in procedure code. If you modify a form which
has private data records the private data is not reformatted to
the new form definition and the old data must be erased with
the "Clear records from" command before use.
- 12 -
................................................................................
Protective Locking
Protective Locking
The Easy Base protective locking allows any number of work
stations to read or write to data files simultaneously where no
index file is involved. It allows any number of workstations to
read via the same index file simultaneously but prevents any
workstation from writing to an index file that is being read
from. It prevents simultaneous writing to the same index file
and any file from being erased while in use.
Whenever a workstation attempts a process that is locked by
another work station Easy Base waits for the lock to be
released. If the lock is not released within four seconds Easy
Base displays the message "Waiting for Access - Esc Cancel". If
the user presses the escape key with this message on screen,
the process is cancelled. If the process was in data entry to a
form the workstation remains in data entry to that form and is
ready to accept any other input. If the process was during a
procedure then the procedure is terminated. If it had a
repeating input screen, control returns to the input screen and
if it did not, control returns to the menu from which it was
called.
The protective locking routines in Easy Base are automatic
apart from two options.
1. In certain procedures you will not wish to allow the user
the option to cancel the procedure when he has to wait for a
lock to clear. To do this, place the command "Wait" in the
procedure code after output field and variable declarations.
If the command "Wait" has been issued and the procedure
encounters a lock which lasts more than four seconds then Easy
Base still displays the message "Waiting for Access" but the
escape key is not active.
2. Easy Base provides two options for locking while a procedure
reads records using an index file. Consider the code:-
For Customers with Surname in order
Print list items
next
For this procedure to complete successfully, no other work
station must write to the index file on Surname during the
procedure. If there are many records in the customers file and
the output is being sent to a printer then other workstations
could be prevented from adding modifying or deleting records in
the customers form for some considerable time.
As well as reading directly from the Customers.Surname index
Easy Base can also make a private copy of the index file as it
stands at the start of the procedure. The Customers form is
locked only for as long as it takes to make the copy. Once the
- 13 -
................................................................................
Protective Locking
Protective Locking
file has been copied, other workstations are free to write to
the customers form and the procedure selects records using its
private copy of the index file.
By default, Easy Base locks the form against write processes
during the procedure. To take the private index option add the
command "No Lock" to the end of the "For" line.
For Customers with surname in order no lock
There are pros and cons for both methods and the exact nature
of your application will determine which should be used in any
given for loop.
The default system prevents writing to the form for the
duration of the loop but has no anomalies in the output. The
copy index method locks the form for the minimum time, but if
the indexed field of any record is altered by another
workstation the altered record may be processed out of order.
For example, in this loop, if another workstation changes a
customers surname from Smith to Jones before the procedure
reaches the Smiths, you will have a Jones listed among the
Smiths in your printout because that is the record's position
in the private index.
The "No Lock" option should only be applied to for loops of
public files. It should not be applied to any loop which is
already private. :-
PickList, Temp, any loop using the private keyword and any loop
using a subindex are automatically private.
EASY BASE AUTOMATIC LOCKING SUMMARY
File Erasure (Packing, Clear records from, Rename temp as) :-
None of these processes will start while any other workstation
is accessing the form to which they apply. Once they have
started, no other workstation can access the form until they
are complete.
Data Entry to forms :-
File erasure is not permitted at any stage. Write locking is
engaged during an F3 search on an indexed field and while any
other workstation makes a lookup from one of the forms indexed
fields. Read and write locking is engaged during F2 add or
update record and during F7 delete record.
Procedures :-
In procedures, locks are set separately for each "For" loop.
- 14 -
................................................................................
Protective Locking
Protective Locking
When loops are nested, the locks set by each loop are retained
until the procedure exits the outermost loop when they are all
cleared together.
Loops of Picklist, Temp, Subindex and any loop using the
private keyword have no locking as the files involved are
private to the workstation.
Unqualified loops ( For Form ) Lock against file erasure only.
Loops qualified by "With" set a write lock on the form. Loops
qualified by "New Record" or containing the commands "Update
record" or "Delete record" lock the form against read or write.
A loop prefixed by "Index Off" follows the same rules as for
Packing. It will not start while any other workstation is
accessing the form and once started, no other workstation can
access the form until it is finished and the indexes are
rebuilt.
- 15 -
................................................................................
Self Locking Loops
Self Locking Loops
When For Loops of the same form are nested in a procedure Easy
Base ignores any lock which the workstation has set for the
outer loop when it starts the nested one. It does not ignore
any lock set by another workstation. It is therefor possible to
write a procedure which cannot be run on two workstations
simultaneously because they will each lock each other.
For parts with number = input.number
for parts alias addone new record
copy all from parts
Addone.number = jointext(input.number,"a")
next
next
Although a legitimate procedure in a single user environment,
this will self lock if run on two workstations. The first line
sets a read only lock on the parts form. A single workstation
will ignore its own lock and write the new record but if two
workstations run the procedure neither will be able to write
the new record until the other releases its read only lock.
Such procedures are seldom necessary and when they are you can
avoid the problem by making the read only lock the inner one.
For parts new record
for parts alias getone with number = input.number
parts.name = getone.name
parts.Qty = getone.Qty
parts.number = jointext(input.number,"a")
next
next
Although the convenience of using "Copy all from" has been lost
this procedure will not self lock. The outer loop now locks
read and write access to the parts form so any other work
station attempting to run the same procedure cannot start until
this one has finished.
- 16 -
................................................................................
Strategic Locking
Strategic Locking
Strategic locks are locks which are not covered by the
automatic protective locking but are none the less necessary
for the correct operation of an application.
Strategic locks are set by the procedure command Lock and
cleared by the command Unlock. Strategic locks will not engage
while any other workstation is accessing the form to be locked
and once set prevent any other workstation from accessing the
form before the Unlock command has been issued.
Each Lock command must have a matching Unlock command but they
need not necessarily be in the same procedure. If a form has to
be locked while several procedures run from a batch menu, for
example, then the first procedure can lock the form and the
last can unlock it.
Strategic locks are seldom required in applications which
simply store and report on data. In transactional applications
however, they are often essential.
As an example, a form "Work" contains records of the hours
worked by employees - one record for each time each employee
clocks in. Each record also has a number field and procedures
which enter records to the form derive the record number field
from a form "Last" which contains a single record with the last
record number in form "Work".
When a single employees records are deleted from the form, the
form is packed, the records are renumbered and the entry in the
"Last" form is updated with the new number of records in "Work"
The Easy Base protective locking will prevent any other work
station from entering a new record during the deletion loop and
during the pack. It will not prevent it from entering a new
record between the deletion loop and the pack or between the
pack and the updating of the "Last" form. To ensure that no
other workstation adds a new record to work before the "Last"
form is updated the "Last" form must be locked throughout.
Lock Last
For Work with employee = input.employee
Delete record
Next
Pack Work
For Last
For Work
x = x + 1 : Work.number = x
Update record
Next
Last.number = x : Update Record
Next
Unlock Last
- 17 -
................................................................................
Terminal Number Val. Terminal Number Val.
The System value "Terminal Number" is available in field
derivations and procedure code and returns the terminal number
used to log on to Easy Base.
The main use of the Terminal Number value is to privatize
lookups in temporary storage forms. As an example, an invoicing
system might have one procedure which looks up a customers
number from the "customers" form and looks up the next invoice
number from the "last" form. It then enters a record in the
"current" form so that the next procedure, which looks up stock
items and enters them privately to the "invoicelines" form, can
automatically lookup the "Current.Customer" and
"Current.invoice".
If multi workstations are to use these procedures at the same
time then each must be able to lookup its own Current.Customer
and Current.Invoice. To do this, in say a six terminal
application, six records are pre entered to the "current" form
with the values 1,2,3,4,5 and 6 in the terminal field.
The first procedure has the code:-
Declare variables
No as number
end
for last
No = last.invoiceno + 1
last.invoiceno = No
Update record
next
for current with terminal = terminal number
current.customer = input.customer
current.invoiceno = no
Update record
Next
The procedure which enters the invoicelines has a hidden field
"Terminal" derived :- Terminal Number and looks up the current
invoice number and customer based on a relationship linking
this field with the terminal field in the "Current" form.
The Terminal Number value can also be used to create private
entries in public forms. If a public form "Notes" has a field
"Terminal" and each workstation enters its notes together with
its terminal number then the procedure:
For Notes with terminal = terminal number
Print list items
next
Will only print the notes entered by the workstation running
the procedure.
- 18 -
................................................................................
Unique Entries
Unique Entries
Where new records are entered to forms via procedures and one
of the fields in the form must be unique, the procedure must
test to see if the value it is about to enter in the unique
field already exists. In single user applications this test can
be accomplished solely on the input screen.
To check a unique field "Name" in form Parts the input screen
name field would be derived:-
If(lookup(parts,name) = name,blank[beepPart Name Exists !Cursor
name],name)
In a multi user environment this is no longer reliable. If two
workstations enter the same name on their input screens at the
same time they will both pass the lookup test above. To ensure
a unique entry you must re check if the value exists at the
start of the procedure code and return to the input screen if
the value has been taken since the field was filled.
Declare variables
x as number
end
For parts new record
for parts alias checkit with name = input.name
x = x + 1
next
if x > 0 then
beep
Display Status "This part name already exists !"
Delay 2000
Recall input screen
end if
copy all from input
next
When the line "For parts new record" is processed, the parts
form is locked so no other workstation can add a record. If the
name does not exist then the procedure adds the new record but
if it does the operator is warned by the beep and status
display and the procedure returns to the input screen without
adding the new record.
- 19 -
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