posted May 27, 2004 09:20 PM            

"Lothar Pink" Rocks!!!

I'm gonna name my next son that

posted May 28, 2004 12:23 AM            

Relating to databases, you don't start building something as
complex as the Empire State buiding until you have built your
share of humble dwellings with simple tools. And building
anything means dealing with problems in design and planning
as the occur to you.

The answers concerning locks and sharing were good ones, and
these involve the OPEN statements when you access files. When
you CLOSE a file you release it so that some other client can
then access it. To improve efficiencies, it is common to
SHARE files when the users only need read access to the content,
and are not planning on making changes. A LOCK is only needed
if the contents of the file are expected to be changed by a
write operation. This prevents other users from getting a mix
of information that consists of a partial record change, which
would then be incorrect.

However, it is really unnecessary to try and build a whole
database from scratch, since there are many available databasing
products that PowerBASIC can interface to which will take care
of the untidy details for you. For one thing, most support
record locking instead of whole file locking, which lessens the
chances that the same users will be in conflict with each other.
Some use a journal of changes, so that you can roll back at any
point if a transaction is incomplete, such as the network goes
down or a machine fails while a change is underway. A history
file also can be used to verify what changes were made and who
made them - an important consideration when it comes to
validating any changes made later on.

Many of the available databases are free, and some include good
examples of how to link up to them through your own program.
Usually, these examples cover the use of simple script files,
VB, C, Pascal, and similar examples that can easily be adapted.

The most powerful databases are generally the relational ones.
This just means that all the data is not placed in a single
database, but in related databases. You can add new databases
without effecting the original ones as new needs and more data
comes into being. The relationships between the different
databases is described in a series of templates, so as you add
new databases, you modify or extend the range of templates.

A big push is to try and access relational databases with a
relational language, of which SQL (Standard Query Language) is
probably the best known. Database users learn SQL, then they
can work with any database that supports the language, and there
are many. You can also program these databases externally by
the use of SQL, meaning just sending the right commands as
though you were a user.

So my suggestion is to consider getting familiarized with a
relational database, preferably one that supports SQL, and
once you have actually used it to set up your database, you can
consider either automating tasks with its built-in language,
or of trying to manipulate it with a separate program written
in your programming language of choice. MySQL is a good free
one, from the reports I've read. One that is often available
in an office that uses Windows is Microsoft's Access. Access
is probably the preferred choice up to about 25 users.

Keep in mind that originally, you only need to focus on the
single user aspects of setting up and using the database. As you
identify who the other users are, and what their roles will be,
you can focus on how the database is to be administered and what
rights each person or PC is going to be allowed.

I have seen some discussions on working with various databases
using PowerBASIC, so don't give up on the idea of doing more
research and reading on the topic.

It is much easier to contemplate working with a database if you
approach the problem by steps, and not leap at the whole thing
without focusing on what needs to be done first. And there is
no reason you cannot attempt a course on the subject - perhaps
one of the free online courses that you can find with a search.
These will take you through the elementary steps of setting up
and using your first database.

posted May 28, 2004 02:08 AM            

Product comes as:

api
.net
asp
com
ole db
vcl

Gian

posted May 28, 2004 03:25 AM            

------------------
Last night i was decided to retreat, Then i decided not to.

posted May 28, 2004 04:50 AM            

quote:

---

Originally posted by Elias Montoya:

I didnt found info for the last one

---

VCL = Borland Delphi component (sort of PB's *.PBU)

Knuth

posted May 28, 2004 05:22 PM            

#DIM ALL      'lock, get, put, unlock
FUNCTION PBMAIN AS LONG
  DIM hFile&,Fname$,RecordLength&,RecNum&,Attempt&,MaxAttempts&
  DIM Buffer$,RecordsToWrite&,ByteNum&
  maxAttempts& = 10
  RecordLength& = 20
  RecordsToWrite& = 1
  DO
    ERRCLEAR
    hFile& = FREEFILE
    fName$ = "DATA.TXT"
    OPEN Fname$ FOR BINARY LOCK SHARED AS #hFile& LEN = recordLength&
    IF ERR THEN
      INCR Attempt&
      SLEEP 100
    END IF
  LOOP UNTIL ERR = 0 OR Attempt& => MaxAttempts&
  
  IF Attempt& => MaxAttempts& THEN
       MSGBOX "Can't open" & STR$(ERRCLEAR)
       GOTO ExitProgram
  END IF
  Attempt& = 0
  DO
      ERRCLEAR
      LOCK #hFile         'lock entire file
      IF ERR THEN
        INCR Attempt&
        SLEEP 100
      END IF
  LOOP UNTIL ERR = 0 OR Attempt& => MaxAttempts&
  IF Attempt& => MaxAttempts& THEN
      MSGBOX "Unable to lock file" & STR$(ERRCLEAR)
      GOTO ExitProgram
  END IF
  buffer$ = SPACE$(RecordLength&)
  FOR RecNum& = 1 TO RecordsToWrite&
    ByteNum& = LOF(#hFile) + 1
    LSET buffer$ = STR$(RecNum&) & "YOUR DATA"
    PUT #hFile,ByteNum&,buffer$
  NEXT
  FLUSH  #hFile
  UNLOCK #hFile
  MSGBOX "Bytes in file" & STR$(LOF(hFile))
  CLOSE #hFile
ExitProgram:
EXIT FUNCTION
ErrorTrap:
    MSGBOX "The following error occurred" & STR$(ERRCLEAR)
    RESUME ExitProgram
END FUNCTION

posted May 28, 2004 07:47 PM            

¿?

By the way, jazmin says thanx for all your replies!!!

Elias

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Last night i was decided to retreat, Then i decided not to.

posted May 28, 2004 10:44 PM            

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Last night i was decided to retreat, Then i decided not to.