Working with DBISAM Using Microsoft .NET
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by Bhuban Mohan Mishra
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About DBISAM

DBISAM is an embedded database engine which is available for programming languages that can use ODBC for data access.  DBISAM can be used as a single-user, multi-user or client-server engine.

General Architecture

DBISAM is session based where each session is equivalent to a virtual user.  In a given application there can be many active sessions.  The sessions are of 2 types.

·         Local Session: A local session can directly access the database tables via Windows or Linux APIs to the local storage medium.

·         Remote Session: A remote session uses sockets to communicate to a database server over a network using TCP/IP protocol.

The main drawback of DBISAM is that it does not support Referential Integrity.

Databases

DBISAM uses the physical directories in Operating System’s file system to represent databases. The tables in DBISAM are represented by three physical files in the database.

·         .dat (Data Files) which are the actual tables in the Database that store records.

·         .idx (Index Files) which store index definitions and pages.

·         .blb (BLOB Files) that store BLOB blocks related to tables.

Data Types

The data types used in DBISAM are also supported by other databases or relational databases, but with some exceptions.  A comparison between the data types of DBISAM and SQL Server is given below.

Listing 1

Data Type

Description

SQL Server Equivalent

String

Fixed length fields that can store up to 512 characters. The trailing blank spaces are automatically trimmed from any strings entered into string fields.

VARCHAR

FixedChar

Same as string fields with the exception that trailing blank spaces are not automatically removed from any strings entered into them.

CHAR or

CHARACTER

GUID

Same as string fields with the exception that they are fixed at 38 bytes in length and are always used to store the string representation of a GUID value.

UNIQUEIDENTIFIER

Bytes

Fixed in length and can store up to 512 bytes in a single field.

BYTES

Blob

Variable in length and may contain up to 2 gigabytes of data.

NTEXT or IMAGE

Memo

Variable in length and may contain up to 2 gigabytes of data minus a NULL terminator.

TEXT or LONGVARCHAR

Graphic

Variable in length and may contain up to 2 gigabytes of data.

IMAGE

Date

Date fields contain dates only.

DATETIME

Time

Time fields contain times only.

DATETIME

TimeStamp

Contain both a date and a time.

TIMESTAMP

Boolean

Contain logical True/False values.

BIT

SmallInt

Contain 16-bit, signed integers.

SMALLINT

Word

Contain 16-bit, unsigned integers.

 

Integer

Contain 32-bit, signed integers.

INTEGER or INT

AutoInc

Contain 32-bit, signed integers.

INT with Identity

LargeInt

Contain 64-bit, signed integers.

BIGINT

Float

Contain 64-bit floating-point numbers (doubles).

FLOAT

Currency

Currency fields are the same as Float fields.

MONEY

BCD

BCD fields contain a 34-byte TBcd type.

NUMERIC


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User Comments

Title: Re: new extension db4   
Name: Bhuban M Mishra
Date: 2008-03-24 11:56:12 AM
Comment:
Hi Nicola,

I went through the Eleviate Software site, but I did not found the details about .db4 files. Might be they have not updated the details of the new version.

According to the following link,
http://www.elevatesoft.com/manual?action=mantopic&id=dbisam4&product=b&version=2005&category=1&topic=1

It says that the files still have .dat extension. I do not have access to the latest DB. I think, the way .dat files are accessed, the .db4 files can also be accessed in the same manner.

If possible, you can search for the updated drivers if available for the db4 files.

Thanks,
Bhuban
Title: new extension db4   
Name: Nicola
Date: 2008-03-14 6:21:54 AM
Comment:
Hallo! i have new version dbisam with new versione.. extension file data is .db4 and not .dat... can u help me?? with new versione.. i want use this code..
thank u soo much
nicola
Title: GOOD ARTICLE   
Name: ADAM
Date: 2007-07-16 12:29:55 PM
Comment:
I looked for a few hours about information about some unkown database file types I had and didnt find anything until I found this article. This article and the help it provided is greatly appreciated. Thanks.
Title: Re: Where do I find DBISAM ODBC Driver?   
Name: Bhuban
Date: 2006-11-03 9:00:08 PM
Comment:
The ODBC Driver provided by Elevate Software is the only driver available as per my knowledge. I have also used the same. As per your problem is concerned, each table that has BLOB fields must have a .blb file which remains in the same folder as the table. Though I have not worked with BLOBs, there are certain DBISAM viewers available that shows the structure and data in the tables. You can use one of them to check whether the data in the BLOB field is intact.
Title: Where do I find DBISAM ODBC Driver?   
Name: TLR
Date: 2006-11-03 10:30:48 AM
Comment:
I have found one ODBC Driver from Elevate Software, but it seems to choke whenever I try a select that includes a BLOB column. Can you recommend some other ODBC Driver?
Title: Very Informative Article   
Name: Prasanjit Ahuja
Date: 2006-10-06 5:23:33 AM
Comment:
Very Informative article. Keep it up.
Title: Panda   
Name: Supriti
Date: 2006-10-05 11:10:09 AM
Comment:
Hi,
Thanks for the information about a new database.This may be helpful for me in future.
Title: Working with DBISAM Using Microsoft .NET   
Name: Himanshu Sahoo
Date: 2006-10-03 6:18:10 AM
Comment:
Nice Article.Well done.






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