FILE: Fact Sheet on Jet 2.0/VB 3.0 Compatibility Layer (113683)


The information in this article applies to:

  • Microsoft Visual Basic Standard Edition for Windows 3.0
This article was previously published under Q113683

SUMMARY

This article gives the complete text contents (with corrections) of the fact sheet for the Microsoft Jet 2.0/Visual Basic 3.0 Compatibility Layer.

MORE INFORMATION

Background Information

Visual Basic version 3.0, released in May of 1993, includes support for the Microsoft Access version 1.1 database engine, also known as the Microsoft Jet Database Engine (Jet). The Jet database engine gives Visual Basic developers the ability to create and distribute royalty- free applications with Jet as the underlying database engine. Microsoft Access version 2.0 contains a new version (2.0) of the Jet database engine that Visual Basic version 3.0 cannot access.

To enable Visual Basic version 3.0 applications to use Jet 2.0 databases, Microsoft created the Microsoft Jet 2.0/Visual Basic 3.0 Compatibility Layer (Compatibility Layer). Use of the Compatibility Layer is optional-- Microsoft Access version 2.0 reads and writes Jet 1.1, so Visual Basic/Jet 1.1 applications do not need to be converted even if users upgrade to Microsoft Access version 2.0. There are some major benefits to upgrading, though, and these are described below.

What the Compatibility Layer Includes

The complete Compatibility Layer consists of the following pieces:
  • An updated version of the Visual Basic file that interfaces to Jet (VBDB300.DLL).
  • A new file (MSAJT112.DLL) that maps the VBDB300.DLL file and the Microsoft Jet 2.0 engine to each other.
  • A file that modifies the Visual Basic Crystal Report files to work with Jet 2.0.
  • Updated versions of the Jet-supported ISAM drivers (Paradox, FoxPro, and Btrieve).
  • A setup file that installs the layer and updates appropriate system files.
NOTE: Microsoft Access 2.0 must be installed on the destination computer or the Compatibility Layer won't install.

The setup file does not remove the Jet 1.1 files, but Visual Basic will be using the Jet 2.0 files, once setup is run. Visual Basic-based applications that use Jet 1.1 format databases will continue to operate because Jet 2.0 reads and writes Jet 1.1 format databases.

Visual Basic-based applications that create Jet 1.1 format databases can continue to do so through the Jet 2.0 files by changing a setting.

Benefits of Upgrading to Jet 2.0

Microsoft Access version 2.0, via Jet 2.0, provides a host of powerful new features that will be available in Visual Basic-based applications once the Compatibility Layer is installed:
  • Cascading updates and deletes allow users to delete or update a record and have all dependent records reflect the change.
  • Table-level validation provides greatly increased data integrity and security.
  • Rushmore query optimization greatly speeds execution of many common queries.
  • Virtually any view can be updated.
  • Support for the Paradox 4.x file format.
  • Support for the Btrieve 6.x file format.
  • Improved SQL Pass-through for non-standard SQL that needs to be sent to servers to execute, for example, stored procedures.
  • Improved SQL support such as UNION, Subqueries, and the new Top N query.

Limitations of Upgrading to Jet 2.0

The Compatibility Layer gives Visual Basic developers complete access to Jet 2.0 and all its new features, but there are a few limitations. These result primarily because the Visual Basic language has not changed and so the Visual Basic developer does not gain programmatic access to some of the new features. In many cases, Microsoft Access version 2.0 can be used to access features that are not directly available through Visual Basic:
  • Cascading updates and deletes are supported but must be specified using Microsoft Access version 2.0.
  • Table-level validation is supported but settings must be specified using Microsoft Access version 2.0.
  • Jet 2.0 now supports zero-length strings, so some updates may fail if validation rules require zero-length strings, which Visual Basic cannot use.
  • Jet 2.0 databases using any of the eight new language sort sequences will be read-only in Visual Basic.
  • Jet 1.0 format databases cannot be created by Jet 2.0 files.

Distribution Issues

After obtaining the first Compatibility Layer, Microsoft allows propagation of that layer free-of-charge to other eligible Visual Basic licensees within the same organization. Applications created with Visual Basic and the new Jet 2.0 database engine are, as before with Jet 1.1, fully distributable royalty-free to application end users.

How to Obtain the Compatibility Layer


To obtain the Compatibility Layer, choose one of the following methods:
  • The following file is available for download from the Microsoft Download Center:

    Comlyr.exe

    For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

    119591 How to Obtain Microsoft Support Files from Online Services

    Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.
  • If you are unable to access the source(s) listed above, you can have COMLYR.EXE mailed or faxed to you by calling Microsoft Technical Support Monday through Friday, 6:00 a.m. to 6:00 p.m. Pacific time at (425) 646-5105. If you are outside the United States, contact the Microsoft subsidiary for your area. To locate your subsidiary, go to the Microsoft Web site http://www.microsoft.com/worldwide
  • Purchase the Microsoft Access Developer's Toolkit (ADT) version 2.0 available through resellers or direct from Microsoft. The price is $495 for new users. However, until August 31, 1994, current Microsoft Access Distribution Kit version 1.1 and Visual Basic version 3.0 licensees will receive $100 off price via a rebate. All the files you need are included.
  • Purchase the Microsoft Office Developer's Kit (ODK) and Microsoft Access version 2.0. Both products are available through resellers or direct from Microsoft. The suggested retail price for the ODK is $99.95. If you own Visual Basic version 3.0 Professional Edition, you can get the ODK direct from Microsoft for $49.95.

    The ODK will also be available as a standard component in all new packages of Visual Basic version 3.0 Professional Edition. The ODK comes on CD-ROM only.

    The ODK includes all files in the Compatibility Layer except the main Microsoft Access version 2.0 database engine file, which is available in Microsoft Access version 2.0. Therefore to use the ODK edition of the Compatibility Layer, you need to purchase Microsoft Access version 2.0. The license in the ODK permits distribution of this file with Visual Basic version 3.0-based applications. Suggested retail price for Microsoft Access version 2.0 is $495. Until August 31, 1994, current Microsoft Access version 1.x users can upgrade for $99. And those users upgrading from competing products and from Microsoft Office can purchase Microsoft Access version 2.0 for $129.
Modification Type:MajorLast Reviewed:7/21/2005
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