Case Study: Migrating a VB6 Large Application to .NET

An IT services provider company has migrated an ERP application totaling 950,000 lines of VB6 code to .NET in 9 months.

There are 5 basic options dealing with a legacy VB6 application:

• Leave it as it is – if the application is rarely updated or changed
• Replace – if there is a similar commercial or open source application or service
• Migrate to .NET – using a migration tool which converts all VB6 code into equivalent .NET code
• Extend with .NET – add new functionality using .NET. .NET forms and controls can be added to a VB6 application with the help of Interop Form Toolkit 2.0 (PDF).
• Rewrite – hand writing the entire code in .NET. This is a viable approach when the initial VB6 application was poorly written and a re-write is desired, the application needs a major change to satisfy new needs, or the source code is not available.

If migration is the path to go, the next three solutions are helpful with that:

• Microsoft Visual Basic Upgrade Wizard. It is included in VS 2008 and works well with small and medium projects. For large, enterprise applications, the next two solutions are recommended by Microsoft.
• Visual Basic Upgrade Companion by ArtinSoft
• Visual Basic Migration Partner by Code Architects

Microsoft recently published a case study highlighting the success of the migration of 950,000 lines of VB6 code to .NET. The process was conducted by SiS, an Austrian IT company, using VB Migration Partner from Code Architects over a period of 9 months. The project was an ERP system built over 10 years and consisting of 33 applications. The best solution for this application was to migrate it rather than use a customized ERP application or rewrite it. Customizing a commercial ERP was not accepted because it would have cost 3-5 million Euros, it would take 2 years and no vendor guaranteed the implementation of all original features.

SiS selected 25,000 lines of code and tried to migrate them with various tools. VB Migration Partner was the best, the chunk of code being migrated, compiled and ready to run in 2.5 hours. They also reported that VB Migration Partner required the least amount of manual intervention to make the UI look like the original one.

The entire ERP application was migrated in 9 months by 3 developers totaling “3,650 developer-hours to migrate the code, 3,400 hours for code review and refactoring, and 1,300 hours for testing.” The code review was requested because the code would need further development in the future and none of the original developers were available. Total cost: 750,000 Euros, much less than the required one for a customized ERP. The process evolved in phases: when a module was done, it would be integrated with the rest of the VB application until the entire application would have been migrated to .NET.

Companies with major investments in VB6 can still make good use of their legacy assets by migrating them to .NET. Microsoft and its partners seem to have the tools for the job.

Related Topics:

• Development
• Architecture & Design
• Culture & Methods
• Stories & Case Studies
• .NET
• Change
• migration
• Visual Basic.NET
• VB 6

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