All About MEL

                   The use of MEL (Migration Export Library)
                      in estimating porting effort to OS/2.


                              By Mark Bosakowski


Abstract

A new set of extensions to the base OS/2 Warp toolkit called the DAPIE API
library has been developed by IBM to assist software developers when porting
software from Microsoft Windows to OS/2 Warp.  DAPIE (Developer API Extensions)
is an OS/2 Warp library that provides direct emulation of over 800 Windows
API's and can greatly reduce the overall porting effort.


To compliment DAPIE, a library named MEL (Migration Export Library) has been
developed that will help the Windows developer in the analysis stage of the
porting process.  MEL will help decide if a DAPIE based porting strategy is
appropriate by isolating the Windows API's that are not supported by DAPIE in
their codebase.  MEL accomplishes this task in the Windows development
environment, thus providing a quick and accurate breakdown of the DAPIE and
non-DAPIE API's in the application.


The information generated by MEL provides the raw data required to accurately
estimate the size and scope of porting DAPIE and non-DAPIE Windows code to OS/2
Warp.



The MEL Library

MEL is a Windows library whose sole purpose is to help the Windows developer
determine how much of their codebase will not be supported in a porting effort
when using the DAPIE library.   MEL would not be used in an actual porting
effort or in the OS/2 development or runtime environment.   The primary use
of MEL is as a tool to quickly identify the Windows API's that would not be
supported in a DAPIE based porting strategy.  Because MEL works in the Windows
environment, there is no need to install OS/2, or the OS/2 development tools.


How MEL Works

In layman's terms, the MEL library is a facade.  In a Windows development
environment, MEL looks, compiles and links like the Windows libraries.
Because the MEL library only includes the DAPIE supported Windows API's,  a
program compiled and linked with MEL will never link or run.  However, an
artifact of the linking process,  a list of unresolved Windows API's will be
generated by the linker.   The list of unresolved Windows API's is by
definition the "non-DAPIE" API set.



Using MEL to Determine a Porting Strategy

MEL is only useful in the first stage of the software porting process, which
is to determine the best porting strategy to pursue.  DAPIE is a new and unique
strategy for porting to OS/2 Warp, and one that is best suited for applications
that have a high percentage of Windows API's that are directly supported in
the DAPIE library .  To determine if  DAPIE is an appropriate porting strategy,
the developer needs to know how much of their codebase will be supported by
the DAPIE library in the OS/2 Warp environment.


                                 All About MEL



The DAPIE decision process is outlined below.

	- Compile and link Windows source code with the MEL library
          and header files.
	- Organize the list of Windows API's that were not resolved
          by the linker.
	- Sort the list by the frequency of calls to each API.
	
With further analysis of this list (The Windows non-DAPIE  API's), one can
determine if the remaining porting effort will be easy, difficult or in some
cases, impossible.

This list of API's can then be used with other porting tools, such as the
analysis reporting tool in the SMART Toolset, to determine the porting effort
required.


Where can I Obtain MEL?

MEL is available on the internet World Wide Web Home page
www://os2.migration.ibm.com, or can be obtained from the Migration
Assitance Team at (407) 443-7700.