What is your Used rmcobol compiler? In Netexpress 5.x the rm syntax is integrated and I remember to have migrate a big project greater then yours to netexpress. Also visual cobol is able to do this! are the files index-sequential? There must be a reflection if it is no better to move to sql database?
Give us more information, a cobol source program as example and a data files! Are there text-oriented screens or windows screen? Are the printings text-oriented or graphical printings? What do you want in future?
You must share more information so that we are able to help you more!

If you have .COB files and .DAT files, then you do not appear to have any COBOL source files.  The .COB files are the (interpretive) object files.

RM/COBOL compiles .CBL source files to .COB (object) files.  The runcobol program uses the .COB files to run the applications.  RM/COBOL uses uses a compile-once, run anywhere, interpretive model much like Java.

The names of the .COB files might give a hint about whether your ERP system is a well known ERP system implemented in RM/COBOL (such as MCBA) or a 'home grown' bespoke system.

Programming is easy, commercial processes are simple, compilers are easy to use, doing it yourself without in-depth knowledge is a big risk that can only fail, but 100% of the winners took their chance! Good luck!

We are planning on using Codewatch. I will look into Netexpress. Had not heard of that one. I believe the files are index-sequential. Having reviewed the paths to SQL I plan on using Relativity for data access by other tools like Excel.

All the SQL tools seemed to be expensive and slower than the native files. I could use Relativity to scrape the data into our MS-SQL server if needed. I plan to review if updating the file formats to version 4 to reduce the chance we get shut down by a corrupted data file makes sense.

It makes extensive use of the SCREENS functions that are part of the RM/COBOL dialect. It is my understanding that SCREENS is part of RM/COBOL that is a rewrite to get into Visual COBOL.

I have all the source files. Many versions of them in fact. I think I have every version of every source file going back all 35 years. The system started out as a program called Telemerchant, but at this point more than half the code is bespoke.

My focus at this point is more maintain than rewrite. If I stumble onto the right programmer I might feel differently. I am glad to see replies here in this forum. Makes me feel less like I am standing at the bottom of a well.

My suggestion is if the applications are running weel and with no errors, why don't modernize the application with newer RM tools, like wow extension, relativity, instant SQL. Each of them can help you to expose the application to a modern environment and open all Data to others third tools like ODBC tools, excel, etc.

I plan on using Relativity. I don't know what the wow extension thing is. Instant SQL seems redundant with Relativity.

The only thing common to Relativity and InstantSQL is the use of ODBC.

Relativity provides ODBC access to data stored in native COBOL files.  No change to the COBOL application is required to allow this access.  

InstantSQL allows COBOL programs access to relational databases that provide an ODBC interface. The data are stored in whatever format is used by the specific database.   One must add/modify the COBOL application to add logic to connect to the database, and SQL queries to manipulate the data.

Relativity is a separately licensed product.  InstantSQL is distributed with the RM/COBOL development system.

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Cobol WOW  Extensions is a tool for development GUI applications basically with standard windows controls and where you can also expand the toolbox by adding ActiveX controls. These ActiveX controls can then be added to your windows and used by your programs. This capability provides an outstanding opportunity to add GUI features to your user interface. This visual approach makes building interactive applications and easily integrating your program logic with Windows GUI.

As Tom says, Relativity and InstantSQL are two different ways to get into SQL world. Relativity allows access to your Indexed Files through ODBC tools and InstantSQL allows you to access almost any SQL Data Base from you Cobol programs.