After talking about some experience with legacy modernization (or migration), I received information from Blue Phoenix about their approach to modernization.
Before talking about modernization, it's important to think about the following issue from two points of view.
From a user viewpoint, "paving the cowpaths" means that the legacy usability issues have now been modernized without being fixed. The issues remain. A dumb business process is now implemented in a modern programming language. It's still a dumb business process. The modernization was strictly technical with no user-focused "value-add".
From a technical viewpoint, "paving the cowpaths" means that bad legacy design, bad legacy implementation and legacy platform quirks have now been modernized. A poorly-designed application in a legacy language has been modernized into a poorly-designed application in yet another language. Because of language differences, it may go from poorly-designed to really-poorly-designed.
The real underlying issue is how to avoid low-value modernization. How to avoid merely converting bad design and bad UX from one language to another.
Consider that it's possible to actually reduce the value of a legacy application through poorly-planned modernization. Converting quirks and bad design from one language to another will not magically make a legacy application "better". Converting quirky code to Java will merely canonize the quirks, obscuring the essential business value that was also encoded in the quirky legacy code.
Focus on Value
The fundamental modernization question is "Where's the Value?" Or, more specifically, "What part of this legacy is worth preserving?"
In some cases, it's not even completely clear what the legacy software really is. Old COBOL mainframe systems may contain hundreds (or thousands) of application programs, each of which does some very small thing.
While "Focus on Value" is essential, it's not clear how one achieves this. Here's a process I've used.
Step 1. Create a code and data inventory.
This is essential for determine what parts of the legacy system have value. Blue Phoenix has "Legacy Indexing" for determine the current state of the application portfolio. Bravo. This is important.
I've done this analysis with Python. It's not difficult. Many organizations can provide a ZIP file with all of the legacy source and and all of the legacy JCL (Z/OS shell scripts). A few days of scanning can produce inventory summaries showing programs, files, inputs and outputs.
A suite of tools would probably be simpler than writing a JCL parser in Python
A large commercial operation will have all kinds of source checked into the repository. Some will be inexplicable. Some will have never been used. In some cases, there will be executable code that was not actually built from the source in the master source repository.
A recreational project (like HamCalc) reveals the same patterns of confusion as large multi-million dollar efforts. There are mystery programs which are probably never used; the code is available, but they don't appear in shell scripts or interactive menus. There are programs which have clear bugs and (apparently) never worked. There are programs with quirks; programs that work because of an undocumented "feature" of the language or platform.
Step 2. Capture the Data.
In most cases, the data is central: the legacy files or databases need to be preserved. The application code is often secondary. In most cases, the application code is almost worthless, and only the data matters. The application programs serve only as a definition of how to interpret and decode the data.
Blue Phoenix has Transition Bridge Services. Bravo. You'll be moving data from legacy to new (and the reverse, also.) We'll return to this "Build Bridges" below.
Regarding the data vs. application programming distinction, I need to repeat my observation: Legacy Code Is Largely Worthless. Some folks are married to legacy application code. The legacy code does stuff to the legacy files. It must be important, right?
"That's simple logic, you idiot," they say to me. "It's only logical that we need to preserve all the code to process all the data."
That's actually false. It's not simple logic. It's just wishful thinking.
When you actually read legacy code, you find that a significant fraction (something like 30%) is trivial recapitulation of SQL's "set" operations: SQL DML statements have an implied loop that operates on a set of data. Large amounts of legacy code merely recapitulates the implied loop. This is trivially true of legacy SQL applications with embedded SQL; explicit FETCH loops are very wordy. There's no sense in preserving this overhead if it can be avoided.
Programs which work with flat files always have long stretches of code that models SQL loops or Map-Reduce loops. There's no value in the loop management parts of these programs.
Another significant fraction is "utility" code that is not application-specific in any way. It's an application program that merely does a "CREATE TABLE XYZ(...) AS SELECT ....": a single line of SQL. There's no sense in preserving this through an "automated" tool, since it doesn't really do anything of value.
Also. The legacy code has usability issues. It doesn't precisely fit the business use cases. (Indeed, it probably hasn't fit the business use cases for decades.) Some parts of the legacy code base are more liability than asset and should be discarded in order to simplify, streamline or improve operations.
The high value processing.
Step 3. Extract the Business Rules.
Once we've disposed of overheads, utility code, quirks, bad design, and wrong use cases, what's left are a the real brass tacks. A few lines of code here and there will decode a one-character flag or indicator and determine the processing. This code is of value.
Note that this code will be disappointingly small compared to the total inventory. It will often be widely scattered. Bad copy-and-paste programming will lead to exact copies as well as near-miss copies. It may be opaque.
IF FLAG-2 IS "B" THEN MOVE "R" TO FLAG-BC.
Seriously. What does this mean? This may turn out to be the secret behind paying bonus commissions to highly-valued sales associates. If this isn't preserved, the good folks will all quit en masse.
This is the "Business Rules" layer of a modern application design. These are the nuggets of high-value coding that we need to preserve.
These are things that must be redesigned when moving from the old database (or flat files) to the new database. These one character flag fields should not simply be preserved as a single character. They need to be understood.
The business rules should never be subject to automated translation. These bits of business-specific processing must always be reviewed by the users (or business owners) to be absolutely sure that it's (a) relevant and (b) has a complete suite of unit test cases.
The unique processing rules need to have modern, formal documentation. Minimally, the documentation must be in the form of unit test cases; English as a backup can be helpful.
Step 4. Build Bridges.
A modernization project is not a once-and-done operation.
I've been told that the IT department goal is to pick a long weekend, preferably a federal Monday holiday weekend (Labor Day is always popular), and do a massive one-time-only conversion on that weekend.
This is a terrible plan. It is doomed to failure.
A better plan is a phased coexistence. If a vendor (like Blue Phoenix) offers bridge services, then it's smarter and less risky to convert back and forth between legacy and new over and over again.
The policy is to convert early and convert often.
A good plan is the following.
- Modernize some set of features in the legacy quagmire of code. This should be a simple rewrite from scratch using the legacy code as a specification and the legacy files (or database) as an interface.
- Run in parallel to be sure the modern version works. Do frequent data conversions from old to new as part of this parallel test.
- At some point, simply stop converting from old to new and start using the new because it passes all the tests. Often, the new will have additional features or remove old bugs, so the users will be clamoring for it.
The unconverted code is a net cost savings.
Automated translation will tend to pave all the cowpaths: good, bad and indifferent. Once the good features are located, a manual rewrite is just as efficient as automated translation.
Automated translation cannot capture meaning, identify use cases or write unit test cases. Thoughtful manual analysis of meaning, usability and unit tests is how the value of legacy code and data is preserved.