Compare approaches
PYD ENTERPRISES vs. generic LLM code migration
General-purpose language models explain a single program well and write plausible target code. They do not resolve copybooks across a library, compute storage layouts or follow control flow across hundreds of programs, and their output carries no proof of where a rule came from.
THE SHORT VERSION
Use language models to describe rules, not to find them. PYD ENTERPRISES' deterministic engine finds and locates every rule; a model you host can optionally name and summarize what the engine already proved.
Side by side
Generic LLM migration vs. PYD ENTERPRISES
| Dimension | Generic LLM migration | PYD ENTERPRISES |
|---|---|---|
| How it reads code | Predicts text from whatever fits in the context window | Parses every program into an AST and resolves every symbol |
| Cross-program scope | Limited to the files you paste or retrieve | One symbol graph across COBOL, JCL, CICS, DB2 and Java |
| COMP-3 and REDEFINES | Describes them; does not compute offsets | Byte-accurate layouts for every 01 level |
| Repeatability | Same prompt can produce different answers | Same source produces the same output, every run |
| Traceability | Citations are generated text and can be wrong | Each rule carries file and line range from the parser |
| Data handling | Often a hosted API; check your vendor terms | Runs air-gapped in your VPC; zero code egress |
| Strength | Explaining code, drafting prose and target code | Enumeration, lineage, specs and equivalence tests |
Why fluent is not the same as correct
Ask a chat model what a COBOL paragraph does and you will usually get a clear, confident answer. The trouble is in what it cannot see. A paragraph that moves a value into WS-RATE may be reading a field that another program wrote through a REDEFINES alias. A condition on ACCT-PREMIUM may be an 88-level name that tests three values of a status byte defined in a copybook three levels deep. An EXEC CICS LINK passes a COMMAREA whose layout lives in a different library. None of that is in the snippet, so the model fills the gap with something plausible.
Packed decimal is a good test. A field declared PIC S9(7)V99 COMP-3 occupies five bytes, holds nine digits with an implied decimal point, and keeps the sign in the low nibble of the last byte. Arithmetic on it follows COBOL truncation rules unless ROUNDED is specified. A model that translates it to a floating point type, or that ignores the truncation, produces code that passes casual review and fails reconciliation.
How PYD ENTERPRISES uses models, if you want it to
PYD ENTERPRISES' pipeline is deterministic up to the rule inventory: lexing, parsing, copybook expansion, symbol resolution, control-flow and data-flow graphs, program slicing and rule classification all run without a language model. That is what makes the output repeatable and auditable.
If you enable it, a language model that you host inside your own environment can propose human-readable names and one-paragraph descriptions for rules the engine has already located. The model never decides what code does, never adds or removes a rule, and its suggestions appear in the review view as editable text. Many regulated customers leave it off entirely.
Where generic models do help a modernization program
Language models are good at work around the specification: drafting target code from a reviewed DMN table and OpenAPI contract, writing documentation for the new service, explaining an unfamiliar construct to a developer who has never seen JCL. Feeding them PYD ENTERPRISES' exports instead of raw legacy source gives them a smaller, structured and verified context, which is a better input for any generator.
Fair is fair
When generic llm migration is the right call.
We would rather lose a deal than sell PYD ENTERPRISES where it does not fit.
- You need a quick explanation of one program or a handful of paragraphs, not a specification of a system.
- You are drafting target code from an already reviewed specification and will test it against equivalence fixtures.
- The code is small, self-contained and has no copybook, CICS or database dependencies worth resolving.
- Your security policy allows the code to be sent to the model, and a human will verify every statement it makes.
FAQ
Common questions.
Does PYD ENTERPRISES send our code to a language model?
No. The core engine uses no language model. The optional rule naming step runs only with a model you host inside your own environment, and it is off by default.
Can we use PYD ENTERPRISES output with our own coding assistant?
Yes. DMN tables, OpenAPI 3.1 contracts and JSON Schemas are open standards and make a far better prompt context than raw COBOL, because they are complete and already verified.
Is a large context window enough to fix the problem?
It helps with recall but not with resolution. A context window holds text; it does not compute storage offsets, expand copybooks in the right order or prove that a paragraph is unreachable.
Other comparisons
- PYD ENTERPRISES vs. manual code auditUse people for judgment and tools for enumeration.
- PYD ENTERPRISES vs. automated transpilersTranspilation moves the code; specification extraction moves the knowledge.
- PYD ENTERPRISES vs. rewrite from scratchRewrite the system, not the knowledge.
- PYD ENTERPRISES vs. lift-and-shift rehostingRehosting changes where the code runs; it does not change what you know about it.
Compare on your own code.
Run PYD ENTERPRISES on up to 100,000 lines for 14 days in your VPC and put the output next to whatever you use today.