Blog
Decompiler internals and field notes.
How the parsers, control-flow engine and rule extractor work, and what we learn reading legacy cores with the people who own them.
Building control-flow graphs for PERFORM THRU, GO TO and ALTER
COBOL has no functions, only paragraphs and ranges of paragraphs, and control can leave a range by any door it likes. A rule extractor that gets this wrong attributes rules to the wrong branch.
All posts
12 articles · written by PYD ENTERPRISES engineers and architects
- Modernization strategy1 Sept 2026What the 2020 unemployment insurance crisis teaches about legacy rulesCOBOL took the blame when state benefit systems buckled in April 2020. The real lesson is about how quickly anyone could find and change the rules.Sahil Saxena · 7 min read
- Engineering14 Jul 2026PL/SQL lineage: finding the side effects hidden in triggers and packagesStored procedures rarely do only what their names say. How PYD ENTERPRISES traces column-level lineage through triggers, package state and dynamic SQL.Pranav Kulkarni · 8 min read
- Modernization strategy9 Jun 2026Fixed-price discovery and the systems integrator margin problemWhy fixed-price modernization bids lose margin in discovery, worked arithmetic for a 2 million line program, and how a rule inventory changes the bid.Rohit Mehra · 7 min read
- Testing28 Apr 2026Behavioral equivalence testing: proving a new service matches the old oneHow PYD ENTERPRISES derives equivalence fixtures from branch predicates, compares decimal results exactly and reports coverage per extracted rule.Nandini Subramanian · 7 min read
- Engineering24 Mar 2026Synthesizing OpenAPI 3.1 from CICS COMMAREAsA CICS program's COMMAREA is an untyped request and response in one buffer. Here is how dataflow separates the two and maps PICTURE clauses to JSON Schema.Pranav Kulkarni · 8 min read
- Mainframe17 Feb 2026Extracting interest calculation rules from a COBOL loan servicing coreBackward slicing from an accrued interest field: day-count bases, non-accrual status, rounding placement and the tests that prove a rewrite matches.Venkatesh Iyer · 8 min read
- Security20 Jan 2026Running static analysis in an air gap: how PYD ENTERPRISES ships without phoning homeThe deployment architecture behind zero code egress: signed bundles, offline license keys, egress-deny network policies and what security teams verify first.Shalini Rao · 7 min read
- Engineering9 Dec 2025Why language models get COMP-3 arithmetic wrongPacked decimal, implied scale, truncation on MOVE and ROUNDED semantics: why a chat model reading COBOL text produces confident, wrong arithmetic.Pranav Kulkarni · 7 min read
- DMN & rules4 Nov 2025DMN 1.5 for mainframe rating engines: from EVALUATE to decision tablesHow procedural COBOL rating logic maps to DMN 1.5 decision tables, which hit policy to choose, and where the mapping needs a human decision.Venkatesh Iyer · 8 min read
- Engineering7 Oct 2025Resolving COBOL REDEFINES in the AST: byte offsets, aliases and discriminatorsHow the PYD ENTERPRISES COBOL front end turns REDEFINES overlays into a byte-accurate storage model, alias sets and typed JSON Schema variants.Nandini Subramanian · 8 min read
- Modernization strategy16 Sept 2025Why legacy modernization fails in discovery, not in codingMost modernization overruns are decided before a line of new code is written. Here is where discovery breaks and how to make it an engineering artifact.Sahil Saxena · 7 min read
Newsletter · monthly
The Modernization Architect
One deep dive a month on mainframe decompilation, DMN extraction and legacy migrations, written by the engineers who build the parsers. No product announcements dressed up as research.
Legacy anti-patterns catalog
25 legacy anti-patterns, mapped to modern designs.
From COBOL ALTER and GO TO DEPENDING ON to EJB entity beans and PL/SQL cursors: why each is dangerous during migration, how it is detected, and the before and after code.
Explore the catalogStop spending six months reading legacy code by hand.
Run PYD ENTERPRISES on 100,000 lines of COBOL or Java in your private VPC and review OpenAPI specs and DMN tables tomorrow.