Migration guide
Informix 4GL applications put validation in AFTER FIELD blocks, constraints in form files and data rules in embedded SQL. This guide shows how to gather all three into a specification for a Java rebuild.
By Pranav Kulkarni, Head of Language Engineering · Updated 15 Oct 2026
Technical syntax challenges
INPUT BY NAME ... AFTER FIELD cust_num ... NEXT FIELD cust_num validates one field at a time, often with a SELECT in the middle. Each AFTER FIELD block is a rule with a precondition (the cursor left the field), and the order of fields can matter when later checks use earlier values.
The .per form's ATTRIBUTES section sets REQUIRED, NOENTRY, UPSHIFT, INCLUDE = (0.01 TO 99999.99), FORMAT and DEFAULT per field. These are input constraints the program never repeats, so extraction must read the form alongside the 4GL source.
In 4GL, as in SQL, a comparison with NULL is not true, so IF r_ord.ship_date < TODAY does not fire when the date is NULL. Unless the form field is REQUIRED, a blank date passes the check. The spec has to state this explicitly.
WHENEVER ERROR CONTINUE turns SQL errors into a value in status or SQLCA.SQLCODE that the code may or may not test. NOTFOUND (100) is a business branch; other negative codes may be ignored entirely in that scope.
DEFINE r RECORD LIKE orders.* types variables from the database schema at compile time, so types live in the catalog. CONSTRUCT builds WHERE clauses from user query-by-example input, which becomes a search API with defined filter semantics.
Extraction workflow
The sequence a PYD ENTERPRISES Discovery Scan runs for this stack. Every output links back to source file and line range.
Ingest .4gl modules, .per form specifications, GLOBALS files, the makefiles that link programs and the Informix schema for tables referenced with LIKE.
PYD ENTERPRISES types every RECORD LIKE and LIKE column variable from the schema, including DECIMAL(p,s), MONEY, DATE and DATETIME qualifiers.
Form field attributes are linked to the program variables bound in INPUT BY NAME, INPUT ARRAY and DISPLAY ARRAY, so each field has its full constraint set.
BEFORE FIELD, AFTER FIELD, ON KEY and NEXT FIELD jumps are modeled as a state machine per screen, with SQL calls and status checks along each path.
Each validation becomes a rule with its message text, and calculations become DMN tables, all linked to 4GL and form line numbers.
Request schemas with merged constraints, OpenAPI 3.1 operations for each screen action and fixtures, including NULL and boundary cases, are exported.
Legacy in, specification out
Left: the Informix 4GL construct as it sits in production. Right: the reviewed artifact your Java engineers build against. PYD ENTERPRISES produces the spec and the tests; your team writes the service.
LEGACY SOURCE
1# ordent.per: order_amt = orders.order_amt, REQUIRED,2# INCLUDE = (0.01 TO 99999.99), FORMAT = "$$$,$$$.&&";3DEFINE r_ord RECORD LIKE orders.*4DEFINE l_hold CHAR(1)56INPUT BY NAME r_ord.cust_num, r_ord.ship_date, r_ord.order_amt7 AFTER FIELD cust_num8 SELECT credit_hold INTO l_hold FROM customer9 WHERE customer_num = r_ord.cust_num10 IF status = NOTFOUND THEN11 ERROR "Unknown customer"12 NEXT FIELD cust_num13 END IF14 IF l_hold = "Y" THEN15 ERROR "Customer on credit hold"16 NEXT FIELD cust_num17 END IF18 AFTER FIELD ship_date19 IF r_ord.ship_date < TODAY20 OR r_ord.ship_date > TODAY + 90 THEN21 ERROR "Ship date must be within 90 days"22 NEXT FIELD ship_date23 END IF24END INPUT
EXTRACTED ARTIFACT
1{2 "screen": "Order entry (ordent)",3 "source": ["ordent.4gl:3-24", "ordent.per:18-19"],4 "fields": {5 "custNum": { "type": "integer", "required": false },6 "shipDate": { "type": "string", "format": "date", "required": false },7 "orderAmt": { "type": "number", "minimum": 0.01, "maximum": 99999.99,8 "required": true, "scale": 2 }9 },10 "rules": [11 { "id": "ORD-V1", "when": "customer not found", "reject": "Unknown customer" },12 { "id": "ORD-V2", "when": "customer.credit_hold = 'Y'", "reject": "Customer on credit hold" },13 { "id": "ORD-V3", "when": "shipDate < today or shipDate > today + 90 days",14 "reject": "Ship date must be within 90 days" }15 ],16 "review": [17 "shipDate NULL: ORD-V3 does not fire; field is not REQUIRED in the form",18 "custNum NULL: SELECT returns NOTFOUND, ORD-V1 fires"19 ]20}
Architectural best practices
In depth
Informix 4GL systems are rarely the size of a mainframe estate, but they are dense: a single module can hold screen flow, validation, SQL and reporting for a whole business function. Many still run order entry, inventory or policy administration at mid-sized companies, maintained by a shrinking group of people who know the language. That makes extraction urgent and also tractable, because the forms and the schema give the analyzer strong type information.
PYD ENTERPRISES extracts the rules, contracts and fixtures and links each one to .4gl and .per lines. It does not convert 4GL into Java. Your Java team builds services and screens against the reviewed spec.
Three validations come out cleanly: unknown customer, credit hold and the 90-day ship window. The review items are where the value is. The ship date is not REQUIRED in the form, so a blank date passes ORD-V3 and the order is saved without one. Whether that is a feature (ship when ready) or a defect is a business question. The analyzer also notes that the credit hold check runs only when the cursor leaves the customer field; if the user never enters that field after a hold is placed in another session, the order still saves. A server-side API that validates the whole request removes that gap, and the spec makes the change visible.
FAQ
Informix 4GL source is parsed, including INFORMIX-4GL and the compatible syntax used by later 4GL compilers. Vendor-specific extensions are flagged if not recognized, rather than skipped.
Yes. Report functions are parsed; calculations and aggregates in them are extracted as rules, and layout logic is classified as presentation.
No. A schema export is enough to resolve LIKE declarations. A test database helps when running the generated fixtures against the existing programs.
Request a codebase scan and review extracted rules, contracts and fixtures for your own Informix 4GL estate, inside your VPC.