00 · Gravity Migration

Don't move the mainframe. Use its mass.

Your mainframe is the only complete record of how your business really works. Gravity Migration turns that record into Gravity Standard specifications: cited, confirmed, tested and proven against what production actually does.

Start with the survey See the translations

A gravity assist uses a massive body's pull to gain speed without burning fuel. Decades of encoded behavior can do the same for a specification.

The position

Migrate the behavior, not the components.

Replacing each mainframe subsystem with an AWS service rebuilds 1987 on Lambda. Nightly sweeps stay nightly, and every odd workaround makes the trip with nobody having chosen to keep it.

Here, the estate is evidence. The deliverable is a set of Gravity Standard specifications that people have confirmed. The Standard then supplies the rest, as it does for any application.

The code can tell you what the system does. Only a person can tell you whether it should keep doing it.

Read this first

Not everything should move.

A boundary from the Standard

Gravity Standard is the front door and workflow layer, and it deliberately doesn't hold ledger-class data such as balances. Most of an estate's workflow can move onto it, and that's usually where the business feels trapped. The ledger can't.

So this method alone won't get most core systems off the mainframe. The machine stays on until its ledger has a home, which usually means a core banking or ledger product. Each capability gets a recorded fate: move, retain, replace or retire.

The translations

Every subsystem gives up something different.

Nothing here maps one-for-one. Each row shows what to extract, and a Tidewater example you can follow in its chapter.

Source	Extract as	Tidewater example	Classic trap	Chapter
COBOL, PL/I	Rules	Late fee in `ACLP210`	Truncating arithmetic	Rules
RPG, CL	Rules	Insurance lapse in `KTLAPSE`	A rule in a system being replaced	Rules
Java	Rules, API contracts	BankLink payoff quotes	Behavior in server config	Rules
Flat files, VSAM	Record types	`PMT-DUE-REC` to Scheduled Payment	REDEFINES, magic values	Data
Db2	Domains, statuses	`TWDB.LOAN` to Loan	Stored procedures, sort order	Data
Batch, JCL, CL	Purpose, deadline	The nightly late sweep	Rules in a sort card	Processes
True bulk jobs	Calendar, volume, failure rules	Monthly Statements from `TWSTMT`	Looks like bulk extraction to KMS	Processes
IBM MQ	Who talks to whom, and why	Funding notices, loan status	Order, full records, unwatched queues	Processes
Postings to a retained system	Direct and indirect rules	Post Late Fee to Anchor Core	Posting twice after a timeout	Processes
Existing records	What converts, exceptions	Convert Scheduled Payments	Loading records that start real work	Data
Partner system access	Actors, providers, tenant roles	The clearing service across banks	Standing access to every bank	Access
Partner files	Partners, formats	Remittances from Pinecrest	Silent repairs	Processes
RACF, object authority	Actors, access rules	`LATEOPS`, `*PUBLIC`, `TWWEB`	Stale grants, no bank boundary	Access
CICS, 3270, 5250	Tasks, commit boundaries	`TWPY` to Payment Correction	Losing keyboard speed	Screens
Web interfaces	Tasks, UI-only rules	BankLink's second approver	A rule only the browser knew	Screens
Reports, print	Who acts on what	`TWRPT44`, `TWRPT09`	Reports nobody reads	Survey
Code tables, utilities	Choices, parameters	`TWCODES` grace days	Meaning in a shared table	Survey
Archives, audit	Retention obligations	Late-fee tape generations	Tapes nobody can read later	Cutover

The chapters

Read in order, or jump to what you're holding.

Survey

What you have, what's alive, and each capability's fate.

Evidence

Artifacts become cited claims that a person confirms.

Data

Copybooks and tables become typed, classified record types.

Rules

Procedural code becomes numbered, testable outcomes.

Processes

Batch, messages and files become small state machines.

Access

Decades of grants become actors, skills and reasons.

Screens

Terminal maps become tasks, without losing the keyboard.

Proof

Parallel runs, and a named decision on every difference.

Cutover

Small slices, one writer, a rehearsed way back.

The worked example

Tidewater, before the Standard.

Every example follows Tidewater, the fictional lender from Gravity Standard. It adds the history behind that company: Anchor Core's nightly jobs, the portal partner banks use, and an IBM i inherited in an acquisition. All of it is invented.

Read the full estate catalog, which is also written for AI assistants.

System	Platform	Fate
Anchor Core ledger	z/OS, Db2, COBOL	Retain
Anchor Core workflow	Batch, CICS, MQ	Move
BankLink	Java on WebSphere	Move
KeelTrack	IBM i, RPG, 5250	Replace

Draft 0.1. Gravity Migration is an independent method, not affiliated with IBM or AWS. IBM Z, z/OS, IBM i, CICS, Db2, RACF, IBM MQ and WebSphere are trademarks of IBM. AWS service names are trademarks of Amazon.