> For the complete documentation index, see [llms.txt](https://host2host.onibonje.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://host2host.onibonje.com/docs/24-transformation-and-messaging.md).

# Transformation and Messaging Standards

## 1. Overview

**Modules:** `h2h-transform-core`, `h2h-transform-iso20022`, `h2h-transform-mt940`

Transforms map external formats ↔ [canonical model](/docs/29-canonical-data-model.md). Specifications stored in `transform_spec` — not in code.

***

## 2. Supported Standards

| Standard               | Direction        | Module                | Message types            |
| ---------------------- | ---------------- | --------------------- | ------------------------ |
| **CSV**                | Inbound/Outbound | transform-core        | Bulk payments, ACK       |
| **Fixed-width**        | Inbound          | transform-core        | Legacy corporates        |
| **JSON**               | API              | transform-core        | REST payloads            |
| **XML**                | Inbound/Outbound | transform-core + XSLT | Custom corporate         |
| **ISO 20022 pain.001** | Inbound          | iso20022              | Customer credit transfer |
| **ISO 20022 pacs.008** | Inbound          | iso20022              | FI credit transfer       |
| **ISO 20022 camt.053** | Outbound         | iso20022              | Account statement        |
| **ISO 20022 pain.002** | Outbound         | iso20022              | Payment status           |
| **SWIFT MT940**        | Outbound         | mt940                 | End-of-day statement     |
| **SWIFT MT942**        | Outbound         | mt940                 | Interim statement        |

***

## 3. Transform Pipeline

```mermaid
flowchart LR
  IN[Inbound format] --> ENG[Engine JOLT JSONata XSLT]
  ENG --> CAN[Canonical model]
  CAN --> ENG2[Engine]
  ENG2 --> OUT[Finacle or ACK format]
```

| Engine      | Best for                  |
| ----------- | ------------------------- |
| **JOLT**    | JSON/CSV → JSON canonical |
| **JSONata** | Expressions, API payloads |
| **XSLT**    | ISO 20022 XML, MT940      |

***

## 4. ISO 20022 Mapping (pain.001 → Canonical)

| ISO element                       | Canonical field           |
| --------------------------------- | ------------------------- |
| `GrpHdr.MsgId`                    | batchId (or mapped)       |
| `GrpHdr.NbOfTxs`                  | totalCount                |
| `GrpHdr.CtrlSum`                  | totalAmount               |
| `PmtInf.CdtTrfTxInf.Amt.InstdAmt` | instruction.amount        |
| `CdtrAcct.Id.IBAN`                | instruction.creditAccount |
| `DbtrAcct.Id.IBAN`                | instruction.debitAccount  |
| `RmtInf.Ustrd`                    | instruction.narrative     |

Specs in `transform_spec.spec_body` (JOLT chain).

***

## 5. MT940 Generation (Canonical → MT940)

| MT940 tag | Source                          |
| --------- | ------------------------------- |
| `:20:`    | batch/statement reference       |
| `:25:`    | account number                  |
| `:28C:`   | statement sequence              |
| `:60F:`   | opening balance                 |
| `:61:`    | transaction lines from postings |
| `:62F:`   | closing balance                 |

Module: `h2h-transform-mt940`

***

## 6. Validation Before Transform

1. File structure / XSD (ISO XML)
2. `validation_rule` on canonical (post-transform)
3. Business rules / scripts

Order: structural → transform → business validate.

***

## 7. ACK Transform (Canonical → Partner CSV)

Partner-specific ACK via `ack_template` + `transform_spec` targeting outbound CSV/XML.

***

## 8. Extensibility

| Need                     | Approach                                      |
| ------------------------ | --------------------------------------------- |
| New corporate CSV layout | New `transform_spec` in admin                 |
| New ISO message type     | `TransformEngineProvider` plugin or XSLT spec |
| Country variant          | Country-scoped transform in country pack      |

***

## 9. Related Documents

* [29 Canonical Data Model](/docs/29-canonical-data-model.md)
* [25 ACK/NACK Framework](/docs/25-ack-nack-framework.md)
* [04 Database-Driven Configuration](/docs/04-database-driven-configuration.md)


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