The jPOS Common Message Format specification is getting an update. CMF v3 is still a work in progress, but an early-access draft is available at jpos.org/doc/jPOS-CMFv3.pdf for anyone who wants to follow along. The most significant addition in v3 is first-class support for the ISO 8583 dataset model—and that's what this post is about.
Every ledger has a set of transactions it posts over and over. The accounts change, the amounts change, sometimes the counterparty changes—but the structure is always the same. A fee charge is always a debit to the customer account and a credit to fee income. A settlement is always the same four entries. A foreign exchange conversion follows the same arithmetic every time.
Freeform posting can handle all of these, but it puts the entire burden of correctness on the operator: right accounts, right sides, right layer, right formula—every time, by hand. Templates solve this. A template captures the invariant structure of a transaction and exposes only the parts that actually vary. Everything else is handled by the ledger.
Most ledger enforcement is hardcoded. If the business needs a new limit—a maximum account balance, a cap on transaction size, a rule that blocks weekend postings—someone files a ticket, a developer writes a check, the code ships in the next release. That cycle takes days or weeks, and the logic lives in application code rather than in the ledger where it belongs.
MGL solves this with Dynamic Rules. A dynamic rule is a CEL expression that the system evaluates on every posting, in real time, before the transaction is committed. If the expression returns false, the transaction is denied. No code change required. No deployment.
Most accounting systems that want to show derived figures—variance against budget, percentage execution, a consolidated multi-currency total—end up solving the problem the same way: periodic batch jobs that write synthetic entries to hold the computed values, or reporting scripts that reconstruct the computation at query time outside the ledger.
Both approaches have the same flaw. The derived figures live in a different place than the authoritative entries. They get stale. They diverge. Reconciling them back to source is always someone's problem.
MGL solves this with virtual layers. A virtual layer carries a formula instead of entries. Its balance is computed on the fly from physical layers—always derived from the same source of truth, always accurate to the query date, with no batch job required.
Most log viewers are built around the assumption that logs are lines of text. Search is grep. Filtering is awk. Correlation is copy-pasting timestamps and hoping for the best. The infrastructure to make that tolerable — log shippers, ingestion pipelines, index clusters — adds cost and complexity, and the result is still a flat text interface.
jPOS' Log Viewer takes a different approach, and it can do so because jPOS's logging is different at the source.