# What is OPM

> The OPM language · https://spoletta.com/docs/opm

OPM, the Object-Process Methodology, is a modelling language standardised as ISO 19450. It describes any system, from a factory to a code review, with just two kinds of thing and a small set of links between them. Spoletta uses it as the language flows are drawn in.

## Two kinds of thing

*Diagram: An object exists, or can exist.*

*Diagram: A process transforms objects.*

-   **Objects** are things that exist: a ticket, a patch, a release, a person. An object can be in one of several **states**, such as `draft` or `approved`. On the board an object has square corners.
-   **Processes** are things that happen: they create objects, use them up, change them, or change their state. On the board a process is rounded.

That is the whole cast. Unlike flowcharts, which draw only the steps, or data models, which draw only the data, OPM puts both on the same diagram. A process means nothing without the objects it transforms, and an object only changes when a process acts on it.

## Links say how they meet

Things are joined by **links**, in two families:

-   **Procedural links** join a process and an object, and say what the process does to it: creates it, needs it, consumes it, changes it, or waits for it to enter a state. These drive a run. See [Procedural links](https://spoletta.com/docs/procedural-links.md).
-   **Structural links** join objects, and say what an object is made of or is a kind of. They give an object its shape. See [Structural links](https://spoletta.com/docs/structural-links.md).

## One model, two views

Every OPM diagram can also be read as sentences of OPL, the Object-Process Language. The two say exactly the same thing: the diagram for seeing the whole at a glance, the sentences for checking each fact.

OPL:

```text
Editor is a person.
Post can be good or weak.
Review is a human process, which a person carries out.
Editor handles Review.
Review yields Post as good or weak, deciding which.
```

## Managing size by zooming

Real processes have sub-steps. Rather than drawing everything on one huge diagram, OPM lets you **zoom into** a process: inside it is a diagram of its own. In Spoletta that is a flow process, and each level stays small enough to read. See [Zooming in](https://spoletta.com/docs/zooming.md).

## How Spoletta uses OPM

Spoletta keeps OPM's meaning and adds what a running system needs: each process has a *kind* saying who carries it out, each object holds JSON, a **start** node says where a run begins, and two plain connections between processes, *next* and *on failure*, cover ordering without data and exceptions. The pages that follow cover each construct in turn.

> **Note:** You don't need to know the ISO standard to use Spoletta. Everything you need is in this section, explained as the board draws it.