# Software Connector Classification

**In short:** Connector classification compares integration styles on shared questions, such as synchronous or asynchronous and one-to-one or one-to-many. The answers show how each style behaves when a side is down or an interface changes.

## Explanation

Integration styles are ways to let separate applications work together. Comparing them on the same questions makes the differences easier to see. This article covers the questions that the verified facts support.

**Synchronous or asynchronous.** In a synchronous call, the caller waits while the callee works. Remote procedure calls (see Remote Procedure Call) follow this pattern. They pass data and also hand over control, because the caller waits for the callee. In asynchronous exchange, the sender does not wait for the receiver.

**Direct or indirect.** File transfer is an indirect style. Each application writes files of shared data and reads files that others wrote. The exchange is asynchronous. Shared database is another style where applications share through a middle point: they store the data they want to share in a common database. See File Transfer and Shared Database.

**Cardinality.** This means how many parties take part. Messaging can broadcast one message to several receivers. That is a one-to-many connection.

**Reliability.** A synchronous call assumes the callee is available when called. If side B is down, the call has a problem. With asynchronous messaging, both systems do not need to be up at the same time. See Messaging.

**Adaptation.** Messaging can transform messages in transit. Neither sender nor receiver knows this happens. This helps when the two sides use different interfaces.

Use these questions as a checklist. Ask the same ones of every candidate style.

## Example

A shop system must tell a billing system about new orders. With a synchronous call, the shop waits for billing to answer. If billing is down, the order step is stuck. With asynchronous messaging, the shop sends the message and moves on. Billing reads it when it is back. Later, a reporting system can receive a copy of the same message, because one message can reach several receivers.

## Trade-offs

Synchronous calls are the usual way programs work, and they are simple to reason about. The price is that the callee must be available at that moment. Asynchronous messaging removes that need and allows in-transit changes and broadcast. The facts here do not compare the effort or cost of each style, so judge that for your own case.



## Checks

- For each integration, the document states whether the exchange is synchronous or asynchronous.
- For each synchronous call, the document says what happens when the callee is unavailable.
- Where one message must reach several receivers, the document names this one-to-many link.
- Where interfaces differ between systems, the document says where messages are transformed.

## Related

- [Software Connector](https://arc.fuet.ch/concepts/fundamentals/software-connector.md)
- [Synchronous vs Asynchronous Connector](https://arc.fuet.ch/concepts/integration/synchronous-vs-asynchronous-connector.md)
- [Connector Cardinality](https://arc.fuet.ch/concepts/fundamentals/connector-cardinality.md)
- [Connector Transparency (Direct vs Indirect Connection)](https://arc.fuet.ch/concepts/integration/connector-transparency.md)
- [File Transfer](https://arc.fuet.ch/concepts/integration/file-transfer.md)
- [Shared Database](https://arc.fuet.ch/concepts/integration/shared-database.md)
- [Remote Procedure Call](https://arc.fuet.ch/concepts/integration/remote-procedure-call.md)
- [Messaging](https://arc.fuet.ch/concepts/integration/messaging.md)

## Sources

- [Introduction to Integration Styles - Enterprise Integration Patterns](https://www.enterpriseintegrationpatterns.com/patterns/messaging/IntegrationStylesIntro.html) — enterpriseintegrationpatterns.com, accessed 2026-11-09
- [Messaging - Enterprise Integration Patterns](https://www.enterpriseintegrationpatterns.com/patterns/messaging/Messaging.html) — enterpriseintegrationpatterns.com, accessed 2026-11-09