# Interface Apps: Integration with External Systems

**Interface Apps** are applications that use ONEWEB primarily as an **integration layer**.\
In this design pattern, the application focuses on **connecting systems, exchanging data, and exposing services**, rather than providing rich user interfaces or complex user‑driven workflows.

Interface Apps are commonly used to:

* Integrate internal application components
* Connect ONEWEB with external systems
* Expose services or APIs for other systems to consume

ONEWEB provides built‑in integration capabilities and supports **Microflow** as the core mechanism for implementing integration logic.

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#### Role of Microflow in Interface Apps

In Interface Apps, **Microflow** acts as the orchestration and execution layer that:

* Receives requests from external systems
* Transforms and validates data
* Coordinates interactions between systems
* Sends responses back to consumers

Microflows allow integration logic to be designed visually and managed consistently within the ONEWEB platform.

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#### Common Integration Design Patterns

The following are the most common **integration patterns** implemented using Microflow in ONEWEB.

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**Web Service Integration**

Use this pattern when:

* External systems communicate using **web services or APIs**
* ONEWEB needs to expose services for other systems
* Real‑time request/response interaction is required

Typical use cases include:

* REST or SOAP service integration
* API gateways
* Real‑time system‑to‑system communication

This is the most common integration pattern in modern architectures.

***

**File‑Based Integration**

Use this pattern when:

* Systems exchange data using **files**
* Integration is batch‑oriented rather than real‑time
* Legacy systems are involved

Typical use cases include:

* Importing or exporting data files
* Scheduled batch processing
* Integration with systems that do not support APIs

File‑based integration is often used when system constraints limit direct connectivity.

***

**Java‑Based Integration**

Use this pattern when:

* Custom logic or libraries are required
* Integration requires complex processing
* Existing Java components need to be reused

Typical use cases include:

* Custom adapters
* Specialized transformation logic
* Integration with proprietary Java‑based systems

This pattern provides flexibility while still operating within the ONEWEB platform.

***

**Database‑Level Integration**

Use this pattern when:

* Systems share or exchange data through **databases**
* Direct database access is required
* Integration is tightly coupled at the data level

Typical use cases include:

* Data synchronization
* Reporting or data replication
* Integration with systems that expose data only through databases

This pattern should be used carefully to maintain data consistency and integrity.

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#### Design Guidance for Interface Apps

As part of **App Design Fundamentals**, consider the following when designing Interface Apps:

* Prefer **service‑based integration** over tight coupling
* Use file‑based or database integration only when APIs are not available
* Keep integration logic **modular and reusable**
* Design Microflows to be **clear, testable, and maintainable**

Interface Apps often operate without user interaction, so **reliability, performance, and error handling** are critical design considerations.


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