> ## Documentation Index
> Fetch the complete documentation index at: https://docs.seam.co/llms.txt
> Use this file to discover all available pages before exploring further.

# Architecture

> A high-level view of how the Seam iOS SDK integrates with your app, Seam Cloud services, and lock hardware — including data flow, security, and offline support.

## System Components

SeamSDK connects four main components:

* **Mobile App** — Your iOS application, written in Swift, that calls the Seam SDK.
* **SeamSDK** — A native library responsible for credential management, unlock flows, and event streaming.
* **Seam Cloud API** — The cloud service that provisions credentials, handles revocation, and provides analytics.
* **Lock Hardware** — Physical locks that communicate over BLE and/or NFC.

```
Mobile App  ──SDK Calls──▶  Seam SDK  ──HTTP──▶  Seam Cloud API
                               │                       │
                           BLE/NFC               Push Events
                               │                       │
                               ▼                       ▼
                          Lock Hardware          Seam SDK (update)
```

***

## Unlock Sequence

The following sequence shows what happens from initialization through a successful unlock:

<Steps>
  <Step title="Initialization">
    Your app calls `Seam.initialize(clientSessionToken:)` and then `activate()`.
  </Step>

  <Step title="Credential Fetch">
    The SDK automatically fetches and keeps credentials up to date by syncing with Seam Cloud.
  </Step>

  <Step title="Unlock Request">
    Your app invokes `unlock(using: credentialId)`.
  </Step>

  <Step title="Connection">
    The SDK connects to the lock via BLE or NFC.
  </Step>

  <Step title="Authentication and Confirmation">
    The lock authorizes the credential and responds.
  </Step>

  <Step title="Event Stream">
    The SDK emits `SeamUnlockEvent` values: `launched`, `grantedAccess`, and others.
  </Step>

  <Step title="Completion">
    Your app handles the events and updates its UI accordingly.
  </Step>
</Steps>

***

## Key Data Types

| Type                           | Description                                                                                                                                                                       |
| ------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Client Session Token (CST)** | A short-lived token used to authenticate SDK API calls. Obtained from your server via the Seam API.                                                                               |
| **SeamCredential**             | Represents a single access credential with `id`, `name`, `location`, `expiry`, and `metadata`. Immutable snapshot; observe the `credentials` published property for live updates. |
| **SeamUnlockEvent**            | Enum describing each stage of an unlock operation (`launched`, `grantedAccess`, `timedOut`, `connectionFailed`).                                                                  |
| **SeamError**                  | Thrown for SDK setup and API-level failures. See [Error Handling](/mobile-sdks/ios/error-handling).                                                                               |
| **SeamCredentialError**        | Returned when a specific credential has an issue (expired, unsupported device, user interaction required).                                                                        |

***

## Security and Offline Support

* **Secure Transport** — All API calls use HTTPS. Lock communication is secured by the lock vendor's protocol.
* **Keychain Storage** — Tokens and other sensitive data are stored in the iOS Keychain.
* **Offline Support** — SeamSDK supports offline usage. Credentials are cached locally so that unlock attempts and recent credential data remain available during network interruptions.

***

## See Also

* [Quickstart](/mobile-sdks/ios/quickstart) — How to initialize SeamSDK and perform your first unlock.
* [Error Handling](/mobile-sdks/ios/error-handling) — How to interpret and handle errors emitted by SeamSDK.