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OpenHamony supports synchronization of the relational data of an application across multiple devices.
OpenHamony supports synchronization of the relational data of an application across multiple devices.
- Distributed table list<br>After a table is created for an application in an RDB store, you can set it as a distributed table. When querying the RDB store of a remote device, you can obtain the distributed table name of the remote device based on the local table name.
- Distributed table list
- Synchronization mode<br>Data can be synchronized between devices in either of the following ways: <br>- Pushing data from a local device to a remote device. <br>- Pulling data from a remote device to a local device.
After a table is created for an application in an RDB store, you can set it as a distributed table. When querying the RDB store of a remote device, you can obtain the distributed table name of the remote device based on the local table name.
- Synchronization mode
Data can be synchronized between devices in either of the following ways:
- Pushing data from a local device to a remote device.
- Pulling data from a remote device to a local device.
## Working Principles
## Working Principles
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- Each RDB store supports a maximum of eight callbacks for subscription of data change notifications.
- Each RDB store supports a maximum of eight callbacks for subscription of data change notifications.
- Third-party applications cannot call the distributed APIs that must be specified with the device.
## Available APIs
## Available APIs
The following table lists the APIs for cross-device data synchronization of RDB stores. Most of the APIs are executed asynchronously, using a callback or promise to return the result. The following table uses the callback-based APIs as an example. For more information about the APIs, see [RDB Store](../reference/apis/js-apis-data-relationalStore.md).
Most of the APIs for cross-device data synchronization of RDB stores are executed asynchronously in callback or promise mode. The following table uses the callback-based APIs as an example. For more information about the APIs, see [RDB Store](../reference/apis/js-apis-data-relationalStore.md).
| API| Description|
| API| Description|
| -------- | -------- |
| -------- | -------- |
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1. Request the **ohos.permission.DISTRIBUTED_DATASYNC** permission. For details, see [Declaring Permissions in the Configuration File](../security/accesstoken-guidelines.md#declaring-permissions-in-the-configuration-file).
1. Request the **ohos.permission.DISTRIBUTED_DATASYNC** permission. For details, see [Declaring Permissions in the Configuration File](../security/accesstoken-guidelines.md#declaring-permissions-in-the-configuration-file).
2. Display a dialog box to ask authorization from the user when the application is started for the first time. For details, see [Requesting User Authorization](../security/accesstoken-guidelines.md#requesting-user-authorization).
2. Display a dialog box to ask authorization from the user when the application is started for the first time. For details, see [Requesting User Authorization](../security/accesstoken-guidelines.md#requesting-user-authorization).
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> **NOTE**
> **NOTE**
>
>
> **deviceIds** is obtained by using [devManager.getTrustedDeviceListSync](../reference/apis/js-apis-device-manager.md#gettrusteddevicelistsync). The APIs of the **deviceManager** module are all system interfaces and available only to system applications.
> The value of **deviceIds** can be obtained by [deviceManager.getAvailableDeviceListSync](../reference/apis/js-apis-distributedDeviceManager.md#getavailabledevicelistsync).