# Advanced services
The Trusted Twin platform offers a series of advanced services. These services are:
- the History service (stores historical values of Ledger entries),
- the Timeseries service (stores structured and multidimensional views of Twin history),
- the Indexes service (stores structured and multidimensional views of Twin states),
- the Notifications (publish/notify) service,
- the Stickers (workflow tags) service.
The historical values, as well as the current value of the Entry, can be viewed at any time by sending a request to the get_twin_ledger_entry_history endpoint. The response returns a list of Entries with the history of Entry value changes in form of key-value pairs:
A Timeseries database on the Trusted Twin platform stores structured and multidimensional views of Twin history in form of user-defined tables created through the create_timeseries_table endpoint. A Timeseries database consists of one or more tables.
On the right-hand side you can find an example of a Timeseries table which contains a timestamp column (added automatically by the system), one dimension ("city") and three measurements ("temperature", "ozone", "relative_humidity"):
A Timeseries table is automatically updated each time an Entry with a
"timeseries" attribute for the given Timeseries table is being changed.
The Timeseries database service needs to be enabled for your account. Please contact email@example.com for more details.
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Indexes* allow you to efficiently access Ledger records and are especially helpful if you manage a large number of Twins within your account. The Indexes database on the Trusted Twin platform stores structured and multidimensional views of Twin states in form of user-defined tables created through the create_indexes_table endpoint. An Indexes database consists of one or more tables. An Index can occur only once in a given Twin.
On the right-hand side you can find an example of an Indexes table which contains a Twin column (stating the UUID of the Twin where the index occurs), a timestamp column stating when the index was last changed (added automatically by the system), and three properties (
The Indexes service needs to be enabled for your account. Please contact firstname.lastname@example.org for more details.
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Notifications allow to automatically invoke external services via publish/notify service (e.g., webhooks). Notifications can be triggered by the following events:
Stickers (workflow tags) are a functionality designed to facilitate workflow processes. They support passing ownership of workflow items (e.g., tasks to be done) between multiple users.