Backend FAQ

This page covers backend, database, API, and push notification questions. For general Cozie AppStore questions, see the FAQ. For source-code customization and custom app development questions, see the App Developer FAQ.

Data and internet access

• Where is Cozie data stored?

  Cozie offers two ways to store data:

  1. Default
     By default, Cozie-Apple data is stored on password-protected servers in Singapore and logged on the iPhone. The data can be downloaded from our online API. Data data can also be retrieved from the local backup file.

  2. Custom Database
     Instead of using our database to store your data, you can also set up your own backend. Just replace the necessary API information in the Advanced tab and you can operate the Cozie app independent of us. No changes to the source code are required.  

Performance

• How long does it take for a push notification from OneSignal to arrive on the iPhone or Apple Watch?

  Provided there is an internet connection, it usually takes less than ten seconds between sending a push notification, and the push notification appearing on the iPhone and/or the Apple Watch.

• How frequently is the physiological data logged?

  It is important to distinguish two terms: logging rate and sampling rate. The sampling rate is defined by the time between to measurement samples. The logging rate is defined by the points in time when the measurement samples were sent to the database.

  Example:

  time	ts_heart_rate	ts_heart_rate_lambda	ts_heart_rate_trigger
  2023-10-10 12:49	76	2023-10-10 12:53	background_task
  2023-10-10 12:52	75	2023-10-10 12:53	background_task
  2023-10-10 12:55	77	2023-10-10 13:15	application_appear

  The table above shows three samples of a heart rate measurement (ts_heart_rate). The ts_heart_rate column shows the value of the measurement in beats per minute (bpm).

  The time column shows when the measurement took place.

  The ts_heart_rate_lambda column shows the timestamp of when the sample was inserted into the database (logged).

  The ts_heart_rate_trigger column records what triggered the Cozie app to send the data.

  In this example, the timestamps in time are three minutes apart. Hence, the sampling rate is 1 sample per 3 minutes.

  The first two rows were logged at the same time (tes_heart_rate_lambda). The third row was logged 23 minutes later. Hence, the logging rate is 1 log per 23 minutes. The sampling rate cannot be influenced and is given by the data provided by iOS. The logging rate can be influenced, e.g., by opening the app, using the iPhone, and taking watch surveys.

• Is it possible to call the function that pulls the GPS location, heart rate data, etc., in a set interval without the participant interacting with the survey?

  Well, having a live stream of all data is the dream. We've been working hard on that dream for a while. Here is the result: All HealthKit data is submitted twice:

  1. When the watch survey is submitted. In that case, the prefix is ws_, e.g., ws_heart_rate.
  2. Then the HealthKit data is submitted a second time with the prefix ts_, e.g., ts_heart_rate.

  ts_ data has various triggers, e.g., when you open the app, when you press the sync buttons in the app, and sometimes it is sent in the background.

  You can check what triggered the transmission of the data and when it arrived in the database with the fields with the postfix _trigger and _lambda, e.g., ts_heart_rate_trigger and ts_heart_rate_lambda or ws_heart_rate_trigger and ws_heart_rate_lambda.

  You can increase the chances of the data being sent by using the iPhone. Because Cozie can only access HealthKit data when the phone is unlocked. But in our experience, the ws_ data has the highest update frequency, provided participants are reminded every hour and also provide a watch survey response accordingly.

  For the location, you already know about ws_latitude and ws_longitude. There is also ts_latitude, and ts_longitude. These location data are sent when the user changes their location.

Push notifications

• What is the maximal length of a push notification?

  There are no hard limits on the length of a push notification. OneSignal states the following (Source):

  • Title: About 25-50 character limit
  • Message: About 150 characters limit

  In any case, you must draft push notifications and test them on an Apple Watch to see whether they work as expected.

• How many push notifications can be shown in a push notification?

  There are no hard limits on the number of action buttons. OneSignal states the following (Source):

  • iOS supports up to 4 buttons with Rich Notifications

  However, in our own testing, we have seen that the action button payload can be up to 255 bytes, and one action button requires at least 22 bytes (1 ID character, 1 text character). Hence, the maximum number of action buttons with only one text character is eleven. Longer texts or IDs will result in fewer action buttons.

  In any case, you must draft push notifications with action buttons and test them on an Apple Watch to see whether they work as expected.