Using E-Tags

An Entity Tag (or E-Tag) is an identifier for a version of data. It is a mechanism that uses caching to reduce the load on the server.

The E-Tag header provides a means for consuming systems to check if any cache they are keeping is up to date. You can query requests for data that return an E-Tag response header again, using the same E-Tag header value in the request. If the server detects no changes since the E-Tag, it will return a 304 response code with an empty body. This means the data has not changed.

A 304 response code with an empty body, indicates no changes to the data was made since the E-Tag was issued. If the data changes, the system will return only the differences between the requested E-Tag and the current state. It will include a new E-Tag in the response header.

Example

In our implementation, if you request the field boundary information, the server sends it to you.

If the API gets the same request again, it will reply with a 304 response code. It will not provide any data if it has not updated since the last request.

Below is a table of how key-value pairs would look like in this scenario:

Key	Value
Ocp-Apim-Subscription-Key	{{Ocp-Apim-Subscription-Key}}
ETag	fb16c641-1b17-43e5-af95-4d0edab94...
Authorization	Bearer {{AccessToken}}