The key differences between this operation and simply searching the group's patients compartment are:

• unless the client requests otherwise, the server returns the entire result set in a single bundle (rather than using paging)
• the server is responsible for determining what resources to return as included resources (rather than the client specifying which ones).

This frees the client from needing to determine what it could or should ask for, particularly with regard to included resources.

It is assumed that the server has identified and secured the context appropriately, and can either associate the authorization context with a particular group, or determine whether the context has the rights to the nominated group, if there is one, or can determine an appropriate list of groups to provide data for from the context of the request. If there is no nominated group (GET /[base]/Group/$everything) and the context is not associated with a single group record, the actual list of groups is all groups that the user associated with the request has access to. In such cases, the server may choose to return an error rather than all the records (and is likely to do so, but not required to). Specifying the relationship between the context, a user and groups is outside the scope of this specification (though see The SMART App Launch Implementation Guide).

The return bundle from this operation is usually rather a lot of data; servers typically choose to require that such requests are made asynchronously, and associated with bulk data formats. Alternatively, clients may choose to page through the result set (or servers may require this). Paging through the results is done the same as for Searching, using the _count parameter, and Bundle links. Implementers should note that paging will be slower than simply returning all the results at once (more network traffic, multiple latency delays) but may be required in order not to exhaust available memory reading or writing the whole response in a single package. Unlike searching, there is no inherent user-display order for the $everything operation. Servers might consider sorting the returned resources in descending order of last record update, but are not required to do so.

The _since parameter is provided to support periodic queries to get additional information that has changed about the group since the last query. This means that the _since parameter is based on record time. The value of the _since parameter should be set to the time from the server. If using direct response, this is the timestamp in the response header. If using the async interface, this is the transaction timestamp in the json response. Servers should ensure that the timestamps a managed such that the client does not miss any changes. Clients should be able to handle getting the same response more than once in the case that the transaction falls on a time boundary. Clients should ensure that the other query parameters are constant to ensure a coherent set of records when doing periodic queries.