Each time a stream query or stream listener is activated it might be processing more than one item at a time. Each simultaneously processed group of items is referred to as a lot. Like an auction lot, a lot can contain just one item or it can contain a number of items. Stream listeners can be activated once per item or once per lot. Stream queries try to process each item in a lot as if it arrived separately. See Behavior of stream queries with lots for a discussion of cases where this is not possible.

When a lot contains multiple items all items in the lot appear in the output stream at the same time. However, the correlator preserves the order in which the stream query generated the items in the lot. When that output stream is the input stream for another stream query, the subsequent query uses the preserved order, if necessary, to determine how to process the items.