Harvest Gatherers and Brokers communicate using an attribute-value stream protocol called the Summary Object Interchange Format (SOIF), an example of which is available here. Gatherers generate content summaries for individual objects in SOIF, and serve these summaries to Brokers that wish to collect and index them. SOIF provides a means of bracketing collections of summary objects, allowing Harvest Brokers to retrieve SOIF content summaries from a Gatherer for many objects in a single, efficient compressed stream. Harvest Brokers provide support for querying SOIF data using structured attribute-value queries and many other types of queries, as discussed in Section 5.3.