In many common uses of Mechanical Turk, you will want to ask many questions of the same kind, such as identifying an object in each of thousands of photos. A single Worker can answer one or many of these questions. To make it easy for Workers to find your HITs, Mechanical Turk groups similar HITs together, and Workers search and browse the groups. If a Worker qualifies for HITs in the group, the Worker may preview a single HIT, then accept it and begin work. When a Worker completes one HIT in a group, Mechanical Turk shows the Worker another HIT from the same group. Most Workers will complete many similar HITs in a single session.
Mechanical Turk groups HITs together based on their HIT type. A HIT type is defined by the values for a set of common properties. Two HITs with identical values for these properties are considered to be of the same HIT type, and appear in the same group on the Mechanical Turk web site.
Your application can use HIT types to manage different kinds of
work. Each HIT type has a HIT type ID, which your application
can use to query for HITs of a particular type. The HIT type ID
may also be used with the
operation in place of the common property values, to ensure that
the new HIT will be assigned the same type as other HITs.
The HIT properties that define a HIT type are the following:
A set of zero or more QualificationRequirements
You can explicitly register a new HIT type by calling the
operation. This operation
takes values for the common parameters, and returns a HIT type
ID for the type that matches the values. You can create HITs
using the new type by calling the
operation with the type ID, and values for the properties
specific to the HIT (such as the
You can create a HIT without specifying a HIT type ID by passing
values for the common parameters directly to the call to
. If the values match an existing
HIT type, the HIT will be given the existing type. If the
values do not match an existing HIT type, a new type is created
with those values. In either case, the HIT type ID is returned
with the HIT data in the response from the call to
To avoid accidentally passing mismatched values for two HITs
that ought to be part of the same type, register the HIT type
Once you have created a HIT, you might want to change the HIT type. Use the ChangeHITTypeOfHIT operation to do this.
HITs of the same HIT type can have differing values for the following properties: