An explorer in KE-chain is a representation of an actual, physical product defined by a given data model. A product consists of a large number of parts with a hierarchical ordering which is determined by the data model. Analogous to part models in a data model, parts in a product can be nested indefinitely.
Parts in the explorer are instantiated based on the part models in the data model. This is why sometimes they are also called part instances. Also, a part instance without part model cannot exist. The amount of parts that can be created based on a model is strictly controlled by the quantity that is set on the part model upon creation. All the properties created in the data model will be replicated exactly in the parts inside the explorer.
The figure below shows an example of a product defined in the explorer, called the Yes!Delft office, KE-works headquarters and where KE-chain was born. The product is based on the data model example provided here, which means that the number of parts (part instances) in the explorer tree is consistent with the quantity defined for the corresponding part models inside the data model.
Auto-instantiation is strictly connected to the quantity concept. Read about it on the Concept: Part concept page.