15. One or more computer-storage media storing a first schema for describing a data store, the first schema being useable to interact with the data store, the first schema comprising: a property description element describing a first property of the data store, the property description element including both static attributes that describe the first property for any schema having the first property and contextual attributes that describe the first property only for the first schema, wherein each static attribute has a corresponding static attribute value and each contextual attribute has a corresponding contextual attribute value wherein a static attribute associated with the first individual property is immutable and has the same static attribute value within all schemas that include the first individual property, wherein a contextual attribute is able to have different contextual attribute values among different schemas that include the first individual property, and wherein contextual attribute values are defined within each schema that has the contextual attribute; a property reference element describing a second property of the data store by referencing a second property description element from a second schema that includes static attributes and corresponding static attribute values, wherein the property reference element specifies contextual attributes and corresponding contextual attribute values, wherein the static attributes apply to all schemas that reference the second property description, and wherein the contextual attributes apply only to the first schema an item type description element describing an item type for at least one item in the data store, the item type description element including one or more properties that define the item type; and a kind description element describing a kind for at least one item in the data store, the kind description element including one or more properties for the kind, wherein the kind is a collection of logically related item types.
16. The one or more computer-storage media of claim 15 , wherein the property description element includes a related property element that defines a relationship between the property description element and another property description element wherein the related property element includes attributes to identify related property description elements and describe a type of relationship between property descriptions elements.