Abstract: A distributed database system and associated methods maintain historical data regarding an entity, such as a person or an object, in a tag or other object in association with the entity. The data proper is maintained with the entity and the data rules used to interpret the data proper are maintained at a separate location. The data proper maintained with the entity is stored in a manner to reduce the amount of memory space required. The data proper maintained with the entity is effectively encrypted from parties that do not have access to the data rules. The data proper may be converted to a fixed form, such as a bar code label, and attached to the entity to permit historical information to be ascertained at a later time.

Abstract: A pet door including a cammed closing mechanism and a sliding lock mechanism. The cammed closing mechanism returns the pet door to a resting closed position and provides sufficient force to resist opening by normal weather conditions such as wind or a hard rain without the need for additional components such as magnets. The sliding lock mechanism serves to control the ingress and/or the egress of an animal through the pet door as selected by the pet door owner.