The general logic of the xronos.rails database is best understood from the perspective of the
arch_object entity. Archaeological objects are dated artefacts or samples with
archaeological context information.
The database was modelled with an Entity Relationship (ER) diagram:
Some help on how to read this chart:
Boxes: Entity. An entity is a class of objects in the real world (e.g. *archaeological sites*)
that can be described with a set of attributes (e.g. *name, number of documented houses, spatial
position*). All entities will become tables in database.
Diamonds: Relationship. Relationships describe the relations and interaction of entities
(e.g. the *radiocarbon laboratory* is linked to the *sample* via the process of *measurement*).
Some relationships have additional arguments (the *measurement* produces a *labnr*, happens at
a certain *time* and has a specific *price* tag). Some relationships will become tables in the
database, others won't. That depends on the nature of the relationship.
Lines: Lines connect entities and relationships. Each line has a label to describe the amount
of objects within an entity that can or have to be part of that relationship. Some examples:
*(0,\*)*: Zero or many objects can be part of that that relationship. *(1,1)*: Exactly one object
can be part of that relationship. That also implies that each object has to have exactly one
partner in this specific relationship. *(0,1)*: Each object linked to the relationship has zero or
one partner within the other linked entity.
The source file for this visualisation can be found here:
(this file can be opened and edited with the diagram editor software Dia)