Database

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.

arch_object sample site_phase on_site material species meas site site_t period typo eco feature_t c14_meas reference lab country fell_phase

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: xronos_erd.dia (this file can be opened and edited with the diagram editor software Dia)