Wikidata data validation

Wikidata data must be validated.

Still it is only eventually complete; which is a theoretical status, because it will never be attained.

Characteristics

Items and properties have unique and immutable keys
Triplestore database with statements (predicates) consisting of object-property-subject/value pairs (entity relationship like in a relational database)
Easily updateable (simple concept; user driven data model)
Never 100% complete nor correct (eventual consistent)
Multilingual:
- Labels, Descriptions, and Aliases are language sensitive
- Properties are described like items (Property namespace)
  - New properties can be defined (by developers, upon user request, and approval)

Items must be unique
- Unique Label - Description combination (homonym distinction)
- Description must be different from Label
- Label can not be repeated in Alias
Items must either have an instance or a class
Notability:
1. Item could be created because a Wikipedia page exists
2. notoriety
3. Item is required to describe another item
Labels in lowercase (nouns) or initial capital (proper names) -- i.e. German is an exception
Add sources (references) to statements (more information, proof of validity)
Use (P6104) (maintained by WikiProject) to list related items
- Can be used by ListeriaBot to build Wikipedia edit-a-thon and project tables/lists

Constraints:
- additional classes might be added
- reciproque property
- reverse property
Missing language labels
Homonym dedection and (P1889) registration