CaosDB is a database management system that stores it's data into `Entities`. An `Entity` can be thought of as the equivalent to tables, rows, columns and the tuples that fill the tables of a traditional RDBMS. Entities are not only used to store the data they also define the structure of the data.
# Formal Definition
An `Entity` may have
* a `domain`
* an `id`
* a `role`
* a `name`
* a `data type`
* a `Set of Values`
* a `Set of Properties`
* a `Set of Parents`
A `domain` contains an `Entity`.
An `id` is an arbitrary string.
A `role` is an arbitrary string. Especially, it may be one of the following strings:
*`RecordType`
*`Record`
*`Relation`
*`Property`
*`File`
*`QueryTemplate`
*`Domain`
*`Unit`
*`Rule`
*`DataType`
*`Remote`
A `name` is an arbitrary string.
A `data type` contains an `Entity`. Note: this is not necessarily a `Data Type`.
## Set of Values
A `Set of Values` is a mapping from a `indices` to a finite set of `Values`.
An `index` is an interval of non-negative integers starting with zero.
### Value
A `Value` may have a `data type` and/or a `unit`.
A `data type` is an `Entity`. Note: this is not necessarily a `Data Type`.
A `unit` is an arbitrary string.
## Data Type
A `Data Type` is an `Entity` with role `DataType`.
### Reference Data Type
A `Reference Data Type` is a `Data Type`. It may have a `scope`.
A `scope` contains an `Entity`.
### Collection Data Type
A `Collection Data Type` is a `Data Type`. It may have an ordered set of `elements`.
## Record Type
A `Record Type` is an `Entity` with role `RecordType`.
## Record
A `Record` is an `Entity` with role `Record`.
## Relation
A `Relation` is an `Entity` with role `Relation`.
## Property
A `Property` is an `Entity` with role `Property`. It is also refered to as `Abstract Property`.
## File
A `File` is an `Entity` with role `File`.
A `File` may have
* a `path`
* a `size`
* a `checksum`
A `path` is an arbitrary string.
A `size` is a non-negative integer.
A `checksum` is an ordered pair (`method`,`result`).
A `method` is an arbitrary string.
A `result` is an arbitrary string.
## QueryTemplate
A `QueryTemplate` is an `Entity` with role `QueryTemplate`.
## Domain
A `Domain` is an `Entity` with role `Domain`.
## Unit
A `Unit` is an `Entity` with role `Unit`.
## Rule
A `Rule` is an `Entity` with role `Rule`.
## Remote
A `Remote` is an `Entity` with role `Remote`.
## Set of Parents
A `Set of Parents` is a set of `Parents`.
### Parent
A `Parent` may contain another `Entity`.
A `Parent` may have an `affiliation`.
An `affiliation` may contain of the following strings:
*`subtyping`
*`instantiation`
*`membership`
*`parthood`
*`realization`
## Set of Properties
A `Set of Properties` is a tripple (`index`, set of `Implemented Properties`, `Phrases`).
An `index` is a bijective mapping from an interval of non-negative integer numbers starting with zero to the set of `Implemented Properties`.
### Implemented Property
An `Implemented Property` contains another `Entity`.
An `Implemented Property` may have an `importance`.
An `Implemented Property` may have a `maximum cardinality`.
An `Implemented Property` may have a `minimum cardinality`.
An `Implemented Property` may have an `import`.
An `importance` is an arbitrary string. It may contain of the following strings:
*`obligatory`
*`recommended`
*`suggested`
*`fix`
A `maximum cardinality` is a non-negative integer.
A `minimum cardinality` is a non-negative integer.
An `import` is an arbitrary string. It may contain of the following strings:
*`fix`
*`none`
### Phrases
`Phrases` are a mapping from the cartesian product of the `index` with itself to a `predicate`.
