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Understanding Hydra 2.0: The Hydra data model
The Basics
The Hydra data model is based upon the hierarchical structure of a tree. The root node of the tree is the ConfigRoot. Each tree node may have sub-nodes, these are the ConfigKeys. Each ConfigKey may have values, these are the ConfigValues. The label of ConfigKeys and ConfigValues must be unique among their siblings. Together with permission and selection restrictions, these elements form the Hydra data model.
The ConfigRoot
The ConfigRoot is the root of the Hydra tree. It may not have any values, but is the parent of ConfigKeys. Being the parent of ConfigKeys, it is possible to set the key permission and key selection mode for the ConfigRoot.
The ConfigKey
The ConfigKey elements form the nodes of the Hydra tree. They may have ConfigKeys as their children. Additionally, they may have ConfigValues. Hence, the key permission, key selection mode, value permission and value selection mode can be set for each ConfigKey.
The ConfigValue
ConfigValues belong to a ConfigKey. Based upon the user selection one ConfigKey may have different active ConfigValues.
The key permissions
| Permission | Meaning |
|---|---|
| READ_KEYS | The child ConfigKeys may only be read. |
| MODIFY_KEYS | The label of child ConfigKeys may be altered. |
| WRITE_KEYS | The label of child ConfigKeys may be altered. Child ConfigKeys may be added and even be deleted. |
The key selection modes
| Selection mode | Meaning |
|---|---|
| 1 | Only one child ConfigKey may be active. |
| MINIMUM (?...n) | At least ? child ConfigKeys must be active. |
| MAXIMUM (0...?) | At most ? child ConfigKeys may be active. |
| FIXED | It is not possible to change the selection via the Hydra GUI in an application. |
| NULL | Child ConfigKeys may arbitrarily be selected and unselected. |
The value permissions
| Permission | Meaning |
|---|---|
| READ_VALUES | The ConfigValues may only be read. |
| MODIFY_VALUES | The label of ConfigValues may be altered. |
| WRITE_VALUES | The label of ConfigValues may be altered. ConfigValues may be added and even be deleted. |
The value selection modes
| Selection mode | Meaning |
|---|---|
| 1 | Only one ConfigValue may be active. |
| MINIMUM (?...n) | At least ? ConfigValues must be active. |
| MAXIMUM (0...?) | At most ? ConfigValues may be active. |
| FIXED | It is not possible to change the selection via the Hydra GUI in an application. |
| NULL | ConfigValues may arbitrarily be selected and unselected. |
| next section: Understanding Hydra 2.0 The Hydra API |