====== Data Identification ======

Every variable stored in Mervis DB is identified by set of keys and values. Combination of of keys and values marked with attribute "IsKey=true" defines unique identification of variable (equivalent to **primary key** known from SQL world).

==== Keys ====

Any string that consists of characters: a-z, A-Z, 0-9, ., _, - can be used as a key. The key must not start with underscore ("_") character and must not be empty.

==== Values ====

Any string that consists of characters: a-z, A-Z, 0-9, ., _, - can be used as a value.



===== Recommended Keys =====

It's recommended to use the following structure of keys and values for new projects and Mervis DB clients.

^Key^Value^IsKey^Description^
| DataSource | "MyDS" | False |Unique identification of the particular data source type. |
| Root | "MyDsServer1" | **True** |Unique identification of the particular Mervis DB client. |
| Guid| "var546" | **True** |Unique identification of variable generated by Mervis DB client. |
| Level1 | "MyLevel1Id" | False | |
| Level2 | "MyLevel2Id" | False | |
| Level3 | "MyLevel3Id" | False | |
| Level4 | "MyLevel4Id" | False | |
| Level5 | "MyLevel5Id" | False | |
| Name | "My Variable" | False | |
| Unit | "m3" | False | |


==== Example ====
 
^Key^Value^IsKey^Description^
| DataSource | "SCADASystemXY" | False |Unique identification of the particular data source type. |
| Root | "Server18" | **True** |Unique identification of the particular Mervis DB client. |
| Guid| "aaaaa-bbbbb-ccccc-ddddd-eeeee" | **True** |Unique identification of variable generated by Mervis DB client. |
| Level1 | "SiteNr500" | False | |
| Level2 | "Building A" | False | |
| Level3 | "Floor 7" | False | |
| Level4 | "Room 17" | False | |
| Level5 | "SouthEast" | False | |
| Name | "Indoor Temperature" | False | |
| Unit | "C" | False | |