====== Database design ======

===== Overview =====

The structure of the database is hierarchical. The data is organized into projects. Each project can be seen as a database of its own – data is not shared between projects.\\
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Parameters are described using [[Parameter_definition|definitions]]. Each type of parameter has a definition which determines its name, [[Units|unit]] and [[Dependencies_(Parameter_database)|dependencies]] as well as some general information about the parameter. The definition is identified by its [[Name|name]]; within a project there may not be two definitions with the same name.\\
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Values for specific type of parameter are stored in an [[Parameter_instance|instance]]. A chosen definition states the name, unit and dependencies of the parameter values. In order to identify the instance it can be given search [[Tag|tags]]. An instance can be seen as a set of values for a specific type of parameter and a specific case or scenario.\\
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The instance has one [[Parameter_entry|entry]] for each dependency. A parameter entry (may) contain a nominal value, a probability density function as well as statistics such as mean value, min, max and number of samples.\\
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**For example:** The distribution coefficient for soil is defined in the project as Kd_soil. The definition states that Kd_soil depends on atomic element and that it is unitless. When investigating different scenarios, different sets of values for Kd_soil are used. Hence, for each scenario an instance of Kd_soil is created. Each instance is tagged with the name of the scenario, and data is filled in for each atomic element relevant to the scenario.\\
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**See also:**

  * [[Dependencies_(Parameter_database)|Dependencies]]
  * [[Users and roles]]
  * [[Quality assurance]]

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