=History and Collector in Charts and Trends=
There is a specified way how trend manages the items in the history. 
The "id"-field of an history item has the following format: "subscriptionId-variableId-formatId". 
Therefore the files are named in the same notation (appended with the different extensions ".data", ".txt", ".index").

The trend's history item format has the following record:
 {
     id : String,
     variableId : String,         // Simantics RVI
     format : Datatype,
     deadband : Double,           // NaN = No deadband
     interval : Double,
     gain : Double,
     bias : Double,
     enabled : Boolean,
     groupId : String,            // Subscription Id
     groupItemId : String,        // Subscription Item Id
     formatId : String            // One of: "all", "100ms", "1s", "10s", "60s", or "minmax"
 }


Each datasource variable is sampled into 5-6 separated files with different interval. 
The sampling formats are named. Some formats may be omited if subscription configuration suggests so. For example, if "subscription interval = 250ms" then, the files "all" and "100ms" are omited.
{| border="1" cellpadding="3" cellspacing="0" align="center"
|- style="background-color: #f9f9f9;"
|'''SamplingFormat-Id'''
|'''Description'''
|- 
|"all"
|All datasource samples are stored here.
|-
|"100ms"
|Samples are written with (atleast) 100ms interval.   
|-
|"1s"
|Samples are written with (atleast) 1000ms interval.
|-
|"10s"
|Samples are written with (atleast) 10000ms interval.
|-
|"60s"
|Samples are written with (atleast) 60000ms interval.
|-
|"minmax"
|File contains only one sample and it has fields { time, value, endTime, min, max }. Not used for with binary variable.
|}

The file format for analog variables is the following:
{| border="1" cellpadding="3" cellspacing="0" align="center"
|- style="background-color: #f9f9f9;"
|'''SamplingFormat-Id'''
|'''Sample RecordType'''
|- 
|"all"
|{ time:Double, endTime:Double, value:Double, quality:Byte }
|-
|"100ms"
|{ time:Double, endTime:Double, value:Double, min:Double, max:Double, avg:Double, quality:Byte }   
|-
|"1s"
|{ time:Double, endTime:Double, value:Double, min:Double, max:Double, avg:Double, quality:Byte }
|-
|"10s"
|{ time:Double, endTime:Double, value:Double, min:Double, max:Double, avg:Double, quality:Byte }
|-
|"60s"
|{ time:Double, endTime:Double, value:Double, min:Double, max:Double, avg:Double, quality:Byte }
|-
|"minmax"
|{ time:Double, endTime:Double, value:Double, min:Double, max:Double }
|}

The file format for binary variables is the following:
{| border="1" cellpadding="3" cellspacing="0" align="center"
|- style="background-color: #f9f9f9;"
|'''SamplingFormat-Id'''
|'''Sample RecordType'''
|-
|"all"
|{ time:Double, endTime:Double, value:Byte, quality:Byte }
|-
|"100ms"
|{ time:Double, endTime:Double, value:Byte, max:Byte, quality:Byte }   
|-
|"1s"
|{ time:Double, endTime:Double, value:Byte, max:Byte, quality:Byte }
|-
|"10s"
|{ time:Double, endTime:Double, value:Byte, max:Byte, quality:Byte }
|-
|"60s"
|{ time:Double, endTime:Double, value:Byte, max:Byte, quality:Byte }
|}