Org.simantics.history

This plugin(org.simantics.history) contains a library for history service.

Details

HistoryManager manages persistent and stateful objects called "Subscription". Subscription has globally unique id (GUID).

When a subscription is recorded, it is opened and a handle is received. To record the user supplies time code and values for each variable.

A subscription consists of items that describe how a variable is to be recorded and stored in a file. For each item: interval, deadband, variableId, enabled, and the sample format are provided.

Sample format describes the format how the data is stored in the stream file, the primitive types and fields to record. There is a well-known set of fields that the recording supports. Unknown fields are left unchanged. Fields "time", "endTime", and "value" are mandatory.

Sample = {
  // Time
  time         : Double,      // Time of the first sample (mandatory field) 
  endTime      : Double,      // Time of the last sample (mandatory field)
 
  // Values
  value        : Double,      // First value (mandatory field)  
  lastValue    : Double,      // Last value 
  avg          : Double,      // Avg value of source valus within the band's time range
  median       : Double,      // Median value
  min          : Double, 
  max          : Double,
    
  count        : Integer      // The number of source values acquired 
}

One variable is typically subscribed with multiple items. For instance, simantics chart subscribes the chart_raw, chart_1s, chart_10s, chart_60s, and chart_min-max items. 1s, 10s, and 60s have corresponding interval value (eg. max. 1 entry per 10s of data). "min-max" is an subscription item that tracks down the minimum and maximum value of the variable. It has infinitely long interval value and thus records only one sample (unless there is discontinuation).

The sample entry is basically a band of values. The entry is packed even if deadband and interval are disabled. The system packs the unchanged set of values into a single entry.

Simple = {
  time         : Double, 
  endTime      : Double,
  value        : Double
}

The system can write down any primitive fields. Even arrays, enums, records and strings. Time and endTime fields must be numeric, values not.

Example1 = {
  time         : Long, 
  endTime      : Long,
  value        : Double,
  avg          : Float
}

VectorSample = {
  time         : Long, 
  endTime      : Long,
  value        : Double[ 3 ]
}

Discontinuity

The assumption is that two consecutive steram entries describe a data that is sampled continuously from the source. If there is non-continuation in the source data or if the recording was disabled temporarily, a discontinuation marker is added.

To support discontinuation in the data stream, the value-field must have Optional value.

Example = {
  time         : Long, 
  endTime      : Long,
  value        : Optional( Double )
}

Other value-fields need not be Optional().

File History

File based implementation is the only existing implementation. Files are managed in workarea (folder). Subscription state and recording metadata is in one file, and all subscription items each in a separate file.

Subscription        -    [SubscriptionId].dbb
SubscriptionItem    -    [SubscriptionId]-VariableId-[sampling hash hex]-[sampling name].stm

When a subscription is created, it prepares all related files. If a subscription is modified, it reflects to files by deleting and creating new.

An open subscription recording can be closed and opened, the state data is persisted when the handle is closed.