streamAttribute

Owned by Former user (Deleted)
Oct 06, 2015
2 min read

Forms: Stream Attribute

Stream Attributes define the type, precision and expressions of how each individual attribute is calculated based on the inputs to the Stream.

Stream attributes are listed in the Stream Attributes tab in the Stream Details form.

The following details are configured for each stream attribute:

Form: Stream Attribute Details

Field Description
Name Name of the Attribute.
Type This can be one of:
  • String
  • Integer
  • Float
  • Date
  • Datetime
  • TrueFalse
Local Tick this if this field is only required as part of the stream calculation, and it is not necessary to keep the result for further stream calculations, reports or alarms. If this is ticked, the Column Name field becomes optional.
Length/Precision For a String, the maximum length of the String. For an Integer, the maximum number of digits.
Order The order in which the attributes are placed in the stream.
Expression The expression used to generate the attribute value. This is written as a CenterView Expression.
Cache Key If a cache key is set, the value of this attribute persists throughout the stream calculation, rather than being created from scratch for each stream item as normal. This allows you to keep track of the calculation as it progresses. The cache key is an expression that is evaluated for each stream item, and of course it can use the existing value of the attribute, in other words, to value it had in the previous stream item processed in the stream calculation. This allows expressions to use the "persistent" attribute value on subsequent stream items. The expression provided in the Cache Key is evaluated for each stream item so that this "persistent" attribute can refer to multiple value keyed on the "Cache Key".
Indexed Tick this option if this field should be indexed in the underlying database. An indexed field should be used to increase performance on very large streams in the following situations:-
  • When 1 or more output pipes from the stream uses the field to 'Filter' the stream.
  • When 1 or more output pipes from the stream uses the field in a 'Sort/Group' by action.
Description Description of the attribute.

Form Icons

The form provides the standard form icons as well as the following:

Shows the list of attribute functions available in CenterView.

See Also