Class Name: Property Characteristic

Superclass - SEDRIS Abstract Base

Definition

Additional information about how to use, interpret or further specify a Property subclass: Property Value, Table Property Description. It consists of an enumeration that designates the the type of information, and a value for the designated attribute.

Primary Page in DRM Diagram:

• 6

Example

1. A Property Value for bridge length has two Property Characteristics to specify maximum length and length precision:

   First Property Characteristic

   • meaning = SE_MAX_VALUE
   • characteristic_value. value_type = SE_PDV_INT_16
   • characteristic_value.u. int16_value= 32767

   Second Property Characteristic

   • meaning = SE_TOLERANCE
   • characteristic_value. value_type = SE_PDV_INT_16,
     
   • characteristic_value.u. int16_value= 1

2. A sentinel value (some out of valid range value, say -10000), used for a Property Grid of Air Temperature measurements, to indicate locations where no measurement was taken. (This would have meaning= SE_DATA_MISSING.)
3. A sentinel value, used for a Property Grid of water salinity data where part of the grid covers land, marking posts for which the measurement makes no sense. (This would have meaning = SE_POINT_EXCLUDED).

FAQs

Why would a Property Value require a Property Characteristic?

If a Property Value had associated with it a valid range of values or a precision value (as is sometimes found in FACC attribute specifications), then each of these associated values could be attached to the Property Value with a Property Characteristic.

Shouldn't a value's range and precision information be part of metadata?

They can be, but metadata information is not readily computer- code accessible. If, for example, your application wants to plot table data, knowing the valid range of values will help to scale the plot. As a second example, knowing precision information will determine the appropriate round-off to use when converting data units.

How do Table_Property Description instances in the signature of a Data Table use Property Characteristics?

In addition to specifying value ranges, precision, and tolerances, a given Table Property Description of a Data Table can use a Property Characteristic to specify information that applies to all cells in the Data Table, such as a sentinel value that flags a special meaning to certain values. A Property Characteristic can also be used to indicate that a certain Data Table property is in fact constant in this particular instance of the table.

Why are Data Table sentinel values needed?

Often Data Tables are incomplete for various reasons. Typically a set of special values is selected to flag missing data. Such special values are selected to be out of the valid range of values for the parameter in question. Since the valid range of a parameter varies by data set as well by Table_Property_Description type, these special values vary accordingly. Property Characteristics provide a means to associate specific sentinel values and their meaning with a specific Table Property Description of a specific Data Table.

What are the units of a Property Characteristic characteristic_value?

The characteristic_value is measured with the same unit as the Property subclass that aggregates it.

What is the difference between SE_MAX/MIN_VALUE and SE_UPPER/LOWER_BOUND?

SE_MAX/MIN_VALUE is intended to give the nominal or legal range of values for this type of data as opposed to this instance of the data. SE_UPPER/LOWER_BOUND is intended to supply a tighter bound for the given instance of numeric data. If both sets of characteristics are supplied then:
SE_UPPER_BOUND <= SE_MAX_VALUE
SE_LOWER_BOUND >= SE_MIN_VALUE

Is SE_UPPER_BOUND the same as the least upper bound for the data and similarly is SE_LOWER_BOUND the greatest lower bound?

Not necessarily. But the tighter the bound the more useful is the information provided. If possible they should be the least upper greatest lower bounds.

How are the SE_UPPER_BOUND, SE_LOWER_BOUND values used?

They can be used by the data consumer for scaling graphs, checking data validity, etc. When supplied for a Data Table signature item, together with SE_TOLERANCE or SE_SIG_DIGITS values, a SEDRIS Write API implementation may be able to use this information to compress the Data Table.

Constraints

Component of (one-way)

• one or more Properties

Field Elements