The SEDRIS Data Representation Model
APPENDIX A - Classes
Axis

Abstract Class Name: Axis

Superclass - <SEDRIS Abstract Base>

Subclasses

Definition

An instance of this DRM class (that is, of one of its concrete subclasses) specifies a set of values of an independent variable to be used to organize the dependent values in a <Data Table>.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

Example

  1. A table of Digital Terrain Elevation Data (DTED) contains terrain elevation data sampled in a grid of regularly spaced longitude and latitude points. The <Axes> of such a table would be longitude and latitude.

  2. A table of ocean temperature and salinity data taken at varying depths by an expendable bathythermograph can be captured in a table. Such a table would have depth as an axis, and temperature and pressure would be <Table Property Descriptions>. If these data were taken at intervals along a path, the locations on that path (say longitudes) would form a second <Axis> of the now two-dimensional table.

FAQs

How are the values on an <Axis> related?

The values on a single <Axis> shall be distinct values of a single variable specified by the axis_type. If the axis is numeric, the values shall be arranged monotonically.

Can an <Axis> have no values or a single value?

An <Axis> shall have at least one value; an axis with no values is a violation of SEDRIS' constraints. If the <Axis> has a single value, this implies that all of the data in the table shares that value. There may be better ways to associate a single value with all the table entries.

Given 2 variables, where certain combinations of values for these 2 variables are impossible or meaningless, can a data provider combine these 2 variables on a single <Axis> in order to exclude the meaningless cells?

No. A data provider should include the meaningless cells, and set a value for EMC_NOT_APPLICABLE, and use it for those cells.

Constraints

Component of (two-way)

Inherited Field Elements

This class has no inherited field elements.

Field Elements

SE_Element_Type axis_type; (notes)
EDCS_Unit_Code value_unit; (notes)
EDCS_Scale_Code value_scale; (notes)
SE_Short_Integer_Positive axis_value_count; (notes)

Notes

Fields Notes


axis_type

 This specifies the property being described by the given <Axis>.

value_unit

 This specifies the unit of measurement of the <Axis>, which shall
 be compatible with the requirements imposed by axis_type.

 If axis_type does not require a unit of measurement, for example,
 if axis_type requires a value_type of STRING, then value_unit
 shall be set to EUC_UNITLESS.

value_scale

 This specifies the scale applicable to value_unit.

 If axis_type does not require a unit of measurement, for example,
 if axis_type requires a value_type of STRING, then value_scale
 shall be set to ESC_UNI.

axis_value_count

 This is the number of "hash marks" along the <Axis>.
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Last updated: October 1, 2002 Copyright © 2002 SEDRIS™