3.2 Basic quantities and types

Spectrum data model is desingned to be easy-to-use and self-decribing. It consists of several classes that have member varibles of simple types representing physical quantities. These quantities have different data type described below. They also have a Unit, Ucd and Key field to describe metadata.

class Param

All quantity classes are inherited from the Param class.

object Value
Numeric or textual value of the quantity is stored in this member variable. May have different data type according to the different types detailed below.

string Unit
Represents the unit of the numerical quantity in a standard format. Currenty the only valid units are A (Angtsroms) for wavelength, 10-27 ... for flux-density. Note that the services don't preform unit checking and conversion!

Ucd
UCD is unified content description which is an IVOA standard for describing astronomical data. It is designed to help identifying the contents of variables in heuristic unit conversion programs.

Key
Used for VOTable conversion, since the VOTable standard defines this attribute. <detailed description>

class IntParam : Param

Its Value field represents a 64 bit long signed integer number.

class DoubleParam : Param

Its Value field represents a 64 bit long double precision signed floating point number.

class BoolParam : Param

Its Value field represents a boolean value which can be either true or false.

class TextParam : Param

Its Value field represents a variable length unicode string. Maximum size usually determined by the underlaying database, which may limit the number of storable characters thus values may be truncated.

class TimeParam : Param

Its Value field represents an 8 byte long date/time value. It stores year, month, day, hour, minute, secound and tick info. Since time values are transfered in a string format (XML) over the network, there's no compatibility issue with the time model of the different programming languages, since back conversion is always done by the web service library in the right way. In the spectrum data model astronomical time system is usually coded into the UCD or stored in an other variable.

class PositionParam : Param

Its Value field represents an (ra, dec) pair in degrees, in decimal format in a string separated by comma.

class TimeInterval

TimeParam Min
Represents the minimum of the time interval in a TimeParam object.

TimeParam Max
Represents the maximum of the time interval in a TimeParam object.

class DoubleInterval

DoubleParam Min
Represents the minimum of the interval in a DoubleParam object.

DoubleParam Max
Represents the maximum of the interval in a DoubleParam object.

class Group

This class is used to group parameters only, required for easy VOTable conversion. Several derived classes are defined discussed in details later.