Filling Out Context Object Classes

Following are the context object classes and their attributes. Only one instance of one of these may appear in any context product. Only the context objects that a data preparer is likely to use are listed. There are some additional objects used for PDS system maintenance. Your PDS consultant will advise you directly in the unlikely event you need to create context products for these.

NOTE: I believe it is true that in all cases it is the <title> attribute found in the <Identification_Area> that contains the official name of whatever it is the context object is describing, although this does not appear to be stated in the PDS4 documentation. While <title> is always required, <name> is frequently optional. If you do supply a value for <name>, the value should be very close to, if not the same as, the title in the Identification_Area.

For additional explanation, see the PDS4 Standard Reference, or contact your PDS node consultant.

Note that in the PDS4 master schema, all classes have capitalized names; attributes never do.

<Agency>

This is used to provide basic information about an agency, like NASA or ESA.

<name>

REQUIRED

This must be identical to either the value of the <title> or one of the <alternate_title>" attributes listed in the Identification_Area.

<description>

REQUIRED

This is for a brief description of the agency named.

<Facility>

This class is used for facilities like a terrestrial labs and observatories. Although every field within it is optional (because different facilities have different known attributes), you should never send an empty <Facility> class to SBN for archiving.

<name>

OPTIONAL

This should be the same as or equivalent to the value of the <title> attribute in the Identification_Area.

<type>

OPTIONAL

This must be one of the two standard values Laboratory or Observatory. If you need a different value, contact your PDS consultant.

Note: This attribute will be required for SBN-generated or reviewed Facility objects.

<address>

OPTIONAL

This is a text field to hold the address (mailing address, street address or both) of the facility.

<country>

OPTIONAL

This attribute is for the name of the country. It's not clear why this is here. If you use it, I suggest you use it for the full name of the country, with the intention of using it for searching out ground-based observatories and related data by country of origin.

<description>

OPTIONAL

This is a place for free-format text to provide additional relevant details about the facility.

<Instrument>

Use this for anything that can be reasonably considered to be an instrument, in the "taking data" sense.

<name>

OPTIONAL

This should be the same as or equivalent to the value of the <title> attribute in the Identification_Area.

<type>

REQUIRED

This must be one of the standard values listed in the Standard Values Quick Reference. If the instrument you're describing corresponds to more than one of these values, you may repeat the <type> attribute.

<model_id*gt;

OPTIONAL

If the instrument has a model number or the equivalent, it can be recorded here.

<naif_instrument_id>

OPTIONAL

If the instrument being described has a NAIF identification code, type it in here.

<serial_number>

OPTIONAL

If the instrument has a known serial number, this is the place for it.

<description>

REQUIRED

Free-format text description of the instrument.

<Instrument_Host>

This class is for describing the hardware an Instrument is physically mounted on/to.

<name>

OPTIONAL

This should be the same as or equivalent to the value of the <title> attribute in the Identification_Area.

<version_id>

OPTIONAL

Note: The version of the Instrument_Host product is in the Identification_Area. This version_id should never be used in SBN Instrument_Host context products.

<type>

REQUIRED

This must be one of the standard values Earth Based, Rover or Spacecraft.

Note: These values don't make sense in many cases, or when compared to each other. So for SBN data, use these rules (use them very roughly, if necessary): If it moves through space, it's a Spacecraft If it moves through or on anything else, it's a Rover If it doesn't move, it's Earth Based

<naif_host_id>

OPTIONAL

If the host has a NAIF identification code, this is the place to put it.

<serial_number>

OPTIONAL

If the host has a known serial number, it can be recorded here for posterity,

<description>

REQUIRED

This is a free-format text description of the instrument host.

<Investigation>

This class is for describing a mission, a coordinated observing campaign, or some other large-scale, organized effort to collect data.

<name>

OPTIONAL

This should be the same as or equivalent to the value of the <title> attribute in the Identification_Area.

<type>

REQUIRED

This must be one of the four standard values: Individual Investigation, Mission, Observing Campaign, Other Investigation.

<start_date>

REQUIRED

The date of the start of the investigation, in ISO 8601 format.

Note: For some reason this is required for all investigations, and can never be nil. If you are trying to write a context product for something without a clear starting point, seek advice from your PDS data consultant.

<stop_date>

REQUIRED

The date of the end of the investigation, in ISO 8601 format.

If this is not available for some reason (most often that the investigation isn't over yet), you can use the nilreason attribute, like this:

    <stop_date xsi:nil="true" nil_reason="anticipated"/>

<description>

REQUIRED

This is a free-format text description of the investigation.

<Other>

Use this context class only if no other class is reasonably applicable.

<description>

REQUIRED

This free-form text should provide whatever key details about the context object are relevant to the archive. Best to be explicit about this if you're using the Other context object.

<Target>

Use this class when it is useful to define a target context object for an observational target. It provides a permanent hub for linking to additional description and information (via the Reference_List, primarily).

Target products should be created when such a hub is wanted/needed. For example, if the target is a piece of hardware, like a calibration lamp, with specific characteristics that can be/are described by associated document products in the archive (or published references outside the archive), a Target product can link the target name to those references via the <Reference_List> and could be very helpful to end users. Target products for half a million anonymous asteroids - not so much.

NOTE: SBN data preparers should never create Target context products for natural targets (comets, asteroids, planets, etc.). If you should ever require one for some reason, SBN will create it for you.

<name>

OPTIONAL

This should be the same as or equivalent to the value of the <title> attribute in the Identification_Area.

<type>

OPTIONAL

If present, the value must be one of the standard values from the list in the Standard Values Quick Reference. If more than one of these types applies to the Target, you may repeat the <type> attribute.

<description>

REQUIRED This free-format text field must contain a description of the target itself.

<Telescope>

This class is designed for identifying and providing key details about terrestrial telescopes, fixed and roving.

<name>

OPTIONAL

This should be the same as or equivalent to the value of the <title> attribute in the Identification_Area.

<aperture>

REQUIRED

This attribute holds the diameter of the telescope aperture. You must specify a unit of length for this value. For example:

    <aperture unit="m">1.3</aperture>

<telescope_longitude>

OPTIONAL

The longitude of a permanent telescope mounting. The value is a single floating-point number, and you will need to specify units for the value. For example:

  <telescope_longitude unit="deg">123.4567</telescope_longitude>

Note: This attribute is poorly defined in the PDS4 data dictionary, as the direction of measurement is not indicated and the unit is allowed to be any angular unit. The range is 0-360 degrees. Until these issues are corrected, always indicate the direction of measurement in the <description> attribute, and always state longitude in degrees.

<telescope_latitude>

REQUIRED

North latitude of a permanent telescope mounting. The value is a single floating-point value, and you will need to specify units for the value. For example:

  <telescope_latitude unit="deg">-12.34567</telescope_latitude>

Note: The definition of this attributes in the PDS4 data dictionary is a little fuzzy. It should be North latitude (South being indicated by negative numbers), and it must be stated in degrees.

<altitude>

REQUIRED

This is the altitude of the telescope above sea level. You will have to specify units for this value:

    <altitude unit="m">14000</altitude>

<coordinate_source>

REQUIRED

This must be one of the values in the Standard Value Quick Reference. If you have a value that doesn't fit, let me know. Use Unknown for mobile telescopes.

<description>

OPTIONAL

This is for a free-format text description of the telescope.