Questions

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Revision as of 17:04, 1 February 2013 by Raugh (talk | contribs) (Added "Where are the Discipline Dictionaries?")
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Asked Questions

Doesn't matter if they're "frequently asked" at this point - if you have a question, please add it to this page. We'll try to get an answer posted ASAP.


Where Can I Find...?

PDS4 documentation
http://pds.nasa.gov/pds4/doc/index.shtml
This site lists the manuals and guides produced by PDS for PDS4 users. Here you'll find the Standards Reference, the Data Dictionary, the Information Model Specification, and a collection of tutorials and handbooks on various subjects. Be careful of version numbers while PDS4 is still in development - they are not always sequential!
PDS4 Schemas
http://pds.nasa.gov/pds4/schema/index.shtml
Here, too, be on the look-out for non-sequential version numbers.
PDS2010 Software
http://pds.nasa.gov/pds4/software/index.shtml
This includes the PDS validator software, which you should probably learn to use.
Standard Value Lists for PDS4 keywords?
There are three places:
  1. The Data Dictionary document. This is a contextual dictionary, in other words the standard value list will be dependent on what class the keyword appears in, and will be different for different classes. There's a tutorial available from the documentation page, above, on how to use the Data Dictionary.
  2. In the Schematron file. If you prefer reading code to reading the Data Dictionary, or you just find it easier to search ASCII text, open the corresponding Schematron file and look for the class containing the keyword, and then the keyword itself. You should find one rule that enumerates the entire standard value list.
  3. On the Standard Values Quick Reference page of this wiki, maintained for the convenience of SBN data preparers.
Unfortunately, none of these currently has definitions for any of the standard values.

Where's the Master Schema?

The PDS Engineering Node maintains a page for downloading the system schemas here:

http://pds.nasa.gov/pds4/schema/index.shtml

It contains the PDS master schemas, as well as the schema forms for the discipline-specific dictionaries. (These are still in development.)

The page is sorted by namespace abbreviations (for example, pds for the core namespace; sbn for the small bodies discipline dictionary; etc.). The exception is the ops (Operations) "namespace", which doesn't really exist as a separate namespace - it refers to a set of classes included in the PDS namespace that support PDS4 back-end processing and validation. For example, the classes used to load local data dictionary information into the Dictionary Data Base are considered part of the ops collection within the pds namespace. There are two flavors of Master Schema available: one containing only the pds namespace definitions containing the core label classes; and one that contains both the pds and the ops definitions. Unless you are creating a local data dictionary, the core-only "PDS" version is all you need. Scroll down to the PDS (pds) namespace heading, and you'll see that multiple versions are available. You want the version that is listed first. Ignore the version numbers - the version numbers are not sequential!

For this version, you will see three files with the same file name but different extensions. As of this writing, for example, the current version is version 03. The files available for download are:

PDS4_PDS_0300a.xsd
This is the Master Schema File. It is an XML Schema file containing all the data structure classes, meta data classes, and data types that define the core PDS requirements. You use it to create and validate labels, Validating XML editors that understand XML Schema will be able to use this file.
PDS4_PDS_0300a.sch
This is the companion Schematron file to the Master Schema. It contains a series of rules that enforce additional requirements, over and above what the Master Schema itself can enforce, on the attribute values and cross-relationships (like, you must use either this attribute or that one but not both). Try to find yourself a validating editor that also knows how to apply Schematron validation, and you'll save yourself some trouble later on. The PDS validation took references both of these files.
PDS_4_PDS_0300a.xml
This is a label for the previous two schemas. If for some reason you want to reference either the Master Schema or the Schematron file in some other product label, you'll find the logical ID for them in this label. You can also use this label if you want to include the schemas as documents in a collection you're building. You don't need this file for creating or validating product labels, so you can ignore it for your own processing.

You'll find a similarly named set of three files for all the lastest versions of the schemas on this page, serving the same functions for their respective namespaces as the above files do for the pds namespace.


Where are the Discipline Dictionaries?

Discipline dictionaries can be referenced by any label in the <Discpline_Area>, but in order to reference them in the label you need to download the schema that defines that discipline namespace and the classes and attributes within it - in other words, you need the schema form of the discipline dictionary (as opposed to a human-readable form, say).

The discipline dictionaries can be found listed on the same schema page as the Master Schema:

http://pds.nasa.gov/pds4/schema/index.shtml

The format for file naming follows the conventions mentioned above for the Master Schema, although not all discipline schemas will have a Schematron file (all will have an XML Schema file).

In some cases, your PDS consultant may direct you to use a pre-release version of a discipline schema. In this case the corresponding file(s) will be sent directly to you by the consultant or by the discipline node.